CHARACTERISTICS OF PREDOMINANT MICROORGANISM IN FOOD
Morphology and structure of microorganisms
a) Moulds
Eucaryotics cells*
Multicellular
Non motile, filamentous and branched
Compose of large numbers of filaments called hyphae which are
aggregated and called mycelium
Reproduction occurs from spore formation
e.g. penicllium spp
b) Yeasts
Eukaryotic cells*
Unicellular
Oval, spherical or elongated
Non motile, can see budding formation
Eg: Sacchromyces cerevisiae
Eukaryotic cells* - generally are:
Larger cells (20 to 100µm)
Cells have rigid cell walls and thin plasma membrane
Cytoplasm contains organelles such as mitochondria and vacuoles
c) Bacteria
Prokaryotic cells
Unicellular
Three morphology forms:
Spherical (cocci) – eg: streptococcus spp
Bacilli (rod) - eg: bacillus spp
Curved (coma) – eg:
Can be motile or non motile
The cytoplasmic materials are enclosed in a rigid wall on the
surface and a membrane beneath the wall
The organelle does not enclosed in a separate membrane
Bacterial are grouped as:
Gram negative = contain outer membrane which is compose of
lipo-polysaccharides (due to many enzymes,
antibiotics, salts, etc)
Gram positive = have thick wall composed of several layers of
mucopeptide and teicnoic acids
d) Viruses
Non cellular entities
Most important: bacteriophages (bacterial viruses)
Virus contain nucleic acid (DNA and RNA) and protein
FOOD SPOILAGE
1. INTRODUCTION
Food spoilage can be defined as any changes in the visual,
smell and texture of food that makes it unacceptable for
consumption.
Most serious economic problem in food processing industry.
Foods are subject to attack by microorganisms in a variety of
ways. Such attack is harmful to the quality of food.
Foods are organic substance and hence provide adequate
nutrients for the growth of wide varieties of microbes.
The physical and chemical characteristics of food and how it
is stored determine the susceptibility to microbial attack.
Spoilage may be due to one of the following:
a. Growth and activity of microorganisms.
b. Insects.
c. Action of enzymes to the plant and animal food.
d. Chemical reactions.
e. Physical changes (freezing, burning, drying,
pressure)
2. TYPE OF FOOD SPOILAGE
a. Physical spoilage
Dehydration of vegetable
b. Chemical spoilage
Oxidation of fat
Browning of fruits and vegetables
c. Microbial spoilage
Growth of microorganisms
Enzyme production
3. CRITERIA / PARAMETERS ASSOCITED WITH FOOD SPOILAGE
Odour
Texture
Shape
Formation of slime
Colour
Flavour
Gas production
4. SEQUENCE OF EVENTS IN FOOD SPOILAGE
Microorganisms have to get into the food
from a source or more
↓
Food environment should favour
the growth of microbes
↓
Food need to be stored under the growth
condition for a sufficient length of time:
To allow sufficient number necessary to cause
spoilage or changes in food.
To allow the produced enzyme to spoil the food.
5. HOW SPOILAGE OF FOOD IS DONE BY MICROORGANISMS?
These microorganisms use the food as their source of nutrients for
growth. By increasing their numbers, utilizing nutrients, producing
enzymatic changes and contributing off flavours by means of
breakdown of a product or synthesis of new compounds;
microorganisms can spoil the food.
6. WHY DOES YOUR FOOD CONTAIN MICROORGANISMS?
The interaction between microorganisms, plant and
animal are natural and constant. The food supply consists
basically of plants and animals and products derived from
them; it is understandable that our food can contain
microorganism in interaction with the food.
Food are derived from the soil (directly or indirectly)
which is the habitat for most microorganisms.
Microorganisms can also originated from exposure to air,
water or from natural microflora present in food as
commensals.
7. CLASSIFICATION OF FOOD
Perishability is a function of moisture content (Aw).
Stable food are those with low moisture content (low
Aw) whereas unstable foods have high water content(high
Aw)
To avoid any spoilage, food must be stored under
condition that microbial growth is slow or do not occur at all.
Foods can be classified into three groups based on ease of
spoilage:
I. Stable or non perishable foods.
Foods which do not spoil unless handle carelessly.
Example: Sugar, flour and dry beans.
II. Semi perishable foods.
If these foods are properly handled and stored, they will
remain unspoiled for a fairly long period. Examples:
potatoes, apples and nuts.
III.Perishable foods.
This group includes most of our important daily foods
that spoil readily unless special preservative methods are
used. Examples: meats, fish, milk, vegetables, eggs and
etc.
