Food spoilage occurs when microorganisms like bacteria, yeasts, and molds degrade the nutritional value, texture, and flavor of food, making it unsuitable for consumption. The main causes of food spoilage are physical changes in conditions like temperature and biological factors such as microbial growth. Spoilage can lead to changes in a food's nutritional content, appearance, and production of toxins. Various signs like odor, sliminess, and discoloration indicate microbial spoilage. Proper food preservation techniques aim to inhibit microbial growth or kill microorganisms to prevent spoilage and potential food poisoning.

2. FOOD SPOILAGE

3.  Food spoilage means the original nutritional val
ue, texture, flavor of the food are damaged, the
food become harmful to people and unsuitable
to eat.

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5. • Food spoilage can be the result of:
– Insect damage
– physical injury
– Enzymatic degradation
– Microbial activity
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6. Main causes of food spoilage
Physical changes
• aw, temperature, mechanical effects
• Caused by the inappropriate transport, handling and storage
Biological factors
• Microbiological
• Bacteria, yeasts, moulds (most common)
Microbiological
• Rodents, insects, birds, parasites
• Chemical, biochemical factors
• Non-microbial or enzymatic changes usually involving
oxygen ® oxidation processes (e.g., rancidity of fats and oils)
• Activity of endogenous tissue enzymes (food of vegetable or
animal origin)
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7. Effects of food spoilage
Changes in nutritional value
• Decomposition of proteins , carbohydrates,
vitamins
Changes in organoleptic features
• Colour , flavour , taste, unpleasant odour.
Unwholesome effects
• Biogenic amines, toxins,
• Metabolites of microorganisms
• Pathogen microbes
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8. Spoilage Signs
• Odor:
– Breakdown of proteins (putrefaction)
e.g. “rotten egg” smell
• Sliminess
- Primarily due to surface accumulation of microbial cells
and also be a manifestation of tissue degradation
• Discoloration
– Mould on bread, blue and green mould on citrus fruit
and cheese
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9. • Souring
– Production of acid
e.g. sour milk from production of lactic
acid
• Gas formation
– Meat becomes spongy
– Swollen or bubbling packages and cans
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11. Two types of Spoilage:
• Microbial spoilage
• Non- Microbial
Based on rate of spoilage:
• Highly perishable
– Meat, fish, poultry, eggs, milk, most fruits
and vegetables.
• Semi perishable
– Potatoes, some apple varieties, nutmeats
• Stable or non-perishable
– Sugar, flour, dry beans 11

12. a. Physical spoilage
• moisture loss or gain
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13. b. Chemical spoilage
• Oxidation of fat
• Browning of fruits and vegetables
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14. c. Microbial spoilage
• Growth of microorganisms
• Enzyme production
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15. Microbial spoilage of food
• Bacteria, yeasts and moulds are the major causes of food
spoilage.
• They produce various enzymes that decompose the various
constituents of food.
• Moulds are the major causes of spoilage of foods with
reduced water activity.
e.g dry cereals and cereal product
• Bacteria spoil foods with relatively high water activity such
as milk and products.
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16. Sources of microorganisms in food
The primary sources of microorganisms in food
include:
1. Soil and water
2. Plant and plant products
3. Food utensils
4. Intestinal tract of man and animals
5. Food handlers
6. Animal hides and skins
7. Air and dust
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17. Factors affecting microbial growth
(a) Intrinsic factors:
These are inherent in the food. They includ
e:
• Hydrogen ion concentration (pH),
• Moisture content,
• Nutrient content of the food,
• Antimicrobial substances ad
• Biological structures.
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18. (b). Extrinsic factors
• Are factors external to the food that affect
microbial growth. They include:
1. Temperature of storage,
2. Presence and concentration of gases in
the environment
3. Relative humidity of food storage
environment.
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19. Microbial spoilage – how does it manifest
itself?
• Visible growth
• Gas production
• Slime
• Off-flavours
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21. Sequence of events in food spoilage
Microorganisms have to get into the food from a source
↓
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.
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22. SPOILAGE OF CEREALS
• Moisture content above 12 to 13 percent may cause
spoilage of cereals
• Little moisture cause mould growth and high moisture
may cause growth of yeasts and bacteria.
• Microbial content, physical damage and temperature
are also some factors.
• Aspergillus, Penicillium, Mucor, Rhizopus, Fusarium are
some common moulds; produce mycotoxins.
• Acetobacter spp, lactics and Coliforms, Micrococci and
Bacillus are some species causing spoilage.

24. SPOILAGE OF MILK
• An excellent medium
• Souring
– caused by Streptococcus lactis, Enterococci.
• Gas production
– caused by Coliform, Clostridium, Yeasts.
• Proteolysis
– cause bitter taste, caused by Bacillus ,
Micrococcus.
• Changes in colour and tastes
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26. SPOILAGE OF MEAT
• Raw meat is subject to spoilage by its own
enzymes and microbial action.
• Excessive autolysis can cause souring
• Factors involving spoilage include
– The greater gut load of animal
– The physiological condition of the animal during
slaughter as like fever, excited or fatigued.
– Rapid cooling
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28. SPOILAGE OF FISH
• Spoiled by autolysis, oxidation or bacterial
activity.
• Under aerobic conditions Change in colour
of meat pigments
• Red colour, green , brown or grey.
• Off odours and Off tastes
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30. SPOILAGE OF EGGS
• Cracks, leaks, stained or dirty spots on exterior
and blood clots, bloodiness, translucent spots
in the interior are all signs of spoilage
• Pseudomonas, certain coliform bacteria. Proteus spp,
Aeromonas, Serratia, Sporotrichum all cause rots in eggs.
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32. SPOILAGE OF CANNED FOODS
• Chemical spoilage
– Hydrogen swell
– Discolouration of inside of the can
– Cloudiness of liquors
– Loss in nutritive value
• Biological spoilage
– Attacked by
• Thermophilic and
• Mesophilic bacteria
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34. Vegetables
• Vegetables are a good substrate for yeasts, moulds or
bacteria
• It is estimated that 20% of all harvested fruits and
vegetables for humans are lost to spoilage by these
microorganisms.
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35. Soft rot
a. One of the most common types of bacterial spoilage.
b. caused by Erwinia carotovora
• Softening can also be caused by endogenous enzymes
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36. Mould spoilage
a. In vegetables where bacterial growth is not favored ,
moulds are the principal spoilage agents.
b. Most moulds must invade plant tissue through a
surface wound such as a bruise or crack.
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37. Fruits
• Like vegetables, fruits are nutrient rich substrates but the pH
of fruits does not favor bacterial growth. As a result, yeasts
and moulds are more important than bacteria in the
spoilage of fruits.
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39. Fermented products
Beer
• Spoilage in packaged beer is often due to
growth of the yeast Saccharomyces
diastaticus, which grows on dextrins that
brewers yeast cannot utilize.
• In either case, spoilage by yeasts results in
the development of turbidity, off flavors and
odors.
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41. Wines
• Candida valida is the most important spoilage yeast in
wine
This reduces the acidity of the wine and adversely
affect wine flavor.
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42. SPOILAGE CAN LEAD TO…
Food Poisoning
• When someone gets sick from eating food or
drink that has gone bad or is contaminated.
• There are two kinds of food poisoning:
poisoning by toxic agent or by communicable
agent.
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43. FOOD PRESERVATION
• Food preservation is the process of treating and
handling food ,with an aim to stop or slow down its
spoilage while maintaining its nutritional value, texture,
and flavour.
• Food preservation methods either kill microbes or
prevent their growth.
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44. Food preservation principles
• Two general principles are employed in food
preservation.
(1). Inhibition principle
(2). Killing principle
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45. (1). Inhibition principle
• In this principle, food preservation is achieved by
inhibition of growth and multiplication of
microorganisms.
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46. (2). Killing principle
• In this principle, spoilage microorganisms are
destroyed (Killed) in the food, and the food
protected against subsequent contamination
by being enclosed in an air tight container.
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47. Some methods are:
1. Boiling
2. Dehydration
3. Refrigeration & freezing
4. Canning
5. Using chemical preservatives
6. Using Salt, sugar, oil, or vinegar
7. Pasteurization
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48. How to reduce food spoilage
• Remove expired or spoiled food
• Store food in the right parts of your
refrigerator
• Prevent mould growth in the refrigerator
• Keep some foods separate to prevent
spoilage
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