Transcript Food Spoilage

FOOD SPOILAGE
(c)PDST Home Economics
CAUSES OF FOOD SPOILAGE
• 1. Moisture loss
• 2. Enzyme action
• 3. Microbial contamination
1. SPOILAGE BY MOISTURE
LOSS
• Mainly affects fruit and vegetables.
• After harvesting they can no longer get water from the
soil.
• Moisture is lost through skins and leaves.
• Causes wrinkling, shrinkage and limpness.
2. ENZYME ACTION
• Ripening
Enzymes cause food to ripen, then become over-ripe and
eventually decay. Starch changes to sugar, colour
changes and texture softens.
• Browning
When certain foods are cut and the surface exposed to
air, enzymes cause them to turn brown. e.g. apples,
• Enzymatic rotting
Enzymes in fish cause deterioration even at low
temperatures.
CONTROLLING ENZYMATIC
SPOILAGE
• Inactivated by heating - cooking, canning.
• Cold temp slows action - cool storage.
• Enzymes in vegetables work at low temperatures so
they must be blanched before freezing.
• Acid inactivates enzymes - lemon juice used to stop
browning.
• Sulphur dioxide stops enzymatic spoilage.
3. MICROBIAL
CONTAMINATION
• Yeast, mould and bacteria are the microbes that
cause food spoilage.
• Food at the optimum temperature is the ideal place
for microbes to grow.
• Yeast and mould spoil the outside of food and can be
seen.
• If the food is eaten it will probably be harmless,
unless they make mycotoxins.
• Bacteria cause spoilage by making toxins in food - not
visible.
• Souring bacteria spoil milk, yoghurt & cream.
FOOD POISONING
3 types
• 1.Chemical –Caused by pesticides, antibiotics, metals.
• 2.Biological – Caused by toxins naturally present in
food e.g. red kidney beans, green potatoes.
• 3.Bacterial - Caused by pathogenic bacteria in food
SYMPTOMS
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Abdominal cramps
Nausea
Vomiting
Diarrhoea
Fever
Loss of appetite
Don’t eat for 24 hours. Drink cooled boiled water.
BACTERIAL FOOD
POISONING
2 types
• 1. Toxic
• 2. Infectious
(H) 1. TOXIC BACTERIAL FOOD
POISONING
• Caused by eating food containing toxins.
• Exotoxins are made by bacteria in the food before
and after it’s eaten.
• Exotoxins are difficult to destroy - must be boiled
for 30minutes.
• Symptoms develop quickly - within a few hours of
eating the food.
• Exotoxins are made by Staphylococci, Clostridium
botulinum.
(H) 2. INFECTIOUS BACTERIAL
FOOD POISONING
• Caused by eating food containing large numbers of
pathogenic bacteria that produce endotoxins.
• The endotoxins are released when the bacteria die in your
intestine.
• Endotoxins are easily destroyed by normal
cooking/heating of food.
• Symptoms take longer to occur - over 12 hours.
• Salmonella and listeria cause infectious food poisoning.
(H) HIGH RISK FOODS
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Liquid protein foods.
Milk, cream, eggs.
Meat, poultry, fish.
Meat dishes e.g. pies, gravies.
Soups and stocks.
Egg dishes e.g. custard, mayonnaise.
Reheated dishes.