FOOD SPOILAGE

WHY DOES FOOD ‘GO OFF’?

Causes of food spoilage:1. Moisture loss2. 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

RipeningEnzymes 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. Toxic2. 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

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.

(H) FOOD POISONING BACTERIA

Learn 3 common strains of food poisoning bacteria: e.g.

Salmonella, Staphylococcus aureus, Listeria monocytogenes.

Habitat /SourcesFactors affecting growthHigh risk foodsIncubation periodToxic or infectiousSymptoms