Menschen für Menschen Foundation

Agro-Technical and Technology College

Agro-Ecology Department

Postharvest Physiology and Handling of Horticultural Crops

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 CHAPTER I

Introduction

1.1 History of Postharvest Technology

Post harvest technology is inter-disciplinary "Science and Technique" applied to agricultural

produce after harvest for its protection, conservation, processing, packaging, distribution,
marketing, and utilization to meet the food and nutritional requirements of the people in relation
to their needs. The process of developing of post harvest technology and its purposeful use needs
an inter-disciplinary and multi-dimensional approach, which must include, scientific creativity,
technological innovations, commercial entrepreneurship and institutions capable of inter-
disciplinary research and development all of which must respond in an integrated manner to the
developmental needs.

The word post means after and harvest refers to the process of harvesting; gathering the matured
produce or the produce obtained from a farm, “Post-harvest” therefore refers to events after
harvest, when the harvested produce had been cut off from the source of nutrition from the
parent plant.

A clear understanding of biochemical and physiological changes in fruits and vegetables during
post harvest operations will enable persons involved in handling, transportation and storage
operation to regulate certain critical parameters.

 Preservation, Conservation, Quality control/enhancement, processing,

Packaging, storage, distribution, marketing and

 Utilization to meet the food and nutritional requirements of consumers in

relation to their needs.

Postharvest technology is also a human device to serve human needs, and includes everything
that happens to crops between harvest and human utilisation.

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Post-harvest technology is the application of scientific and engineering principles to the
handling, storage, packaging, distribution, and sale of agricultural produce after it has been
harvested. Post-harvest technology is used to improve the quality and extend the shelf life of
food.

Importance of postharvest technology

Post-harvest technology lies in the fact that it has capability to meet food requirement of growing
population by eliminating avoidable losses making more nutritive food items from low grade raw
commodity by proper processing and fortification, diverting portion of food material being fed to
cattle by way of processing and fortifying low grade food and organic wastes and by-products
into nutritive animal feed. Post-harvest technology has potential to create rural industries. It is
possible to evolve appropriate technologies, which can establish agricultural based rural
industries.

Contribution to food security

 Post-harvest development contributes to food security in several ways.

 Improved storage technologies such as biological pest control or

controlled atmosphere storage reduce post-harvest losses, thereby
increasing the amount of food available for consumption

Contribution to living standards

 Developing post-harvest systems has the potential to raise living

standards in urban and rural areas. In urban areas, it makes food
available more efficiently and at a lower cost.

 In rural areas, post-harvest activities can benefit the poorest members of

society in particular, through its contribution to farm and non-farm
income.

Gender issues

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  Female participation in agro industry is growing rapidly and particularly
in poorer countries

 The availability of processed food may reduce demands on female labor

in preparing food, thus releasing this labor for other purposes.

Environmental sustainability

 An effective post-harvest system minimizes unnecessary production,

thus saving on scarce land and water resources, and

1.2. Importance of post-harvest physiology

The word Physiology is a branch of biology (study of all life or living matter), physiology deals
with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the
physical and chemical phenomena involved.
Successful postharvest handling of fruit and vegetables requires knowledge of the postharvest
physiology of the fruit and how the fruit physiology determines the best handling practices to
maintain and develop high fruit quality.

Postharvest physiology is about the plant response to technologies and other applications that
extend shelf life and quality and delay senescence (plant death).

The postharvest physiology of fresh fruit and vegetables has in recent times become an important
subdivision of both plant physiology and horticulture.

1.3. Extent of post-harvest losses of horticultural crops

All fresh horticultural crops are high in water content and are subject to desiccation, mechanical
and physiological injury. They are also susceptibility to attack by bacteria and fungi, with
pathological breakdown. Biological (internal and external) causes of deterioration include
respiration, ethylene production and action, rates of compositional changes, mechanical
physiological injuries, water stress, sprouting and rooting, physiological disorders, and
pathological breakdown. The rate of biological deterioration depends on several environmental
(external) factors, including temperature, humidity, air, frost and atmospheric gases composite,
and sanitation procedures.

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Postharvest loss has been defined as a measurable quantitative and qualitative loss of a given
product at any moment along the postharvest chain and includes the change in the availability,
edibility, wholesomeness or quality of the food that prevents it from being consumed.

Qualitative Losses is type of loss such as loss in edibility, nutritional quality, caloric value, and
consumer acceptability of the products are much more difficult to assess than quantitative losses.
Standards of quality and consumer preferences and purchasing power vary greatly among
countries and cultures. For example, elimination of defects from a given commodity before
marketing is much less rigorous in developing countries than in developed countries.

Quality of harvested produce is assessed visually by observing the shape, the size, the colour and
general cleanness of the produce including absence of insects. Other parameters of quality
include moisture content, taste, odour and firmness.

Quantitative Losses This is a measurable reduction in harvested produce. This reduction might
be in terms of weight or volume. This type of losses can occur through different means; for
example moisture which is a substantial part of harvested produce can be lost between harvest
and consumption. This will lead to reduction in weight or volume. Shrinkage in oranges,
tomatoes and potatoes due to moisture loss in transit or storage this will also reduce the weight.
The effect of moisture loss go beyond reduction in quantity as it sometimes leads to quality
reduction.

About one-third of the food produced is wasted in developed and developing countries which
accounts to 1.3 billion tons per year. In medium- and high-income countries, a lot of food is
discarded while it is still suitable for human consumption (more than 40% of the losses occur at
the retail and consumer levels) while in developing countries, food losses occur early in the food
supply chain at postharvest and processing stages. About 30-40% of fruits and vegetables are lost
or discarded after leaving the farm gate. Fresh fruits and vegetables are wasted throughout the
food supply chains, from initial agricultural production down to final household consumption.

The Sub Saharan Africa (SSA) net food production per annum is within 230 million tons.
Greater portions of this amount is lost due to various factors ranging, for example, poor
infrastructure, low levels of technology and low investment in the food production systems, pest,
inadequate policies, storage, climate and other factors.

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 1.4. Pre- and post- harvest factors influencing post-harvest quality

The issues that influence produce quality include obvious things, such as harvest maturity and
cultivar or variety, but also the climate and soil in which it was grown, chemicals which have
been applied to the crop and its water status. Many of these factors can also interact with time
such as when fertilizers or irrigation is applied or the weather conditions near to the time of
harvest.

The soil type and its fertility affect the chemical composition of a crop. Excess or deficiency of
certain elements from the crop can affect its quality and its postharvest life. For example many
storage disorders of apples are associated with an imbalance of chemicals within the fruit at
harvest.

Maintaining good, long-term soil health and quality remains a primary goal of organic
production systems. Achieving this goal will ultimately benefit the postharvest quality of fruit
and vegetables grown on the farm, as the availability of the optimal levels of plant nutrients
throughout the growing season will allow for optimal quality of the vegetables throughout the
packing and distribution processes. Deficiencies or overabundances of certain plant nutrients can
affect positively or negatively a crop’s susceptibility to physiological disorders, disease, and
negative composition and textural changes. When optimizing soil fertility to improve postharvest
quality, it is important to remember that these may not be the same soil nutrient levels that
produce the highest yields.

The texture of the soil on which certain vegetable crops are grown may also affect the
postharvest quality. For example, carrots grown on muck soils have been shown to have a greater
concentration of terpenoids, a chemical that imparts a bitter flavor, than carrots grown on sandy
soil.

A) Related to plants
Crops: Quality of the fruit and vegetables are varies from crop to crop. e.g. jackfruit, potato, oni
on, pumpkin, garlic etc. having good quality in relation to shelf life while apple, mango, cherry, s
trawberry, tomato, capsicum, okra, brussels sprout, chinese cabbage, carrot, radish attract more t
o consumers due to their attractive appearance.

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Cultivars: The quality of seed or plant material is an important factor that controls the quality of
the fruit and vegetable produced. Several parameters of quality are controlled genetically.

Irrigation: Irregular watering usually reduces fruit size, increases splitting, physiological disorde
rs, reduces water content in the plant or plant part etc. Adequate soil moisture during the pre
harvest period is essential for the maintenance of postharvest quality. Water stress during the
growing season can affect the size of the harvested plant organ, and lead to soft or dehydrated
fruit that is more prone to damage and decay during storage. On the other hand, vegetables
experiencing an excess of water during the growing season can show a dilution of soluble solids
and acids, affecting flavor and nutritional quality.

Excess moisture on the harvested vegetable can also increase the incidence of postharvest
diseases. To minimize the amount of water on the harvested vegetable brought into storage, it
may be beneficial to choose surface or subsurface irrigation rather than overhead irrigation.
Vegetables harvested in the early morning, during rainy periods, and from poorly ventilated
areas can also experience increased postharvest decay.

Fertilization: Poor management of fertilizers will increase physiological disorders due to deficie
ncies of some minerals or increase of other leading to toxicity. In both cases, quality will be nega
tively affected. The application of Ca and high fruit Ca concentration resulted in increased firmn
ess, reduced disease incidence, chilling injury, physiological disorders and ripening and improve
storaility. Application of excess N element is detrimental in terms of quality attributes.

Crops that contain high levels of nitrogen typically have poorer keeping qualities than those with
lower levels. Application of nitrogen fertilizer to pome fruits and stone fruits shown to increase
their susceptibility to physiological disorders and decrease fruit colour.

Nitrogen is an important mineral element that is used by almost all crops. Nitrogen, as a key
component of plant proteins, plays an important role in plant growth and development (Ritenour).
Because of nitrogen’s involvement in protein synthesis, soil nitrogen deficiencies may lead to
lower protein concentrations in vegetables, thereby affecting the nutritional composition of the

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crop. Adequate soil nitrogen supplies allow for the optimal development of vegetable color,
flavor, texture, and nutritional quality.

Excess soil nitrogen can be problematic as well. Research has shown that too much soil nitrogen
can reduce the vitamin C content of Green leafy vegetables such as swiss chard. Excess nitrogen
may lower fruit sugar content and acidity. In certain situations, leafy green plants may
accumulate excess soil nitrogen, leading to high concentrations of nitrates in the harvested greens.

Specific examples of excess nitrogen negatively affecting crop quality include (Ritenour):

 Altered celery flavor

 “Brown-checking” of celery

 Weight loss of sweet potato during storage

 Hollow stem in broccoli

 Soft rot in stored tomatoes

The high rates of application of nitrogen fertilizer to apple trees could adversely affect the
flavour of the fruit. High nitrogen increased the susceptibility of apple fruit to flesh and core
browning during storage.

Phosphorus and potassium also play very important roles in plant growth and development.
Phosphorus is a key component of DNA and plant cell membranes. This element also plays a key
role in plant metabolic processes. Potassium is important in plant water balance and enzyme
activation. High levels of soil phosphorus have been shown to increase sugar concentrations of
fruits and vegetables while decreasing acidity. High levels of soil potassium often have a positive
effect on the quality of vegetables. Increased soil potassium concentrations have been shown to
increase the vitamin C and titratable acidity concentrations of vegetables and improve vegetable
color. Potassium also decreases blotchy ripening of tomato.

High Phosphorus concentration minimize the weight loss, sprouting and rotting in onions
compared with lesser applications during storage. Phosphorus nutrition can alter the postharvest

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physiology of cucumber fruits by affecting membrane lipid, membrane integrity and respiratory
metabolism.

The application of potassium fertilizer to watermelons decrease the respiration rate of the fruit
after harvest. In tomato fruits, dry matter and soluble solids content increased as the potassium
rate increased. The application of potassium to citrus trees could affect the shape of their fruits
and increase their acidity, although this effect was not observed when potassium was applied to
banana plants.

Calcium is an important to plant cell walls and membranes. Deficiencies of soil calcium have
been associated with a number of postharvest disorders, including

 Blossom end rot of tomato, pepper, and watermelon; brown heart of escarole; blackheart
in celery; and tip burn of lettuce, cauliflower and cabbage.

 Also, low calcium levels in fruit increased the susceptibility of apples to flesh and core
browning.

 The physiological disorder of stored apples called ‘bitter pit’ is principally associated
with calcium deficiency during the period of fruit growth and may be detectable at
harvest or sometimes only after protracted periods of storage. The incidence and severity
of bitter pit is influenced also by the dynamic balance of minerals in different parts of the
fruit as well as the storage temperature and levels of oxygen and carbon dioxide in the
store atmosphere.

Some beneficial effect of calcium

 High soil calcium concentrations reduce these disorders and are associated with other
postharvest benefits, including increased vitamin C content,
 extended storage life, delayed ripening, increased firmness, and reduced respiration and
ethylene production
 High calcium fertilizer levels reduced the acidity of strawberries and played a part in loss
of visual fruit quality after harvest.

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Insect and pest: Pathogens and insects have a very negative effect on quality.
Poor management of plant protection programmes can lead to very poor quality and reduced yiel
d. Insect pest problems during the growing season can also affect postharvest quality, both
obvious and no-so obvious ways. Visible blemishes on the vegetable surface caused by insect
feeding can have a negative effect on the appearance of vegetables, thus decreasing their appeal
to consumers. Feeding injury on vegetables by insects can lead to surface injury and punctures,
creating entry points for decay organisms and increasing the probability of postharvest diseases.
In addition, the presence of insect pests on vegetables entering storage leads to the possibility of
these insects proliferating in storage and becoming an issue.

B) Related to Environments
Temperature: Temperature is the most important environmental factor that affects quality,
very low or very high temperature may injure sensitive crops. Temperature has been found to inf
luence fruit shape, size, colour and other quality parameters. Pineapple fruits grown in winter mo
nths or in cool growing areas had reduced eating qualities due to lower sugar/acid ratio. Adequat
e high intensity and quality is important for the formation of some colour. Wind and rain may ca
use negative effects on some crops.

Radiation: Radiation interception by fruit has amarked effect on the quality attributes of
fruits. Any factor that reduces radiation interception results in reduced soluble solids, higher acid
ity and abnormal skin color development. Low light intensity can reduce the firmness of fruits at
harvest and during storage. Low light intensity increases postharvest disease incidence. UV light
has been shown to influence accumulation of total polyphenol contents in tomatoes. Coffeic acid,
ferulic acid and p-coumaric acid contents were found to be about 20% higher in tomatoes grown
with UV light (290 to 400 nm) as compared with samples grown under UV restriction.

Relative humidity: Relative humidity plays an important role in determining fruit quality. Highe
r relative humidity reduces water and Calcium movement into the
fruit. In contrast, higher relative humidity around the plant increases calcium accumulation into t
he fruit by reducing leaf evapotranspiration.

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 CHAPTER II

Structure and postharvest quality of fruits and vegetables

2.1. Edible fruit and vegetable parts

Fruits are seed-bearing parts of large plants which are formed from the ovary after flowering
which may be dry or fleshy. The term is commonly restricted to fleshy fruits, which are of
economic and nutritional importance to humans. Vegetables, on the other hand are plants
cultivated for an edible part, e.g. root, tuber, leaf or flower buds.

Fruit and vegetables are both major food products and key ingredients in many processed foods.
Consumers increasingly require food products that preserve their nutritional value, retain a
natural and fresh color, flavor and texture, and contain fewer additives such as preservatives and
anti-oxidants. There is consistent evidence, primarily from epidemiology, that diets high in
vegetables and fruits can decrease the burden of chronic disease, with the evidence for reduced
risk of many cancers being particularly strong.

Current scientific evidence also suggests a protective role of fruits and vegetables against
cardiovascular disease and evidence is accumulating for a protective role in stroke. Fruit and
vegetable consumption has been linked to reduced cardiovascular disease and stroke. In addition,
a new scientific base is emerging to support a protective role of fruits and vegetables against age-
related macular degeneration, chronic obstructive pulmonary disease, diverticulosis and other
digestive disorders, and possibly hypertension.

Vegetables can be from any part of the plant. Their origin as a root, shoot, leaf, flower bud, fruit
or other part affects how easily they can be handled and stored.

Unlike fruit, which are derived from flowers, vegetables cannot easily be defined. Vegetables are
derived from many different parts of plants. Some are actually fruit; others are buds, leaves,
stems, roots or storage organs. Where the vegetable comes from on the plant affects how well it
stores and many of its sensory qualities.

Vegetables can generally be grouped into three categories:

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 1. Bulbs, roots and tubers
2. Flowers, buds, stems and leaves
3. Fruit, seeds and pods

Root crops include carrot, radish, beet, turnip, and sweet potato. Stem vegetables are asparagus
and potato. The yield and quality of root and stem vegetables are affected by soil texture,
fertility, and irrigation. Leafy crops include lettuce, cabbage, celery, spinach, kale, and mustard,
which are very perishable. The edible parts of cauliflower, broccoli, and artichoke are immature
flower buds. Immature fruits are harvested from pea, snap bean, lima bean, summer squash,
cucumber, okra, sweet corn, and eggplant. But actually we eat the immature seeds of lima beans
and sweet corn. Edible parts of cucurbits (pumpkin, white gourd, squash, muskmelon, and
watermelon), tomato, and pepper are mature fruits.

Vegetables: Vegetables generally show no sudden increase in metabolic activity that parallels
the onset of the climacteric in fruit, unless sprouting or growth is initiated. Vegetables can be
divided in to three main groups: (a) Seeds and pods; (b) Bulbs, roots and tubers and (c) Flowers,
buds, stems and leaves

a) Seeds and pods, if harvested fully mature, as is the practice with cereals; have low metabolic
rates due to low water content. In contrast, all seeds consumed as fresh vegetables e.g.
legumes and sweet corn (baby corn), have high levels of metabolic activity, because they are
harvested at an immature stage, often with the inclusion of non-seed material e.g. bean pod
(pericarp). Generally the seeds are sweeter and tenderer at an immature stage. With
advancing maturity, the sugars are converted to starch with the resultant loss of sweetness,
the water content decreases and the amount of fibrous material increases. Seed for
consumption as fresh produce are harvested when the water content is about 70%; in contrast,
dormant seeds are harvested at less than 15% water content.
b) Bulbs, roots and tubers are storage organs that contain food reserves needed when plant
resumes growth. When harvested, their metabolic rate is low and under appropriate storage
conditions, their dormancy can be prolonged.
c) Edible flowers, buds, stems and leaves; vary greatly in metabolic activity and hence in rate
of deterioration. Stems and leaves often senesce rapidly and so lose their attractiveness and

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 nutritive value. The natural flavor is often of less importance than texture, as many of these
vegetables are cooked and salt or spices are added. Besides some fruits are also consumed as
vegetables. They are either ripe (tomato, egg plant) or immature (cucumber, okra, zucchini).

2.2. Cellular components and their functions

Cell walls are important structural components of plants, affecting both the bioaccessibility and
subsequent digestibility of the nutrients that plant-based foods contain. These supramolecular
structures are composed of complex heterogeneous networks primarily consisting of cellulose,
and hemicellulosic and pectic polysaccharides. The composition and organization of these
different polysaccharides vary depending on the type of plant tissue, imparting them with
specific physicochemical properties. These properties dictate how the cell walls behave in the
human gastrointestinal tract, and how amenable they are to digestion, thereby modulating
nutrient release from the plant tissue.

Plant cells

The water pressure inside plant cells is what keeps vegetables firm and crisp. Damage to cell
membranes allows compounds kept separately inside the cell to combine and the cell contents to
leak out. This results in brown, soft and/or water-soaked areas.

Like other living things, vegetables are made up of cells. There are many different types of cells
within even a simple vegetable, and each has different functions within the plant.

Plant cells have a fairly rigid cell wall, composed mainly of cellulose, lignins and some proteins.
Calcium is critical in the formation of cell walls. If calcium is deficient (due to low soil levels or
growth faster than the rate of transport within the plant) the growing tips of fruiting vegetables
such as zucchini and eggplants will lack structural integrity and can break down. This is the
cause of blossom end rot.

The cell wall is permeable to water and solutes. Inside the cell wall is the plasmalemma, which
acts like a liner. The plasmalemma helps maintain pressure inside the cell, keeping it turgid. It is
this turgidity that keeps vegetables firm and crisp.

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Adjacent cells are glued together by a layer of pectins. A series of channels (plasmodesmata)
allows exchange of various substances between cells.

The cell contains a liquid ‘soup’ called cytoplasm. Within the cytoplasm float various structures
and organelles, each of which has a specific purpose.

These include:

 The nucleus, which contains the cell’s DNA and acts as the control centre.
 One or more vacuoles. These are reservoirs of liquid containing sugars, acids and other
materials. Some plant products (such as phenols) are stored inside the vacuoles to keep
them apart from enzymes with which they would otherwise react.
 Mitochondria, which are the cell’s power plant, converting breakdown products from
sugars into energy the cell can use.
 Chloroplasts are found in green parts of the plants. They contain chlorophyll and are
responsible for photosynthesis.
 Chromoplasts develop from chloroplasts once chlorophyll breaks down. They contain the
red and yellow pigments (carotenoids) that give some vegetables their colour.
 Amyloplasts that contain grains of starch.

There are many types of plant cells and they perform different functions for the plant. How the
plant cells are arranged and whether the vegetable has a thick epidermis and/or waxy cuticle
strongly affects ‘keeping’ quality and water loss.

Plant tissues contain many different types of cell, as well as air spaces. These include:

 Veins, consisting of:

o Xylem vessels – which transport water and minerals from the roots to the leaves.
o Phloem vessels – which transport sugars from leaves to the roots.
 Stomata and lenticels – openings that allow gas exchange between the inside and
outside of the plant tissues.
o Stomata are actively controlled by ‘guard’ cells; these open to allow gas exchange
or close to reduce water loss. They usually close at harvest in response to a small

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 drop in water pressure inside the cells. Leaves can have large numbers of stomata
spread across their surface.
o Lenticels are sunken openings that cannot be closed. They are typical of storage
organs such as sweet potato as well as cucumbers and other fruit vegetables.
o Lenticels are regions in the eperiderm where a more active phellogen produces a
tissue with intercellular spaces.
o They are generally, present on stems, roots and fruits, and practically absent on
leafy vegetables.
o Unlike stomata, lenticels are continually open for gas exchange b/n the
subepidermal cells and the atmosphere. Respiration is faster with continuous O2
supply.
o Old, overripe fruits with more lenticels tend to wilt and shrivel more than younger
fruits with fewer lenticels.
o
 Epidermal cells – the plant’s skin. These can develop a waxy cuticle, protecting the
underlying tissue against water loss. In some storage organs, such as potatoes, several
layers of epidermal cells form a corky layer protecting the underlying cells.
 Parenchyma cells – non-specialised cells that carry out functions such as photosynthesis
and form most of the internal tissue (mesophyll).
 Collenchyma cells – stretchable cells rich in pectin and cellulose that help give the plant
strength, e.g. celery strings are mainly collenchyma.

2.3. Composition and Nutritional Values of Fruits and Vegetables

Water

Most fruits and vegetables contain more than 80% of water. Cucumber, lettuces, melons 95% of
water. Actual water content and availability of water to the tissue at the time of harvest and
water content of produce vary during the day if there are diurnal fluctuations in temperature. It
is desirable to harvest when the maximum possible water content is present as it results in crisp
texture. Hence time of harvest is an important consideration especially with leafy vegetables,
which show large and rapid variations in water content in response to change in their
environment.

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Water present in two forms

(a) free water and

 Water that can be extracted easily by squeezing/pressing/cutting or pressing is called as

free.

(b) bound water and

 Water that is held so tightly by another molecule (such as a protein)

 This water is not free to act as solvent for salts and sugars.

 It can be frozen only at very low temperatures.

 The water molecules are bound to polar groups or ions on molecules such as starches,
pectin, and proteins.

Carbohydrates

Carbohydrates are generally the most abundant constituents after water and can be present as low
molecular weight sugars or high molecular weight polymers. They account for 2-40% of tissue
weight with low levels in cucumber and high level in vegetables that accumulate starch e.g.
Cassava. Sugars are mainly present in ripe fruits and starch in both vegetables and unripe fruits.
Sucrose, glucose and fructose are found mainly in fruits. Vegetables with high starch content are
important contributor to the daily energy requirement of people in many countries as human
beings can utilize starch or sugars as energy sources.

Carbohydrate functions include, among others, the storage of energy reserves and the make-up of
much of the structural framework of cells. Glucose and fructose are the predominant forms of
simple sugars found, especially, in fruits. Sucrose, the primary transport form of carbohydrate in
most plants, is a disaccharide yielding glucose and fructose upon hydrolysis. Glucose, fructose
and sucrose are water-soluble and together they comprise most of the sugars associated with the
sweet taste of fruits and vegetables. The relative proportions of glucose and fructose vary from
fruit to fruit and, to a lower extent, in the same fruit according to maturity. In many fruits (e.g.,
apple, pear, strawberry, grape) glucose and fructose are present in greater amounts than sucrose,
but in certain vegetables, such as parsnip, beetroot, carrot, onion, sweet corn, pea and sweet
potato, and in some ripe fruits such as banana, pineapple, peach and melon, the sucrose content is
higher.

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Starch from plantain, cassava, yam, sweet potato and potato gives higher energy to subsistence
groups in some developing countries. But over dependence on starchy vegetables is undesirable,
as they cannot supply enough of other essential nutrients. A substantial portion of carbohydrates
is present as dietary fibers, which is not digested and passes through the intestinal system.
Cellulose, pectic substances, hemicelluloses and lignin (polymer of aromatic compounds) are the
carbohydrate polymers that constitute dietary fibers. Fibers help preventing various diseases e.g.
appendicitis, constipation, cancer of colon, diabetes, gallstones, obesity, tumors of rectum etc.
Organic Acids

Most fruits and vegetables contain organic acids in excess of what is required for the operation of
TCA cycle and other metabolic pathways. The excess is generally stored in vacuole away from
the cellular components. Apart from their biochemical importance, organic acids contribute
greatly to taste, particularly of fruits, with a balance of sugar and acids giving rise to the
desirable taste of specific fruit. The dominant acids in produce are usually citric acid (citrus
fruits, pineapple, guava, tomato, beetroot, leafy vegetable, legumes, potato etc.) and malic acid
(banana, melon, apple, onion, carrot, lettuce etc.)

Plant lipids (Fat): -Most of the time postharvest products are relatively low in total lipids,
except for avocados 35-70%, olives30-70%, grape 0.2%, banana 0.1%; and apple: 0.06%.
Lipids comprise less than 1% of most fruits and vegetables. The avocados and olive are
exceptions, having about 20% and 15% lipids as oil droplets in cells.

Proteins: -represent less than 1% of the fresh mass of fruit and vegetable tissues. Leguminous
seeds are rich in protein, containing 15% to 30%. The proteins of fruits and vegetables are built
from amino acids, but other related simple nitrogenous compounds also occur.

Fresh fruits and vegetables are not important sources of protein. Most abundant protein source
are the Brassica vegetables which contain 3-5% and the legumes, which contain greater than 5%
protein. The protein is mostly functional, as in the form of enzymes, rather than acting as a
storage pool as in grains and nuts.

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Fiber: - One of the valuable indigestible components of fruits and vegetable. Dietary fiber
includes very diverse macromolecules exhibiting a large variety of physico-chemical properties.
The main components included as fiber are cellulose, hemicelluloses, pectins, lignin, resistant
starch and non-digestible oligosaccharides. Whole grains (especially the pericarp) and also fruits
and vegetables are considered very good sources of fiber. Fiber content of fruits and vegetables
is usually in the range of 1% to 3%. Several works have also associated diets rich in dietary fiber
with positive effects in disease prevention. Fiber passes through the digestive system, it imbibes
water which can calm the irritable bowel and, by triggering regular bowel movements, can
relieve or prevent constipation. The bulking and softening action of insoluble fiber also decreases
pressure inside the intestinal tract and so may help prevent diverticulosis (the development of
tiny, easily irritated pouches inside the colon) and diverticulitis (the often-painful inflammation
of these pouches).

Vitamins- are organic molecules required in trace amounts for normal development, which
cannot be synthesized in sufficient quantity by the organism and must be obtained from the diet.
The 14 vitamins known today are vitamin A (retinol), B complex [B1 (thiamine), B2 (riboflavin),
B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B9 (folate/folic acid), biotin, choline and
B12 (cyanocobalamine) and vitamins C, D, E and K. They do not have common functions or
structure and are usually grouped into fat-soluble (A, D, E and K) and water-soluble (B group
and C) molecules. The vitamins present in fruits and vegetables make an important contribution
to human nutrition, as they have specific functions in normal body performance (Table 1).
Vitamin A: Carotenoids are lipo-soluble pigments responsible for the yellow, orange and red
color of several fruits and vegetables. Vitamin A plays an important role in vision, cell division
and differentiation, bone development and reproduction. Vegetables that can supply useful
amounts of carotene include carrots, pumpkins and squashes. Compared to vegetables, fruits are
generally not as good a source of carotenoids, although there are a few notable exceptions such
as apricot, mango, citrus, papaya, watermelon, Tomatoes and peppers.

Sources of carotenoids

 Lycopene mainly in tomato and tomato products, water melon, pink grapefruit, papaya,
guava, rosehip

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  β-carotene in carrot, apricot, mango, red pepper, kale, spinach, broccoli
 α-carotene in carrot, collard green, pumpkin, corn, yellow pepper, cloudberry
 Lutein + zeaxanthin in corn, kale, spinach, broccoli, peas, Brussels sprout, collard green,
lettuce
 β-cryptoxanthin in avocado, orange, papaya, passion fruit, pepper

Vitamin B complex: -Thiamine is required in the human body for the metabolism of
carbohydrates. Green vegetables such as beans, beets, peppers and spinach are particularly rich
in riboflavin. Starchy vegetables and fruits are relatively poor sources of riboflavin. Niacin, also
known as nicotinic acid, is a precursor to NADH, NAD, NAD and NADP, which play essential
roles in living organisms. Almonds are a rich source, but no fruits or vegetables can be singled
out as being rich in niacin except perhaps, cape gooseberry and avocado. Niacin is relatively
stable. Symptoms of vitamin B 6 deficiency include dermatitis around the eyes, elbows and
mouth, along with soreness of the mouth and a red tongue. It can also lead to dizziness, vomiting,
weight loss and severe nervous disturbances Vitamin B 6 is present in appreciable amounts in
beans, cabbage, cauliflower, spinach, sweet potatoes, grapes, prunes, avocados and bananas.
Deficiency leads to depression, sleeplessness and muscle pains. Folic acid is essential for
reproduction and normal growth. It is present in fruits, spinach, cabbage and other green
vegetables. Lack of folic acid in the diet can cause a red tongue, diarrhea and anemia. Vitamin B
12 does not occur in fruits and vegetables.
Vitamin C: -Ascorbic acid (AsA) and its first oxidation product dehydroascorbic acid (which
can be reduced in the human body) might be considered as vitamin C. Ascorbic acid is a water-
soluble carbohydrate-derived compound showing antioxidant and acidic properties due to the
presence of a 2,3-enediol moiety. Humans and a few other species are not able to synthesize AsA.
AsA has crucial biological functions in humans, such as its participation in collagen biosynthesis.
Even though nutritional deficiencies are rare in modern western cultures, it is generally
recognized that dietary AsA also has important health benefits for the consumer, and an
increased intake of vitamin C has been associated with a reduced incidence of some diseases and
disorders. Vitamin C is present in fresh fruits and vegetables, as well as in fruit juices. Fruits,
particularly tropical species, and leafy vegetables are rich in ascorbic acid. Other good sources of

19
AsA include strawberry, kiwifruit, peppers, and citrus fruit, and spinach, broccoli and cabbage
among vegetables.
Functions of vitamin C in the human body:
 Facilitating the absorption of iron by reduction of ferric iron to ferrous iron
 Wound healing through stimulation of collagen synthesis
 Preventing cancer by acting as a free radical scavenger
 Involving in detoxification of histamine
 Proper functioning in the immune system

Deficiency causes
 Scurvy
 Poor wound healing and weak immune function
Vitamin E: -. Vitamin E levels are more abundant in oily seeds, olives, nuts, peanuts, avocados
and almonds. Even though the levels of vitamin E in broccoli and leafy vegetables are lower than
in fat-rich products, they are good sources compared to other fruits and vegetables. Vitamin E
deficiency results in stunted growth.
Vitamins D and K: -Vitamin D is a group of fat-soluble compounds. It occurs only in trace
amounts in fruits and vegetables. Vitamin K is essential for blood coagulation. It occurs
abundantly in lettuce, spinach, cauliflower and cabbage. As well as direct intake, it can also be
produced by bacteria in the intestines.

Minerals are normally classified as macro or micronutrients, based on the relative concentration
of each nutrient when those concentrations are adequate for normal tissue function.
Macronutrients include potassium (K), calcium (Ca), magnesium (Mg), nitrogen (N), and
phosphorus (P). Mineral micronutrients considered essential in human nutrition include
manganese (Mn), copper (Cu), iron (Fe), zinc (Zn), cobalt (Co), sodium (Na), chlorine (Cl),
iodine (I), fluorine (F), sulfur (S), and selenium (Se). In general, vegetables are a richer source of
minerals than fruits, but both vegetables and fruits are considered “nutrient-dense foods” in that
they provide substantial amounts of micronutrients, such as minerals and vitamins, but relatively
few calories. Inadequate levels of potassium intake have long been associated with higher blood
pressure. Potassium regulates heartbeat, assists in muscle contraction and is needed to send nerve

20
impulses and to release energy from fat, carbohydrates and protein. Potassium favorably affects
acid-base metabolism, which may reduce the risk of developing kidney stones and possibly
decrease bone loss with age. Although calcium intake is an important determinant in peak bone
mass, and in retarding bone loss in postmenopausal women, findings of higher bone mass and
lower bone resorption in women consuming high intakes of potassium, magnesium, zinc and
vitamin C emphasizes the importance of considering the impact of variation in other nutrients
when focusing on a particular mineral. Magnesium is also important in protein synthesis, release
of energy from muscle storage and body temperature regulation. Like the above mineral, it is
critical for proper heart function and plays a role in bone formation. Phosphorus also a primary
bone-forming mineral. The total mineral content present in fruit and vegetable is determined by
the ash value.
Besides eating more fruits and vegetables can also help lower cholesterol, Alzheimer’s and
Parkinson’s disease, obesity, diabetes, and control blood pressure. Low energy content of fruit
and vegetable facilitates maintaining a healthy weight, can be associated with a lower risk of
some chronic diseases especially cardiovascular diseases, including heart attack and stroke.
Generally, the intakes of fruit and vegetable are low in many developed and developing countries.
An increase of fruit and vegetable consumption would be appropriate especially for elderly
people because they are at greater risk for nutritional deficiencies as compared with younger
adults.
Even though fruit and vegetable rich sources of health benefit nutrient composition, they require
proper handling, preparation and storage in order to take full advantage of their many nutrients.
This is because the losses take place from harvest to consumption is substantial. For example,
changes take place is color, texture, flavor, and nutritional quality of many fresh fruits and
vegetables. To reduces the losses of nutritional quality of fruit and vegetable. Rinsing all produce
in potable water is the first important step. Even fruits and vegetables with skins, like bananas or
oranges, should be washed in order to remove any bacteria, pesticides or insects is important.
Soaking fruits and vegetables however should be avoided as water can dissolve a number of key
nutrients, like vitamin C.

2.4. Postharvest quality of fruit and vegetables

Quality itself includes aspects that are appealing to consumers, such as

21
  Appearance, aroma, taste, color (sensory), reduced risk of food borne pathogens or
pesticide residues (food safety), or more dense nutrient or phyto-nutrient content.

Growers and shippers realized that keeping produce cold greatly extended the sales life and this
stimulated much interest in exploring the causes of plant senescence at physiological, cellular,
and molecular levels. As consumers continue to increase their daily intake of fruits and
vegetables, pressure to deliver high-quality products with a longer shelf life is critical.

Quality characteristics in fruits, vegetables and other produce are those attributes that make
buyers or users want to buy them. These attributes may be physical that is they can be seen or
observed or by the fingers, others attributes are chemical and cannot be seen with the eyes or felt
between the fingers.
In fruits and vegetables, the physical or external attributes are: size, shape, colour, texture
compactness, uniformity, absence of defects, freshness and ripeness, gloss, firmness, flavor
and juiciness.
Size is often a major physical attribute considered and while producing you must have that
behind your mind. For most fruits and vegetables intermediate or average size is preferred. In
vegetables like okra, the size of the fruit indicates the quality; that is whether it was harvested
late or at the right time. Big fruits are often avoided as they would have become fibrous and such
are rejected by consumers. You can make the size of produce uniform by proper sorting.

Shape of the fruit is also a factor; sure you will turn down an orange fruit with oblong shape,
since naturally oranges are known to be roundish. Thus you will not want to do a thing that will
negatively affect the shape of the produce intended for marketing; say packaging in a tight
container. The natural shape of harvested produce can be maintained by proper packaging using
the ideal packaging material as well as not over stocking the container.
Colour is another physical attribute that is considered buy buyer is the colour. Fruits come in
different colours like red (e.g. some apple, tomato, and cashew), others are yellow examples
pawpaw, some oranges, plantain, and some have golden yellow colour. Whatever the case may
be, the consumer or buyer have an idea of what the acceptable colour is and he goes for produce
that meet his expectations.

22
 Colour is also an important attribute in vegetables. For example cucumber is valued green as
yellowness indicates over mature for consumption in other words it has gone past horticultural
maturity, The desired colour can be achieved by timely harvesting and handling as well as
choosing the desired variety.
Texture of a fruit describes how the fruit feels when examined by the fingers, the hand or the
mouth. It describes how soft, hard, tough or crispy. Other attributes associated with texture
include smoothness, hairiness or dryness.

This attribute is very important to the consumer when evaluating the quality of flowers and
vegetables that form heads like cabbage, lettuce or cauliflower. Loose head could be interpreted
by consumer to mean that the commodity was harvested prematurely. Also it is used to evaluate
freshness. Dehydration resulting from loss of moisture during display for sale will make the
heads to be loose and to the consumer that shows that the commodity has been harvested for long
and not really fresh. Dehydration or moisture loss must be controlled to make the produce as
compact as possible.

CHAPTER III

Physiology of Ripening of Fruits and Vegetables

Background

Basic important fact in post harvest handling of fruits and vegetables is that harvested fruits and
vegetables are living structures. They respire by taking up oxygen and giving off carbon dioxide
and heat. They also transpire i.e. lose moisture. While attached to plant, the losses due to
respiration and transpiration are replaced from the flow of sap having water, photosynthates
(mainly sucrose and amino-acids) and minerals. Respiration and transpiration continue after
harvest as well, because produce is now detached from the plant and devoid of normal source of
water, photosynthates and minerals, the produce is dependent entirely on its own food reserves
and moisture content. Therefore, losses of respirable substrates and moisture are not
compensated and deterioration starts; implying the perishable nature of fruits and vegetables.

3.1. Physiological Development

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 The lives of fruits and vegetables can be divided into three major physiological stages, growth,
maturation and senescence, after initiation or germination. However, there is no clear cut
distinction between these stages.

 Growth: involves cell division and subsequent cell enlargement, which accounts for the final
size of the produce.
 Maturation: usually starts before growth ceases and includes different activities in different
commodities. Growth and maturation are collectively referred to as development phase.
 Senescence: is defined as the period when anabolic (synthetic) biochemical processes give way
to catabolic (degradative) processes, leading to aging and finally death of the tissues.
 Ripening, a term reserved for fruit, is generally considered to begin during the later stages of
maturation and to be the first stage of senescence.
Development and maturation of fruit are completed only plant but ripening and senescence may
proceed on or off the plant. Fruits are generally harvested either when mature or when ripe.
Some fruits that are consumed as vegetable may be harvested even before the start of maturation
(e.g. cucumber, zucchini etc.).

Fruit Ripening is a dramatic event in the life of a fruit - transforming a physiologically mature
but inedible plant organ into a visually attractive olfactory and taste sensation. Ripening marks
the completion of development of a fruit and the commencement of senescence and it is
normally an irreversible event.

Growth Maturation Senescence

Ripening

Figure 1 Physiological development stages of Fruits and vegetables

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 Similar terminology is applied to the vegetables or to any determinant organ except that the
ripening stage does not occur, therefore, it is more difficult to delineate the change from
maturation to senescence in vegetables. Vegetables are harvested over a wide range of
physiological ages i.e. from a time well before the commencement of maturation through to the
commencement of senescence.

3.2. Changes that may occur during Ripening

A number of changes, which include synthesis and/or degradation of certain chemicals and
changes in physical/engineering properties, are known to accompany the ripening phase of fruits.
Some of these changes are:

1) Seed maturation
2) Color changes
3) Abscission (detachment from parent plant)
4) Changes in respiration rate.
5) Changes in rate of ethylene production.
6) Changes in tissue permeability
7) Softening( changes in composition of pectic substances)
8) Changes in carbohydrate composition
9) Organic acid changes
10) Protein changes.
11) Production of flavor volatiles
12) Development of wax on skin.

Physiology of Respiration

Respiration is a major metabolic process, taking place in harvested produce or in any living plant
product. It can be described as the oxidative breakdown of the more complex materials normally
present in cells e.g. starch, sugars or organic acids, into simpler molecules such as carbon
dioxide and water with the concurrent production of energy and other molecules which can be
used by the cell for synthetic reactions. Respiration can be aerobic or anaerobic sometimes called
fermentation.

25
 Respiration rate of produce is an excellent indicator of metabolic activity of the tissue and thus is
a useful guide to the potential storage life of the produce. If respiration rate of fruit or vegetable
is measured (as either O2 consumed or CO2 evolved) during the course of its development (i.e.
growth + maturation), maturation, ripening and senescence period, a characteristic respiratory
pattern is obtained. Respiration rate per unit weight is highest for the immature fruit or vegetable
and then steadily declines with age.
Climacteric and Non-climacteric Fruits and Vegetables

Most fruits (e.g. mango, banana, apple, tomato etc.) show a variation from the described
respiratory pattern in that they undergo a pronounced increase in respiration with ripening.
Such an increase in respiration, coincident with ripening is known as respiratory climacteric
and this group of fruit is known as the climacteric fruits.

The commencement of the respiratory climacteric coincides approximately with the attainment
of maximum size and it is during the climacteric that all the other changes characterizing
ripening occur. The respiratory climacteric as well as the complete ripening process may proceed
while the fruit is either attached to or detached from the plant.

Those fruits (e.g. citrus fruits, pineapple, strawberry etc.), which do not exhibit a respiratory
climacteric, are known as the non-climacterics fruits. These non-climacteric fruit exhibit most
of the ripening changes, although these usually occur more slowly than those of the climacteric
fruit. All vegetables can also be considered to have a non-climacteric type of respiratory
pattern (except tomato).

Presence of the respiratory peak is characteristic of climacteric fruit. A sharp increase in the
respiration is shown by the increase in production of carbon dioxide or decrease in internal
oxygen concentration. Fruits are grouped into two in this regard:
i. Climacteric fruits: such as apple, apricot, avocado, banana, Cherimoya, kiwi fruit, fig, mango,
Muskmelon, papaya, passion fruit, peach pear, persimmon, plum, watermelon, tomato, and so
on.
ii. Non-climacteric fruits: Blueberry, cherry (sweet and sour), Cucumber, grape, lemon, pineapple,
mandarin, strawberry, sweet orange, tree tomato and so on.

26
 Climacteric Non-climacteric

Respiration
Gas Production rate

rate

Growth

Ethylene production
Senescence

Cell Cell
Ripening
division enlargement
Maturation

Growth

Figure 2 Growth, respiration and ethylene production patterns of climacteric and non-climacteric
plant organs

4.1. Indices of Maturity and other Chemical Changes

The maturity of harvested perishable commodities has an important bearing on their storage life
and quality and may affect the way they are handled, transported and marketed. An
understanding of the meaning and measurement of maturity is, therefore, central to post harvest
handling of these perishable commodities.

27
Maturity is defined as that stage at which a commodity has reached a sufficient stage of
development that after harvesting and post harvest handling (including ripening where required);
its quality will be at least the minimum acceptable to the ultimate consumer.

Horticultural maturity is the stage of development when a plant or plant part possesses the
prerequisites for utilization by consumers for a particular purpose. A given commonality may be
horticulturally mature at any stage of development.

Physiological Maturity refers to a stage in the development of the fruit or vegetable when
maximum growth and maturation has taken place. It is usually associated with full ripening of a
fruit. (Physiologically mature stage is followed by senescence).

Estimating maturity- Among the different characters that have been used to establish maturity
are as follows:

Calendar date- For perennial fruit crops and fast rotation vegetables such as radish grown in
seasonal climates which are more or less uniform year to year, calendar date for harvest is a
reliable guide to commercial maturity e.g. days from planting or days from flowering. For some
crops, the chronological method is refined by calculating accumulated heat units during the
growing period which modulates the chronological index according to the weather pattern during
the growing reason.

Heat units An objective measure of the time required for the development of the fruit to
maturity after flowering can be made by measuring the degree days or heat units in a particular
environment. It has been found that a characteristic number of ‘heat unit’ or ‘degree days’ is
required to mature a crop. Under unusually warm conditions, maturity will be advanced and
under cooler conditions delayed.

The number of degree days to maturity is determined over a period of several years by obtaining
the algebraic sum of the differences, plus or minus, between the daily mean temperature and a

28
fixed base temperature (Commonly the minimum temperature at which growth occurs).The
average of degree days is used to forecast the probable date of maturity for the current year and
as maturity approaches, it can be checked by other means. This heat unit approach is helpful in
planning planting, harvesting and factory programs for crops such as corn, peas and tomato for
processing.
Physical Wide ranges of physical characteristics of commodities are used to assess their maturity.
They are:
(a) Size, Shape and Surface Characteristics- Changes in size, shape or surface characteristic of
fruits and vegetables are common maturity indices. Vegetables particularly, are harvested when
they have reached a marketable size. For banana maturity is determined as a change in diameter
of the figures, for some melons such as honey dew melons changes in surface gloss or feel
(waxiness) are used as maturity index.
(b) Abscission- During the later stages of maturation and start of ripening in many fruits, a
special band of cells, the abscission zone, develops on the stalk (pedicel) attaching the fruit to the
plant. Measurement of this zone, whose purpose is to permit the fruit to separate from the plant is
possibly the oldest of all maturity indices. It’s used to determine the maturity in the netted
muskmelon and is called as ‘slip’.
Color The color change which accompanies maturation in many fruits is widely used as a
maturity index. The loss of green color referred to as the ground color is a valuable guide to
maturity. There is initially a gradual loss of intensity of color from deep green to lighter green
and with many commodities, a complete loss of green with the development of yellow, red or
purple pigments.
The appearance of a trace of yellow at the apical end of papaya may be used to determine time of
harvest. Objective measurement of color is possible using a variety of instruments. Electronic
color sorting is also done for lemons and for tomato.
Texture As the fruits mature and ripen, they soften by dissolution of the middle lamella of the
cell wall. This softening can be estimated subjectively by finger or thumb pressure but a more
precise objective measurement, giving a numerical expression of flesh firmness is possible with a
fruit tester or penetrometer. Even the more elaborate machines such as the Instron Universal
Testing Instrument are also used but only for experimental studies.

29
Chemical changes- The maturation of fruits and vegetables is often accompanied by profound
changes in their chemical composition. The change in total soluble solids in extracted juice can
be measured using a refractometer and is used for melons, grape and citrus.

Conversion of starch to sugar during maturation is a simple test for the maturity of some apple
varieties. It is based on the reaction between starch and iodine to produce a blue or purple color.
The intensity of the color indicates the amount of starch remaining in the fruit. The sugar-acid
ratio is also used as maturity index for citrus.
Physiological changes- The maturation of commodities is associated with changes in their
physiology as measured by changing patterns of respiration and ethylene production. The
problem with using these parameters in assessing maturity is the variability in absolute rates of
ethylene production and respiration amongst similar individuals of the same commodity.
The concept of ‘green life’ has been developed to indicate the degree of physiological
immaturity at the time of harvest and also as a useful expression of potential post harvest life.
Green life is the time from harvest of the fruit to onset of ripening.
Chemical changes:
At one stage during the growth and development of fruits and vegetables, the produce is
recognized by the consumer as having attained optimum eating quality. This is not associated
with any universal change, but is attained in various ways in different tissues.
Fruit- Climacteric fruits generally reach the fully ripe stage after the respiratory climacteric.
Consumer associates other events initiated by ethylene also with ripening.
Color is the most obvious change that occurs in many fruits and is often the major criterion used
by consumers to determine whether the fruit is ripe or unripe. The most common change is the
loss of green colure on ripening (except avocado and Granny Smith apple). Many non-
climacteric fruits also exhibit a marked loss of green color with attainment of optimum eating
quality e.g. citrus fruits in temperate climate (but not in tropical climate).

The green color is due to the presence of chlorophyll, which is magnesium-organic complex. The
loss of green color is due to degradation of the chlorophyll structure. The principal agents
responsible for this degradation are post harvest changes (mainly due to leakage of organic acids

30
from the vacuole), oxidative systems and chlorophyllases. Loss of color depends on one or all of
the factors acting in sequence to destroy the chlorophyll structure.

The disappearance of chlorophyll is associated with the synthesis and/or revelation of pigments
ranging from yellow to red. Many of these pigments are carotenoids, which are unsaturated
hydrocarbons with generally forty carbon atoms and which may have one or more oxygen
functions in the molecules. Carotenoids are stable compounds and remain intact in the tissue
even when extensive senescence has occurred. These may be synthesized during the
development stage on the plant, but they are masked by the presence of chlorophyll. Following
the degradation of chlorophyll, the carotenoid pigments become visible (e.g. banana peel) while
in other commodities, carotenoid synthesis occurs concurrently with chlorophyll degradation (e.g.
tomato). Anthocyanins provide many of the red-purple color of fruits and vegetables.
Anthocyanin is water-soluble pigments.

Carbohydrates: The largest quantitative change associated with ripening is usually the
breakdown of carbohydrate polymers, particularly near total conversions of starch to sugar. This
has the dual effect of altering the taste and texture of the produce. The increase in sugar makes
the fruit much sweeter and therefore, more acceptable. Even with non-climacteric fruits, the
accumulation of sugar is associated with the development of optimum eating quality, although
the sugar may be derived from the sap imported into the fruit rather than from the breakdown of
starch reserves of the fruit.

The breakdown of polymeric carbohydrates, especially pectic substances and hemicelluloses,

weakens cell walls and the cohesive forces binding the cells together. In the initial stages, the
texture becomes more palatable, but eventually the plant structure disintegrates. Protopectin is
the insoluble parent form of pectic substances. Besides, being a large polymer, it is cross-linked
to other polymer chain with calcium bridges and is bound to other sugars and phosphate
derivatives to form an extremely large polymer. During ripening and maturation, protopectin is
gradually broken down to lower molecular weight fractions, which are more soluble in water.
The rate of degradation of pectic substances is directly correlated with the rate of softening of
fruit.

31
 Organic Acids: Usually organics acids decline during ripening as they are respired or converted
to sugar. Acids can be considered as a reserve source of energy to the fruit and would, therefore,
be expected to decline during the greater metabolic activities that occur on ripening. There are
few exceptions, such as banana and Pineapple, where the highest levels are attained at the full
ripe stage, but the levels in these fruits are not high at any stage of development compared to
other fruits.

Nitrogenous Compounds: Proteins and free amino acids are minor constituents of fruit and, as
far as is known, have no role in determining eating quality. Changes in nitrogenous constituents
do, however, indicate variations in metabolic activity during different growth phases. During the
climacteric phases of many fruits, there is a decrease in free amino acids which often reflects an
increase in protein synthesis. During senescence, the level of free amino acids increases
reflecting a breakdown of enzymes and decreased metabolic activity.

Aroma: plays an important part in the development of optimum eating quality in most fruits. It
is due to the synthesis of many volatile organic compounds during the ripening phase. These
compounds are called as volatiles. The total amount of carbon involved in the synthesis of
volatiles is less than 1 per cent of that expelled as CO2. The major volatile formed is ethylene
(accounting for 50-70% of the total carbon in the volatiles); ethylene does not contribute to
typical fruit aroma. Non-climacteric fruits also produce volatiles during the development of
optimum eating quality.

Factors affecting Respiration

The following eight points will highlight the eight major factors affecting aerobic respiration in
Plants. The eight environmental factors affecting the rate of respiration are:

1) Oxygen Content of the Atmosphere: The percentage of oxygen in the surrounding atmosphere
greatly influence the rate of respiration. But reduction of the oxygen content of the air, however,
causes no significant lowering in the respiratory rate until the percentage drops to about 10%. At
5% oxygen definite retardation of respiration occurs. With the increase of oxygen concentration

32
in the atmosphere, the rate of respiration also increases, but this effect is not as accelerating as
might be expected. On removal of oxygen the rate of respiration in terms of total carbon dioxide
produced actually increases. This indicates that anaerobic respiration comes into action when
oxygen is no longer available and that the plant, if it has to make up for the relative inefficiency
of this system, has to respire faster.

Figure 3. Effect of Concentration

2) Effect of Temperature

 It should be borne in mind that different plants or plant parts may show considerable
variation in regard to optimum temperature for respiration. The rate of respiration is
deeply influenced by temperature.
 Below 20 C and above 45 C the rate of respiration reduces.
 The optimum temperature for respiration is 20 C – 45 C.

3) Effect of Light: Light has indirect effects on the rate of respiration. With the increase in light
intensity, the temperature of the surrounding atmosphere also increases thus affecting the rate of
respiration. Secondly, the quantity of respirable material in the plant largely depends upon the
rate of photosynthesis which is directly influenced by light and thirdly, stomata remain open
during daylight and hence rapid exchange of gases takes place through them.

33
4) Effect of Water Contents: Over a certain range, water content of the plant tissue greatly
influence its rate of respiration. In most of the storage able seeds the moisture content is kept
below the point which allows a rapid respiration. With the increase in moisture content, the rate
of respiration is likely to go up with the result a rapid loss of viability will occur and at the same
time the temperature will also rise and the grain may be spoiled.

5) Effect of Respirable Material (Food Materials): Amount and kind of respirable material
present in the cells greatly affect the rate and course of respiration. It has been shown that plants
respire more rapidly after having been exposed to conditions favourable for photosynthesis
during which carbohydrates are synthesized. Increase in respiration has also been observed to be
associated with increase in soluble sugars.

6) Effect of Carbon Dioxide Concentration: The rate of respiration is normally not affected by
increase of carbon dioxide concentration in the surrounding atmosphere up to 19%, but as the
concentration increases from 10% to 80%, a progressive decrease in respiration occurs. Specific
response to higher CO2 concentration varies with the particular kind of tissue and plant. The
effect of CO2 concentration is more significant when the temperature and oxygen supply are low.
At a very high concentration of CO2 the plant tissues are injured or even killed.

7) Protoplasmic Conditions: The young growing tissues which have greater amount of
protoplasm as compare to older tissues, show higher rate of respiration. Their higher rate of
respiration supports the meristematic activities of the cells by supplying large amount of energy.
The degree of hydration of the protoplasm in the cells affects the rate, and mechanical injury to
plant tissues will accelerate respiration.

8) Other Factors: Various chemicals, such as cyanides, and fluorides, have been reported to
possess respiration retarding properties through their effect on respiratory enzymes. Respiration
rate may likely be accelerated by low concentrations of the compounds like ethylene, carbon
monoxide, chloroform and ether. Chlorides of various minerals, like sodium, potassium, calcium
and magnesium have pronounced effect on the rate of respiration. Monovalent chlorides, like
KCl and NaCl, increase the rate of respiration while the divalent chlorides, such as MgCl2 and
CaCl2 greatly reduce it.

34
 Chapter IV

The Role of Ethylene in Postharvest Horticulture

4.1. Effect of Ethylene

Climacteric and non-climacteric fruits may be further differentiated by their response to applied
ethylene and by their pattern of ethylene production during ripening. It is well known that all
fruits produce minute quantities of ethylene during development. However, coincident with
ripening, climacteric fruits produce much larger amounts of ethylene than non-climacteric fruits.
This difference between the two classes is further shown by the internal ethylene concentration
found at several stages of development and ripening.

Figure 3 Effects of applied ethylene on respiration patterns of climacteric and non-climacteric

fruits

35
The internal ethylene concentration of climacteric fruits varies widely, but that of non-
climacteric fruits changes little during development and ripening. Ethylene applied at
concentration as low as 0.1 - 1.0 micro liters per liter for one day, is normally sufficient to
hasten full ripening of climacteric fruits, but the magnitude of the climacteric is relatively
independent of the concentration of applied ethylene. In contrast applied ethylene merely
increases the respiration of non- climacteric fruits, magnitude of increase in respiration being
dependent on the concentration of ethylene. Moreover, the rise in respiration in response to
ethylene may occur more than once in non-climacteric fruits in contrast to the single respiration
increase in climacteric fruits.

4.2. Role of Ethylene

Methionine is the amino acid which is precursor of ethylene in plants. (Molecular O2 is needed
for the conversion; ethylene producing site or the organelle is still unknown and has not been
isolated from fruit tissues for in- vitro studies).

Applied ethylene will initiate the ripening of climacteric fruits and will cause some ripening-like
changes in non-climacteric fruits similar to those in senescing tissue. It is believed that ethylene
exercises hormonal type control over the fruit ripening process.
In some fruits like banana, avocado and melons, there is a small rise in endogenous (internally
produced) ethylene concentration preceding the commencement of the respiratory climacteric.
Other fruits e.g. mango and apple do not show this rise in internal ethylene concentration before
ripening. Once ripening has commenced, the large amount of ethylene synthesized by climacteric
fruit is thought necessary to promote all the aspects of ripening.

Many fruits as they develop and mature become more sensitive to ethylene. Early in the life of
fruit the concentration of applied ethylene required to initiate ripening is high and the length of
time to ripen is prolonged but decreases as the fruit matures. Banana and melons can be readily
ripened with ethylene even when immature but tomato is an extreme case of tolerance to
ethylene. (Nothing is known about the factor(s) that control the sensitivity of the tissue to
ethylene). There is no clear evidence suggesting the mechanism by which ethylene initiates and
controls fruit ripening and little is known about the site of action of ethylene and the mechanism
by which ethylene either promotes ripening or increase respiration in non-climacteric fruits.

36
Ripening has long been considered to be a process of senescence and to be due to a breaking
down of the cellular integrity of the tissue. Ripening is considered a phase in the differentiation
of plant tissue with altered nucleic acid and protein synthesis occurring at the commencement of
the respiratory climacteric.

4.3. Biosynthesis of ethylene

It has been proposed that two systems exist for the regulation of ethylene biosynthesis; system I
is probably involved in the regulation of senescence and system II is responsible for the
production of large amounts of ethylene during ripening, which is necessary for the full
integration of ripening. Non-climacteric fruits do not have an active system II and treatment of
climacteric fruits with ethylene circumvents system I.

Methionine

SAM synthase

SAM (S-adenosyl methionine)

AVG (Aminoethoxy Vinyle Glycine)

ACC synthase
AOA (Amino-oxy-acetic Acid)

ACC (1-amino cyclo-propane-1-carboxylic Acid)

Low O2 and Cobalt ion EFE (Ethylene Forming Enzyme)

Ethylene

Figure 4. Pathway of ethylene biosynthesis

37
Methionine, an essential amino acid, is considered to be the starting point for ethylene
biosynthesis. Methionine gives rise to S- adenosyl-methionine (SAM) and the reaction is
mediated by the enzyme SAM synthase. Then the SAM is converted to 1- aminocyclopropane-1-
carboxylic acid (ACC) which is now thought to be the immediate precursor for ethylene. ACC
synthase, the enzyme which controls the rate at which the pathway operates, is activated by a
common enzyme co-factor, pyridoxal phosphate. Inhibitors of enzymes that require pyridoxal
phosphate, such as aminoethoxy vinyl glycine (AVG) and amino oxyacetic acid (AOA) can be
used to inhibit ethylene production. ACC give rise to ethylene and this final step in the pathway
is mediated by ethylene forming enzyme (EFE). Cobalt ion and low O2 which inhibit the EFE
can also reduce ethylene production.

38
 CHAPTER V
5. Core Causes of Postharvest Losses and Manipulation of Environmental
Influences

Background

Fresh horticultural crops are diverse in morphological structure (roots, stems, leaves, flowers,
fruits, and so on), composition, and general physiology. Thus, commodity requirements and
recommendations for maximum postharvest life vary among the commodities. All fresh
horticultural crops are high in water content and are subject to desiccation (wilting, shriveling)
and mechanical injury. They are also susceptible to attack by bacteria and fungi, with
pathological breakdown. Biological (internal) causes of deterioration include respiration rate,
ethylene production and action, rates of compositional changes (associated with color, texture,
flavor, and nutritive value), mechanical injuries, water stress, sprouting and rooting,
physiological disorders, and pathological breakdown. The rate of biological deterioration
depends on several environmental (external) factors, including temperature, relative humidity, air
velocity, and atmospheric composition (concentrations of oxygen, carbon dioxide, and ethylene),
and sanitation procedures.

Wastage of fruits and vegetables by microorganisms during movement from harvest to

consumption can be rapid and severe, particularly in tropical areas where high temperature and
high humidity favor rapid microbial growth. Furthermore, ethylene produced by rotting produce
can cause premature ripening and senescence of other produce in the same storage and transport
environment and thus sound produce can be contaminated by rotting produce. Major post harvest
losses of fruits and vegetables are caused by species of the fungi (Alternaria, Botrytis, Diplodia,
Monilinia, Penicillium, Phomopsis, Rhizopus and Sclerotinia) and bacteria (Erwinia and
Pseudomonas). Most of them are weak pathogens and they can only invade damaged produce.

5.1. Temperature, Atmospheric Composition and Humidity.

Temperature is the most important environmental factor that influences the deterioration of
harvested commodities. Most perishable horticultural commodities last longest at temperatures

39
near 0ºC. At temperatures above the optimum, the rate of deterioration increases 2- to 3-fold for
every 10ºC rise in the temperature. Temperature influences how other internal and external
factors influence the commodity, and has a dramatic effect on the spore germination and growth
rate of pathogens. Temperatures outside the optimal range can cause rapid deterioration due to
the following disorders:

Chilling injury - Some commodities (mainly those native to the tropics and subtropics) respond
unfavorably to storage at low temperatures well above their freezing points, but below a critical
temperature (between 5 and 13°C depending on commodity and maturity stage) termed the
chilling threshold temperature or lowest safe temperature. Chilling injury is manifested in a
variety of symptoms including surface and internal discoloration, pitting, water soaking, failure
to ripen, uneven ripening, development of off flavors and heightened susceptibility to pathogen
attack.

Heat injury - High temperatures are also very injurious to perishable products. In growing
plants, transpiration is vital to maintaining optimal growth temperatures. Organs removed from
the plant, however, lack the protective effects of transpiration, and direct sources of heat, for
example full sunlight, can rapidly heat tissues to above the thermal death point of their cells,

leading to localized bleaching or necrosis (sunburn or sunscald) or general collapse.

Relative Humidity (RH) is the moisture content (as water vapor) of the atmosphere, expressed
as a percentage of the amount of moisture that can be retained by the atmosphere (moisture
holding capacity) at a given temperature and pressure without condensation. The moisture
holding capacity of air increases with temperature. Water loss is directly proportional to the
vapor pressure difference (VPD) between the commodity and its environment. VPD is inversely
related to RH of the air surrounding the commodity. RH can influence water loss, decay
development, incidence and severity of some physiological disorders, and uniformity of fruit
ripening. Condensation of moisture on the commodity (sweating) over long periods of time is
probably more important in enhancing decay than is the RH of ambient air. An appropriate RH
range for storage of fruits is 85 to 95% while that for most vegetables varies from 90 to 98%.
The optimal RH range for dry onions and pumpkins is 70 to 75%. Some root vegetables, such as
carrot and radish, can best be held at 95 to 100% RH. RH can be controlled by one or more of

40
the following procedures: (1) adding moisture (water mist or spray, steam) to air by humidifiers;
(2) regulating air movement and ventilation in relation to the produce load in the cold storage
room; (3) maintaining temperature of the refrigeration coils within about 1ºC of the air
temperature; (4) providing moisture barriers that insulate walls of storage rooms and transit
vehicles; (5) adding polyethylene liners in containers and using perforated polymeric films for
packaging; (6) wetting floors in storage rooms; (7) adding crushed ice in shipping containers or
in retail displays for commodities that are not injured by the practice; and (8) sprinkling produce
with sanitized, clean water during retail marketing of commodities that benefit from misting,
such as leafy vegetables, cool-season root vegetables, and immature fruit vegetables (such as
snap beans, peas, sweet corn, and summer squash)

Atmospheric composition: Respiration is the basic process causing deterioration on the

harvested produce and is mainly depend on the atmospheric composition (level of O2 and CO2)
as well as on the temperature, ethylene and water vapor. Therefore, regulating the gas
concentrations in the surrounding atmosphere of the produce is highly important for reducing
respiration and increasing preservation time. Reduction of O2 and elevation of CO2 can delay
deterioration of fresh horticultural crops. However, it is highly depended on the type of
commodity, cultivar, maturity, and temperature. Modified atmosphere packaging (MAP) is a
useful system which makes it possible to regulate the composition of the atmosphere in the
packaging headspace. During respiration, O2 is consumed, and CO2, ethylene, and water vapor
are generated, thus the packaging material allows the transfer of all of these gasses through the
packaging material by regulating the inner composition at favor‐able levels to preserve the
produce. MAP slows down respiration and other metabolic processes, reduces sensitivity to
ethylene, reduces the development of some physiological disorders i.e. chilling injury and may
inhibit pathogen development.

5.2. Mechanical injuries

Mechanical damage is caused by inappropriate methods used during harvesting, packaging, and
inadequate transporting, which can lead to tissue wounds, abrasion, breakage, squeezing, and
escape of fruits or vegetables. Mechanical damage may increase susceptibility to decay and
growth of microorganisms. Some operations, such as washing, can reduce the microbial load;

41
however, they may also help to distribute spoilage microorganisms and moisten surfaces enough
to permit growth of microorganisms during holding periods. Harvesting methods cause bruising
and damage to the cellular and tissue structure, in which enzyme activity is greatly enhanced as
cellular components are dislocated.

Besides the above issues, most 'post-harvest losses in developing countries occur during
transport, handling, storage, and processing. Rough handling during preparation for market will
increase bruising and mechanical damage, and limits the benefits of cooling.

5.3. Physiological disorders

Physiological disorders of vegetables and fruits originated from inexpedient environmental

conditions during the post and pre-harvesting periods. Lower temperatures can also create
respiratory or nutritional disorders in harvested produce. Inappropriate temperatures may
aggravate the typical metabolism of the preserved products. Chilling injury is caused by low
temperatures, i.e. <10−13°C. Chilling injury to plants produce potential symptoms such as
lesions on the surface, discoloration of internal and external tissue, accelerated decay, water-
soaking of tissues and abnormal ripening. The manifestations of Chilling injury may not be
obvious while the produce is held at chilling temperature; however, it is observable subsequent
to being moved to room temperature. Freezing injury occurs because of keeping the products
below their frigid temperatures. Ice crystals are formed in very low temperature which
breakdown the tissues and thus cause the total loss of the produce. Calcium is related to more
postharvest-related insufficiency issues than some other minerals. Harsh pit of apples and bloom
end decay of tomato are notable calcium lack symptoms in horticultural crops. Respiratory issues
are related to exceptionally low O2 (20%) concentrations in or around harvested produce in
packaging/storage condition.

5.4. Postharvest diseases

Postharvest diseases: Stored products are subject to a variety of rots and decay caused by fungi
or bacteria. Most known fungus are Penicillium expansum, Botrytis cinerea, Alternaria alternata,
Rhizopus stolonifer, Phytophthora infestans and Fusarium spp and the bacteria are Ervinia
carotovora and Pseudomona spp. These diseases might cause light brown and soft spots on fruits

42
and vegetables. Infection of diseases may start before or after harvest. When products transferred
to storage, infections continue to develop. Mechanical damages, wounds or bruises are known to
be the common entry points for bacteria and fungi. To prevent postharvest diseases, careful
monitoring and management of diseases need to be started during growing period and continue
in the storage. Preventing mechanical damage and harvesting the products during the cool times
of the day are crucial points. Pre-harvest and postharvest application of suitable fungicides,
bactericides might be helpful in managing disease problems. However, it must be kept in mind
that environmental conditions are highly important for the development of diseases. They usually
require warm temperatures and high moisture. On the other hand, sanitation is of utmost
importance for handler’s notonly to protect products from postharvest diseases but also to protect
consumers from food borne illnesses which caused by Escherichia coli and Salmonella. On the
other hand, there are some environmental factors (temperature, relative humidity, atmospheric
composition, and light) which accelerate or retard deterioration by directly or indirectly
influencing biological factors.

43
 CHAPTER VI

6. Postharvest Handling Technologies

6.1. Cooling and Cold Storage of Fresh Fruits and Vegetables

A cold chain for perishable foods can be defined as the uninterrupted handling of the
product within a low-temperature surrounding during the postharvest steps of the value chain.
After harvest, a food cold chain pathway includes pre-cooling, bulk storage, distribution, retail
cooling and household refrigeration before consumption. Although a cold chain does not
necessarily have to include all of the aforementioned steps, it must involve at least one of these
steps. This section provides an overview of pre-cooling and bulk storage methods for fresh fruits
and vegetables.

Bulk cold storage refers to the storage of (large) quantities of produce after production and
initial post-production handling. Bulk cooling may take place on farms, at production facilities,
at collection/grading centers or at processing facilities. Pre-cooling of products prior to bulk
cooling is necessary in order to achieve desired temperature reductions faster than direct
integration into bulk storage. Cooling and cold storage require enough starting capital and
running costs and reliable electricity supply. These preconditions are often not available to
farmers in developing countries. Hence, small-scale farmers have no access to unbroken cold
chains and the use of sustainable cold storage facilities.

In general, improving cold storage in food value chains provides significant development
benefits, such as expanding access to suitable infrastructures and strengthening local
management capacities. It also offers environmental protection by reducing waste and carbon
emissions, providing efficient use of natural resources and accelerating economic growth through
energy and cost savings and increased incomes to rural farmers.

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 Pre-cooling Methods

The temperature of fruit and vegetables at harvest is close to that of ambient air and could be as
high as 400 C. At this temperature respiration rate is extremely high and storage life is short. (It is
advised to harvest early in morning as the lower temperature prevails at that time). Quicker the
temperature of the produce is reduced to the selected storage temperature the longer will be its
storage life.
Rapid cooling after harvest is generally referred to as Pre-cooling. It removes the field heat and
is essential for fruit and vegetables as refrigerated containers are not designed to handle the full
load of field heat, but are designed to merely maintain pre-cooled produce at the selected
temperature. Pre-cooling as a wider term includes any cooling treatment given to produce before
shipment, storage or processing but a stricter definition of Pre-cooling would include only those
cooling methods by which the produce is cooled rapidly and certainly within 24 hours of harvest.
The selection of the Pre-cooling method depends on three main factors:
a) The temperature of the produce at harvest
b) The physiology of the produce
c) The desired post harvest life

The commodities which are to be cured i.e. thickening of periderm by drying in shade at
temperatures above those required for extended storage is not normally pre-cooled e.g. potato,
sweet potato, yam.
Methods of Pre-cooling: Commodities may be cooled by means of cold air (room cooling,
forced air cooling), cold water (hydro cooling), direct contact with ice and evaporation of water
from the produce (evaporative cooling, vacuum cooling).

Room cooling It is the most common cooling method where produce in boxes, cartons, bulk
containers or other packages is exposed to cold air in a cool store. For adequate cooling, air
velocities around the packages should be at least 60 meters per minute. Room cooling is
relatively slow and thus may be inadequate for more sensitive commodity. It removes heat only
from the surface of the package, the size and shape of the package being the limiting factor.

Forced air (pressure) cooling- The rate of cooling with cold air may be significantly increased
if the heat transfer surface is enlarged from that of package to the total surfaces of the produce.

45
In forced air cooling, air is forced through the packages and around each piece of produce as a
result cooling is faster. It can cool the commodity in about one forth to one tenth of the time
required for room cooling.

Hydro cooling is a rapid method for cooling in which water acts as the heat transfer medium. It
is rapid if the water contacts most of the surface of the produce & is maintained as close to O0C
as possible. In many hydro cooling systems, the produce passes under cold showers on a moving
conveyor. Hydro cooling may also clean the produce but chances of contamination of the
produces with spoilage causing microorganism are also there.

Contact-Icing- Before the advent of some of the modern Pre-cooling methods, contact or
package icing was used extensibly for Pre-cooling the produce & maintaining temperature during
transit, especially for highly perishable commodities such as leafy vegetables. Contact icing is
now mainly employed as a supplement to other forms of Pre-cooling. The finely crushed ice or
an ice slurry (liquid ice i.e. 40% water + 60 per cent ice + 0.1 per cent salt) is sprayed on to the
top of the load inside the road or rail transit vehicle. This is often referred to as top icing.

Vacuum Cooling is mostly used for the vegetables that have a high surface to volume ratio
such as leafy vegetables. They can be cooled rapidly & uniformly by boiling off some of their
water content i.e. moisture at low pressure. The produce is loaded into a sealed container and the
pressure is reduced to about 660 Pascals (5mm mercury). At this pressure water boils at 10C and
the produce is cooled by evaporation of water from the tissue surface. For every 50C drop in
temperature, approximately 1 per cent of the produce weight is boiled off as water. This weight
loss may be minimized by spraying the produce with water either before enclosing it in the
vacuum chamber or towards the end of the vacuum cooling operation which is referred as
hydro-vacuum cooling. The rate of cooling by this method is largely dependent on the surface
to volume ratio of the produce and the ease with which the produce loses water. Leafy vegetables
are ideally suited to vacuum cooling and asparagus, broccoli, Brussels sprout, mushroom &
celery can also be vacuum cooled. Fruits are having a low surface to volume ratio and a waxy
cuticle, so loss of water is slow and do not benefit vacuum cooling.

46
Evaporative cooling- In this method, commodity can be cooled by either blowing the
humidified cool air or by misting with water and then blowing dry air over the wet fruit. This
Method is restricted to regions having climate with low relative humidity but with a good quality
water supply. It has the advantage of being low cost cooling method in which dry air is cooled by
blowing it across a wet surface.

6.2. Packaging
The function of a package is primarily to contain and protect the produce. With fresh fruits and
vegetables there are often two levels of packaging. The first is the pack in which the produce is
offered to the consumer. The second is the pack that contains the consumer pack and is used to
transport the product to the retail market. The size of the package is therefore important.

The use of standard pallets is increasing and the package may have to be designed to fit these or
to fit a standard refrigerated container. Fresh fruit and vegetables being living organisms give out
heat and gases that can be detrimental if allowed to accumulate in the package so they may need
to be ventilated. Certain types of packaging can be used to extend the storage life of crops, such
as using plastic films to modify the atmosphere around the crop, or to protect it from infection or
infestation. Root crops can be packed into material such as coir dust, peat or even sawdust to
protect them and provide a humid environment.

Bags and sacks

Most fruits and vegetables are harvested and placed in a container for transport to a pack house
or directly into a store. In many cases the crop is packed into a container in the field, and it stays
in the same container right through to the wholesale market or even the retail market. The
advantages of this are that the crop is handled only once so the potential for causing mechanical
injury to it is reduced. Also, handling takes time and labour, both of which can be expensive. The
amount packed in each bag is important. If a bag is too heavy the contents are more likely to be
damaged.

Baskets are traditional containers into which crops are placed at harvest. They have been used in
most countries and are of a variety of designs. They are usually made from split bamboo, rattan
or palm leaves that are woven to form traditional-shaped con tainers and are usually conical in

47
shape, or if they are squarish or rectangular they tend to have sloping sides and rounded corners
because of the way in which they are made. Construction is normally by hand and often.

Baskets may be made from cheap materials, but these have poor stacking strength and when
placed on top of each other the weight of the baskets is taken by the produce and not by the
basket, which may lead to damage to the crop due to compression.

Wooden field boxes were made from thin pieces of wood bound together with wire and were of
two sizes, the bushel with a volume of 2200 cubic inches and the half-bushel box. They had the
advantage that they could be packed flat when empty and were inexpensive so they could be
non-returnable. However, they provided limited protection from mechanical damage during
transport.
Plastic field boxes
These are recyclable and are used many times because they are strong and durable. Many are
designed in such a way that they can nest inside each other when empty, to facilitate transport,
and stack one on top of another when full. Plastic boxes are strong, have good stacking strength
and, if correctly made, a smooth surface. This means that they give good protection to the
produce during handling and transport. They are completely water resistant and therefore easy to
keep clean. They tend to be expensive and therefore each box has to be used many times to make
them economic. If a suitable system can be devised for returning the boxes to the field from the
market, plastic boxes can provide a very economical system for crop handling. Some plastic
boxes produced in large quantities can be used for single journeys for high value crops.
Expanded polystyrene boxes have been used for many years for non-returnable transport of crops
such as watercress.

Pallet boxes
The size of pallet boxes can vary but they are most commonly based on the standard size for a
European pallet of 1 × 1.2 m and the are usually about 0.5 m high. These have a capacity of
about 500 kg depending on the crop that they contain. They are made from wood or plastic and
are used for a whole range of crops. The produce is commonly loaded into them in the field and
they are then transported directly to the store or pack house.

48
Fibre-board boxes
These are made from either laminated fibreboard or, more commonly, corrugated fibreboard.
They may be used for transporting produce from the field to the packhouse, in which case the
same carton may be used on several occasions. Corrugated cartons used for transporting yams
from the field to the pack house could be economic because of reduced injury to the tubers even
when the cartons were used only once.
Fiber board boxes are made from either wood pulp or recycled paper, although other materials
have been used. Other non-wood pulps have been made from bagasse, bamboo, straw, etc. The
softwood pulp. The Kraft can be described as virgin where the fibers are processed straight from
the tree, or recycled where they have been obtained from waste paper, fiber board boxes.

6.3. Preservation and processing

Curing
Curing is an effective operation to reduce the water loss during storage from hardy vegetables
viz, onion, garlic, sweet potato and other tropical root vegetables. The curing methods employed
for root crops are entirely different than that from the bulbous crops (onions and garlic). The
curing of root and tuber crops develops periderms over cut, broken or skinned surfaces wound
restoration. It helps in the healing of harvest injuries, reduces loss of water and prevents the
infection by decay pathogens. Onions and garlic are cured to dry the necks and outer scales. For
the curing of onion and garlic, the bulbs are left in the field after harvesting under shade for a
few days until the green tops, outer skins and roots are fully dried.
Waxing
Quality retention is a major consideration in modem fresh fruit marketing system. Waxes are
esters of higher fatty acid with monohydric alcohols and hydrocarbons and some free fatty acids.
But coating applied to the surface of fruit is commonly called waxes whether or not any
component is actually a wax. Waxing generally reduces the respiration and transpiration rates,
but other chemicals such as fungicides, growth regulators, preservative can also be incorporated
specially for reducing microbial spoilage, sprout inhibition etc. However, it should be
remembered that waxing does not improve the quality of any inferior horticulture product but it
can be a beneficial adjunct to good handling. The advantages of wax application are: - Improved
appearances of fruit. - Reduced moisture losses and retards wilting and shrivelling during storage

49
of fruits. - Less spoilage specially due to chilling injury and browning. - Creates diffusion barrier
as a result of which it reduces the availability of 02 to the tissues thereby reducing respiration
rate. - Protects fruits from micro-biological infection. - Considered a cost effective substitute in
the reduction of spoilage when refrigerated storage is unaffordable. - Wax coating are used as
carriers for sprout inhibitors, growth regulators and preservatives. The principal disadvantage of
wax coating is the development of off- flavour if not applied properly. Adverse flavour changes
have been attributed to inhibition of O2 and CO2 exchange thus, resulting in anaerobic
respiration and elevated ethanol and acetaldehyde contents. Paraffm wax, Carnauba wax, Bee
wax, Shellac, Wood resins and Polyethylene waxes used commercially.

6.2. Transportation
Transport of the produce can be affected as follows: Field and farm transport.
 Routes for the movement of produce within farm fields should be planned before crops
are planted.
 Farm roads should be kept in good conditions because great damage can be inflicted on
produce carried over rough roads in unsuitable vehicles.
 Containers must be loaded in the transport vehicle carefully and stacked in such a way
that they cannot shift or collapse, damaging the content.
 Vehicles need good shock absorbers and low-pressure tires and must move with care.
Transport from the farm.
 Usually produce is graded and packed in the field for small local market.
 A commercial packing house. Produce may be in palletized field containers or in hand
loaded sacks or wooden or plastic boxes. In the packing-house the produce is graded and
packed in suitable containers for the market.

6.3. Methods of Storage

In-ground storage: Pit storage or clamp storage is used for storing hard vegetables e.g. potato,
turnip and late season cabbage. They are piled into the pit, which is dug into a hillside or other
well drained spot. The pit is lined with hay or straw; the produce is then covered with straw
followed by 10 to 20 cm of sods and earth to protect it a gains freezing and rain. Piped
ventilation to the outside is provided to avoid the respiratory self-heating. Clamp storage has

50
been suitable only for storage of hard vegetables in cold winter climates and is also suitable for
storage of cassava for up to two months in the tropics.

Cellars are more sophisticated forms of below-growled storage; they may be part of above
ground building or underground rooms, often in hillsides, where access is easier. The
performance of cellar is improved by providing controlled ventilation openings for entrance of
cold air and exit of warm air by convectional circulation when cooling is required. A good cellar
will provide satisfactory storage for hard vegetables and long keeping fruits e.g. apple.

Air-cooled stores- These are simply insulated structures above ground or partly underground,
which are cooled by circulation of colder, outside air. When the temperature of the produce is
above the desired level, and if the temperature of the outside air is lower, air is circulated through
the stack in the store by convectional or mechanical means through bottom inlet vents and top
outlets with dampers. Fans, if fitted, are controlled manually, or automatically which differential
thermostats. The air may be humidified, a process that can also be automated. Air-cooled stores
are widely used for the storage of potato and sweet potato which need relatively high storage
temperature to avoid accumulation of sugar & chilling injury respectively. Potatoes are
commonly stored in bulk piles in stores with air delivery ducts under the floor or at floor level,
and with suitably spaced air outlets.

Ice- Refrigeration- The use of natural ice as a refrigerant was an advance on air-cooled storage.
The lower temperature obtained by ice refrigeration enabled longer storage of meat & other
perishable commodities. Ice was harvested in winter from frozen lakes & ponds and stored in
insulated ‘ice houses’. The melting of 1kg of ice absorbs 325 kilojoules, but the considerable
bulk of ice needed and disposal of the melted water are disadvantages. The introduction of the
small ‘ice box’ or ‘ice chest’ is useful in commercial preservation of perishable foodstuffs.

Fans are usually necessary to circulate the storage air over the cooling coils of the evaporator and
through the stacks of produce in the store. Moving air is the main agent for transfer of heat from
the contents of the store and from leakage into the store, to the coils; radiation and convection
may play a small part.

51
In addition to these three basic components of a refrigeration plant and fans or correctly placed
air ducts, several other items are required such as items of ancillary control equipment, a liquid
receiver and some means of defrosting the coils.

Controlled Atmosphere (CA) or Modified Atmosphere (MA) Storage

Controlled atmosphere or modified atmosphere means removal or addition of gases into the
storage room resulting in an atmospheric composition around the commodity which is different
from that of air (78.08% N2, 20.95%02, 0.03% CO2). Usually this involves reduction of oxygen
and/or elevation of carbon dioxide concentrations. CA & MA differ only in the degree of control;
CA is more exact i.e. gas concentrations are precisely controlled in CA. We can say, All CA
storage are MA storage but all MA storage may not be CA storage.

Controlled atmospheric (CA) storage utilizes low oxygen and high carbon dioxide concentration
to slow down the ripening processes, stop the development of some storage disorders e.g. scald
in apple and to reduce the growth of decay organisms. All of these effects extend storage life of
fresh produce compared with refrigerated air storage. CA storage has all the design requirements
of conventional refrigerated storage plus gastight rooms, equipment to obtain desired gas
concentrations and equipment to measure and control atmospheric composition.

Gas-tight construction: Three main types of interior wall and ceiling construction are used for
CA storage.

1) Foamed-in-place urethane over concrete or steel wall

2) Plywood- covered stud walls with fiberglass insulation
3) Insulated, metal covered panels

Pressure Relief- A pressure difference between the CA store room and the outside can develop
because of changes in weather or room temperature. This difference can damage the gas seal if it
is not relieved. A water trap is usually used to allow pressures to equalize. The trap is filled with
glycol to avoid problem with the water evaporating. A spring- loaded or weight- loaded check
valve can be used but are much more expensive than a water trap.
Ten square cm (10cm2) of vent opening should be provided for each 40m3 of room volume
(1in2 per 1000Ft3)

52
Small changes in pressure can be relieved by using breather bags. These have the advantage of
capturing the gas mixture in the room and allowing it to re-enter the room at a later time. Bags
should have 0.35 to 0.4 m3 of capacity per 100m3 of room volume (3.5-4.0ft3/1000ft3).

If a CA room is so tightly sealed that air must be regularly bled into the room to maintain O2
level, breather bags are not necessary.

Atmosphere modification: The least expensive, but slowest method of modifying the storage
room atmosphere is to let the product do it through natural respiration.

Bags of hydrated lime are used to aboard excess CO2. Lime requirements are 1 to 3kg per 100 kg
of product depending up on the product being stored, storing time, surface area and quality of the
lime. Bags can be placed either in single layers in CA room or in an adjacent lime room that is
connected to the CA room with a fan and duct work. Rooms should be sized to hold about 15kg
of lime per metric ton of product. Lime is very effective in creating low levels of CO2 and is
being used extensively. CO2 levels can also be controlled with activated carbon adsorption
systems, molecular sieves or brine pumped over evaporator coils.

For controlling O2 level in CA room, CA room is purged with N2 in liquid form or produced on
site. One types of N2 generator uses ammonia in a combustion process to consume O2 and
produce N2 & water. Other system uses a separator that circulates air through a molecular sieve
beds or semi permeable membrane system or by a purge system where fresh air has its O2
reduced in the generator then fed into the room. O2 or CO2 levels must be monitored daily to
ensure that they are within prescribed limits. Automatic equipment is widely used for it. A
minimum of two calibrated dial thermometers should be installed in each room for monitoring
temperature regularly. Electronic thermometers are also used.

Safety considerations: The atmosphere in CA room will not support human life and people have
died of asphyxia while working in CA rooms without breathing apparatus. A danger sign should
be posted on the door. The access room in the door should be large enough to accommodate a

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person equipped with breathing equipment. At least two people with breathing equipment should
work together at all times, one inside and one outside the room watching the first person.

Ethylene Removal- Use of the ethylene absorbers, such as potassium permanganate alone or in
combination with activated and brominated charcoal can be used for ethylene removal in CA
storage.
Hypobaric or Low Pressures Storage (LPS)
Reducing the total pressure (under partial vacuum conditions) results in reducing the partial
pressures of individual gases in air. This can be an effective method for reducing O2 tension, and
for accelerating the escape of ethylene & other volatiles.

Advantages of LPS-
 It offers more exact control of O2 concentration that permit the use of lower O2 tension
than is possible with CA.
 It facilitates removal of ethylene and other volatiles.

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