food contanmination sudy material 1 .pdf

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1. Food Contamination

2. •To know the three methods of food
contamination.
•To understand the two different food changes
through autolysis and micro-organisms.
•To identify positive food changes.
•To know the conditions which promote
bacterial growth.
Learning objectives

3. •Food contamination refers to the presence of
harmful chemicals and microorganisms in
food which can cause consumer illness.
•A food contaminant has been defined as any
substance not intentionally added to food,
which is present in such food as a result of the
production, manufacture, processing,
preparation, treatment, packing, transport or
storage.

4. •It is important to protect food from risk of
contamination to prevent food poisoning and
the entry of foreign objects.
•There are three main ways in which food can
become contaminated:
(i) Microbial Contamination;
(ii) Physical Contamination;
(iii) Chemical Contamination.

5. •Definition: Food spoilage can be defined
•as a disagreeable change in a food's normal
state.
•NOT acceptable for human consumption and
for food industrial usage
•Such changes can be detected by smell, taste,
touch, or sight.
•Food safety « food quality

6. •Classifications of food spoilage
•Stable or non perishable foods (sugar, flour,
dry beans)
•Semi perishable foods :Foods handled and
stored properly → remain unspoiled for long
period (potatoes, apples)
•Perishable foods: Spoil readily without special
preservative methods (fish, meat, eggs, milk)

7. •Main causes of food spoilage
•Physical changes: aw, temperature, mechanical effects
•Caused by the inappropriate transport, handling and
storage
•Biological factors:
•Microbiological: bacteria, yeasts, molds (most common)
•Macrobiological: 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)

8. PHYSICAL CONTAMINATION
•One of the major concerns in producing
meat animals.
•Handling
•Treating
•Feeding
•Transporting

9. PHYSICAL PROBLEMS
❑Bruising
❑Injection site problems
❑Stress
❑Contamination

10. This can also occur in a variety of ways at different
stages of food processing and production.
Some examples are:
• soil from the ground when harvesting;
• a bolt from a processing plant when packaging;
• a hair from a cook in the kitchen.
Care must be taken at each stage to prevent
physical contamination.

12. Chemical contamination
This can occur in a variety of ways at different
stages of food processing and production.
Some examples are:
• chemicals from the farm;
• a cleaning product used in the processing
plant when packaging;
• fly spray used in the kitchen when preparing
food

13. Chemical Contaminants
•Intentional Food Additives
–Use of materials which enhance the
acceptability of the products and/or aid in the
development of the product
•Unintentional Food Additives

14. Residues
This includes both food processing component
residues as well as PESTICIDES, ANTIBIOTIC OR
HORMONE IMPLANT residues
Natural Toxicants
Product Tampering
Nutritional Components

15. Microbial Contamination
•If food is consumed that has been
contaminated by certain, harmful bacteria
(pathogenic bacteria) or their toxins (poisons
produced by some of these bacteria), food
poisoning may result.

16. •Bacteria are responsible for most food
poisoning cases.
•Symptoms of food poisoning may include
vomiting, diarrhoea, fever and abdominal
pain.
•The symptoms may take some time to occur
depending on the type of bacteria (incubation
period).

17. •As soon as food is harvested, slaughtered or
manufactured into a product it starts to
change. This is caused by two main processes:
• autolysis – self destruction, caused by
enzymes present in the food;
• microbial spoilage – caused by the growth of
bacteria, yeasts and moulds.

18. Desirable food changes
Autolysis and micro bacterial changes are sometimes desirable
(and are not referred to as spoilage), for example enzymes cause
fruit to ripen.
Here are some positive micro bacterial
changes below.
Bacteria in yoghurt
production.
Mould in some
cheeses, e.g. Stilton.
Yeast in bread
production.

19. Autolysis - enzymes
Enzymes are chemicals that are found in food.
These chemicals have important uses in food. They can cause
food to deteriorate in three main ways:
• ripening – this will continue until the food becomes inedible,
e.g. banana ripening;
• browning – enzymes can react with air causing the skin of
certain foods, e.g. potatoes and apples discolouring;
• oxidation – loss of certain nutrients, such as vitamins A, C and
thiamine from food, e.g. over boiling of green vegetables.

20. Microbial spoilage - bacteria
These are single celled micro-organisms (they cannot
be seen by the naked eye) which are present naturally
in the environment.
There are many different kinds, some are useful, e.g. in
the production of yogurt, and some harmful.
The presence of bacteria in food can lead to digestive
upset.
Some bacteria produce toxins which can lead to this
also.
Spores can also be produced by some bacteria leading
to toxins being produced.

21. Microbial spoilage - yeast
Yeasts are single celled fungi which can reproduce
by ‘budding’. This means that a small offshoot or
bud separates from the parent yeast cell. Yeasts
can also form spores which can travel through the
air. These are easily killed by heating to 100ºC.
In warm, moist conditions in the presence of sugar,
yeasts will cause foods like fruit to ferment
producing alcohol and carbon dioxide gas.
Yeast is used in the production of bread and wine.

22. Microbial spoilage - mould
Moulds are fungi which grow as filaments in food.
They reproduce by producing spores in fruiting bodies
which can be seen on the surface of foods.
These fruiting bodies sometimes look like round furry
blue-coloured growths, e.g. mould on bread.
Some moulds can be seen by the naked eye, e.g. on
bread.

23. Conditions for bacterial growth
Micro-organisms need conditions to survive and
reproduce these can include:
• temperature;
• moisture;
• food;
• time;
• oxygen;
• pH level.

24. Conditions for bacterial growth
Temperature
Bacteria need warm conditions to grown and multiply.
The ideal temperature for bacterial growth is
30ºC – 37ºC.
Some bacteria can still grow at 10ºC and 60ºC. Most bacteria are
destroyed at temperatures above 63 ºC. Bacterial growth danger
zone in 5ºC - 63ºC.
At very cold temperatures, bacteria become dormant – they do
not die, but they cannot grow or multiply.

25. Conditions for bacterial growth
100ºC Water boils
82ºC Core temperature of hot food
5ºC - 63ºC danger zone for
rapid growth of micro-organisms
1ºC - 4ºC temperature of fridge
0ºC Freezing point of water
-18ºC temperature of freezer

26. Conditions for bacterial growth
Moisture
Where there is no moisture bacteria cannot grow. However,
bacteria and moulds can both produce spores which can survive
until water is added to the food.
Food
Bacteria need a source of food to grow and multiple, these food
usually contain large amounts of water and nutrients.
Time
One bacterium can divide into two every 20 minutes. Food where
bacteria rapidly multiple in are called perishable foods.

27. Conditions for bacterial growth
Oxygen
Some bacteria need oxygen to grow and multiply.
These are called aerobic bacteria. Other bacteria
grow well when there is no oxygen present, these are
known as anaerobic bacteria.
pH level
An acidic or alkaline environment can promote of
inhibit microbial growth. Most bacteria prefer a neutral
pH (6.6 – 7.5). Moulds and yeasts can survive at pH
levels of 1-1/5 (very acidic), food spoilage usually
occurs by yeast and moulds.

28. Food poisoning /food- intoxication due to microbes is very
common; some of the foods borne diseases are given below-

29. •Consequences/effects of food spoilage
• changes in nutritional value
• Decomposition of proteins, carbohydrates,
vitamins
•changes in organoleptic features
•colour, flavour, taste, consistency…. mucilaginous
surface, unpleasant odour,
•unwholesome effects: Biogenic amines, toxins,
•Metabolites of microorganisms
•Pathogen microbes

30. •Controls :
•• Prevent cross-contamination:
•Cross-contamination occurs when bacteria are
transferred onto food either directly (e.g.
when raw and cooked food come into direct
contact, sneezing or coughing onto food) or
indirectly (e.g. via a vehicle such as from dirty
utensils, pests, hands etc.)

31. •Prepared and cooked foods should be stored
separate to raw foods and unprepared
vegetables to reduce the risk of cross-
contamination.
•Keep stored foods covered.
• Prevent animals and insects entering the food
room.

32. • Keep food preparation areas and utensils
clean.
• Wash hands frequently,
•• Keep cuts, boils etc., covered with a
waterproof dressing (preferably coloured).
• • Do not handle food if suffering from
symptoms of diarrhoea or vomiting and notify
your supervisor immediately.

33. •To multiply, bacteria require food, warmth,
moisture and time.
•By removing one or more of these criteria the
growth of bacteria can be slowed or even
stopped.

34. •store foods at safe temperatures (either cold
below 8°C or hot above 63°C);
•cook food thoroughly;
•do not prepare food too far in advance;
•avoid keeping food at room temperature for
any longer than necessary
•prevent dry foods becoming moist.

35. •Food can also be contaminated with fungus
which includes:
•Mycotoxin: Toxic substances produced by moulds or
fungi are called as Mycotoxin.
•some mycotoxins are mutagenic and carcinogenic in
nature.
•of these mycotoxins , Aflatoxin is of most common
occurrence in the agricultural produce/ food.
• Aflatoxins are produced by a fungus – Aspergillus
flavus and Aspergillus parasiticus.