Lesson Module for Postharvest Technology 1
Title: Regulation of Ripening
Topic 9: Methods of Ripening and Slowing Down of Ripening
Time Frame: 10 hours (4 hours lecture and 6 hours laboratory)
Introduction:
Ripening is the process by which fruits attain their desirable flavour, quality, colour, palatable
nature and other textural properties. Ripening is associated with change in composition i.e.
conversion of starch to sugar. On the basis of ripening behavior, fruits are classified as
climacteric and non-climacteric fruits.
Climacteric: Climacteric fruits are defined as fruits that enter ‗climacteric phase‘ after harvest
i.e. they continue to ripen. During the ripening process the fruits emit ethylene along with
increased rate of respiration. Ripe fruits are soft and delicate and generally cannot withstand
rigours of transport and repeated handling. These fruits are harvested hard and green, but
fully mature and are ripened near consumption areas. Small dose of ethylene is used to
induce ripening process under controlled conditions of temperature and humidity.
Non-Climacteric: Non-climacteric fruits once harvested do not ripen further. Non-climacteric
fruits produce very small amount of ethylene and do not respond to ethylene treatment.
There is no characteristic increased rate of respiration or production of carbon dioxide.
(agritech.tnau.ac.in)
Objectives:
describe the mechanism of ripening, and the factors affecting ripening
demonstrate some methods of hastening ripening of fruits and some methods of delaying
ripening of fruits
evaluate the efficiency of indigenous and commercial ripening inducers
Pre – Test:
Activity:
Divide yourselves into five groups. Each group will obtain three bunches of green mature
banana fruits. Dehand the bunches and divide the fruits into six. Place banana hands in a
basket / carton lined with newspaper. Each group should perform the treatments below.
Ripening induction treatments:
1. control – no treatment
2. madre de cacao leaves – place 250 gram at the bottom of the basket
3. squash peelings – place 250 grams at the bottom of the basket
4. passion fruit - place at the center of the fruits
5. calcium carbide – wrap in newspaper five gram of calcium carbide and
place at the bottom of the basket
6. ethrel (1,000 ppm) – soak the banana hand and allow to dry before
placing fruits in a basket
Table1. Ripening behaviour of banana fruits in response to different ripening inducers
Treatments No. of days to % ripening Weight loss Other
ripening Observations
1. control
2. madre de
cacao
3. squash
peelings
4. passion
fruit or
substitute
5. calcium
carbide
6. ethrel
Number of days to ripening is obtained by counting the number of days from start of
treatment up to the time 90% of the fruits or fingers reach the yellow color.
Percentage ripening is computed by:
no. of fruits that ripened
% ripening = ---------------------------------- x 100
Total no. of fruits treated
Weight loss is computed by:
Weight loss = initial weight – final weight
Learning activities include content / discussion of the topic:
RIPENING OF FRUITS
Ripening is the process by which certain fruit develops all its characteristics. The fruit usually
becomes soft, less acidic, sweet and aromatic. It also changes in color and loses its
astringency or its unpleasant biting taste.
Ripening can be accelerated depending on the type of fruits whether climacteric or non –
climacteric. Climacteric fruits are those that can be picked mature green and ripened after
harvest. Such fruits undergo further color and flavour development after harvest. The non –
climacteric fruits are those that have to be picked ripe and ready to eat as they do not
undergo further ripening, color and flavour development when harvested unripe.
The process of ripening in fruits is generally triggered by ethylene (C 2H4) which is known as
the senescence and ripening hormone. This hormone has been shown to act like a switch to
trigger changes associated with ripening. As the fruit matures, it produces a small amount of
ethylene until it reaches a critical concentration that can stimulate more production of
ethylene. Such phenomenon is called the autocatalytic production of ethylene. Aside from
endogenous ethylene (prodiced fro the fruit tissue), exogenous (external) ethylene can also
be applied to fruits from ethylene – releasing compounds or other sources of ethylene.
Another compound chemically related to ethylene which can act like ethylene to trigger
ripening is acetylene (CaC2), popularly known as ―carburo‖.
ADVANTAGES OF ACCELERATED RIPENING
1. Allows shipment of fruit at mature green stage. Ripe fruits are more susceptible to
damage. Transporting them mature green reduces the risk of mechanical damage
during transit.
2. Insures maximum and uniform color development. Usually, when ripening is
accelerated conditions for ripening are regulated to approach optimum, so maximum
and uniform development of color is assured.
3. Allows development of fruits to an acceptable marketable color ahead of disease
symptom development.
4. Minimizes shrivelling. Allowing fruits to ripen at ambient temperature takes a long
time and water loss becomes great.
5. Faster means of getting cash or faster turn – over of capital. Accelerated ripening
also allows the seller to dispose more fruits during a given time instead of waiting for
the fruits to ripen naturally.
6. Take advantage of high price during early, late or off – season, or when the supply is
low such as after the typhoon.
7. Provides wholesalers or retailers flexibility in selling the fruit.
8. More efficient use of warehouse space. Limited warehouse space would be best
utilized by disposing of commodities as fast as possible. Therefore, fruits should be
ripened at the fastest possible rate without sacrificing quality.
Methods of Accelerating Ripening
1. Introduce ethylene and/or acetylene in the environment of the fruit
2. Induce the fruit to produce stress ethylene as in wounding of fruit.
3. Expose fruits to bio ethylene or ethylene from high – ethylene producing leaves or
fruits.
4. Increase the temperature of the fruits up to a certain point to accelerate changes in
fruit. With increase in temperature, ethylene production of the fruit is expected to
increase.
5. Use of smoke (smoking) as Source of ethylene and acetylene.
SLOWING DOWN RIPENING / DELAYING RIPENING
Delaying or slowing down ripening is one of the methods of extending the green life
or prolonging the storage life of fruits. This is also very beneficial and advantageous
especially when fruits are intended for long distant transport or export purposes.
METHODS OF SLOWING DOWN RIPENING
1. Exclude ethylene and acetylene from the immediate environment of mature green
fruits.
2. Use of ethylene absorbents such as the use of Potassium Permanganate
(KMnO4).
3. Exposure to ultraviolet lamps emitting ozone.
4. Low temperature storage as in refrigeration and cold storage.
5. Controlled atmosphere (CA) or modified atmosphere (MA) shortage as in placing
commodities inside polyethylene bags.
6. Hypobaric storage.
7. Calcium infiltration for tomatoes, mangoes and avocados under vacuum.
8. Irradiation, waxing, dipping in kinetin or gibberellic acid have also been reported
to delay the ripening of certain fruits.
Self – evaluation:
1. Based on your observations, which treatment is best to use for hastening the ripening
of bananas? Why?
2. Why can leaves of some plants (madre de cacao), peelings of squash and ripe fruits
be used as ripening inducers?
3. How does calcium carbide induce the ripening of banana fruits?
4. Is it true that banana fruits ripened with calcium carbide have poor eating quality?
Explain.
5. Discuss the mechanism of ripening fruits.
Review of concepts:
As fruit-bearing plants grow, the fruits accumulate water and nutrients from the plant and
they use these nutrients to create their flesh and seeds. Most growing fruits initially provide
protection to the developing seeds. At this stage, fruits are generally hard and unattractive to
predators—including us! After seed development and fruit growth, the properties of the fruit
change to make the fruit more attractive to potential consumers, such as animals, birds, and
humans [1]. These changes include the most common ways by which we judge whether a
fruit is ripe or not, including external features, such as softness to the touch, and internal
features, such as sweetness. Fruits also change color as they ripen. This happens because
of the breakdown of a green pigment called chlorophyll, along with the creation and
accumulation of other pigments responsible for red, purple, or blue hues (anthocyanin), or
bright red, yellow, and orange hues (carotenoids), to name a few. (Moirangthem, K., & Tucker,
G. (2018).
Post Test:
Multiple Choices: Choose the correct answer.
1. The process by which certain fruit develops all its desirable characteristics.
a. Ripening b. maturity c. senescence d. ethylene
production
2. It is a hydrocarbon gas that triggers the ripening process in fruits.
a. C2H4 b. CO2 c. H2O2 d. MgCO3
3. As the fruit matures, it produces a small amount of ethylene until it reaches a critical
concentration that can stimulate more production of ethylene. What do you call to this
phenomenon?
a. autocatalytic production of ethylene c. natural production of
ethylene
b. auto catastrophic production of ethylene d. natural characteristic of
plants
4. The following are methods of slowing down ripening except one;
a. hypobaric storage
b. include ethylene and acetylene in the immediate environment of fruits.
c. exposure to ultraviolet lamps emitting ozone.
d. controlled atmosphere
5. What enzymes that turns acidic fruit to neutral one by converting them to neutral
molecules when the fruit ripens?
a. Amylase b. kinase c. hydrolase d. Pectinase
6. Another compound chemically related to ethylene which can act like ethylene to
ripening.
a. CaC2 b. C6H12O6 c. C2H4 d. KMnO4
8. What enzymes that turns fruit to become sweet when it ripens?
a. Amylase b. kinase c. hydrolase d. Pectinase
9. It is a ripening hormone that is produced from a fruit tissue.
a. exogenous ethylene b. acetylene c. endogenous ethylene d.
senescence hormone
10. A fruit that can be picked mature green and ripened after harvest.
a. Climacteric fruits b. non-climacteric c. juicy fruit d. jack fruit
References:
1. agritech.tnau.ac.in/Fruit Ripening
2. Moirangthem, K., & Tucker, G. (2018). How do fruits ripen. Front. Young Minds, 6, 1-7.
3. AusAID, DAT –BAT Factsheets in Postharvest Technology 1
