FOOD SPOILAGE cPDST Home Economics CAUSES OF FOOD

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 • • • 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 30 minutes. • 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 • • 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.