1. FOOD SPOILAGE
food once harvested, gathered (plants) or slaughtered (animals)
starts to deteriorate and leads to food spoilage!
there are 2 main factors:
1) natural decay within the food itself
2) contamination a) by microscopic forms of life
b) by other sources (chemicals etc)
food that spoil rapidly are perishable foods and contain
more amount of water, more amount of nutrients (milk, egg,
meat etc).
Processed and cooked food less susceptible, are foods with more
amount of salt, acid, sugar and less water.
1) Natural decay by A moisture loss
B action of enzymes
A: moisture loss: after harvesting (fruits and veg)
their metabolic reactions continue to respire so loss of moisture
through leaves and skin (before harvesting that loss was being
replaced through roots) vegetables and fruits shrink in size,
become limp and skin becomes wrinkled.
Also moisture loss occurs in meat – fish – cheese
evaporation from surface
B: action of enzymes: enzymes present in food and some
enzymes remain inactive until food is harvested or slaughtered
once activated enzymes speed up process of decay by
breaking down tissues in different ways:
- oxidation (destruction of B1, carotene, vit C (this occurs
without enzymes)
- browning: browning of apples
- ripening: banana passes from starch to sugar
2) Contamination by microorganisms
a) Microscopic plants or animals (many single cells)

2. (microorganisms) responsible for food contamination: A: bacteria
B: moulds
C: yeast
They all require: nutrients and moisture to grow and reproduce, so
food is an ideal place for them!! (because it has nutrients and
moisture)
They produce waste toxins (poison) contaminate food
sometimes, produce an illness: pathogenic microorganisms.
Not all are harmful, some are used in food industry ex: cheese,
yoghurt.
A: bacteria: classified according to their shape:
-Spherical shape (ex: staphylococci food poisoning)
- Rod shaped (ex: “clostridium botulidium” botulism)
- Spiral shape (ex: “vibrio cholera” cholera)
Conditions for bacteria to grow:PH 7, moisture or water present ,
temperature (10-40 ºC), oxygen and food supply.
Reproduction of bacteria: under the right conditions
reproduce very fast (% in 2 in 12 hours 16.000.000 bacteria!!!!)
B: moulds: tiny plants. Reproduce by spores that germinate
(bread, fruit, cheese).
Produce mycotoxins, harmful, we need to throw away all the food
C: yeast: single celled plant, found in air, soil and surface of
fruits naturally.
Very resistant!! food affected by them: fruit and fruit jam.
b) food contaminated by other sources:
radiation - pollution –chemicals like Weedkiller ,insecticide,
pesticide, fungicide.