4.1.2

Enzymes & Signs of Food Spoilage

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High-Risk Foods

We classify ready-to-eat foods as high-risk foods if they can cultivate dangerous bacteria from being stored incorrectly.

High-risk foods

High-risk foods

  • Cooked fish, poultry and meat.
  • Gravies, sauces and stocks.
  • Shellfish.
  • Cooked rice.
  • Dairy products, such as cheese, milk and eggs.
Storing and classifying high-risk foods

Storing and classifying high-risk foods

  • These foods contain lots of protein and water.
  • Because there's a risk of bacteria multiplying rapidly, these foods cannot be kept safely for long (short shelf life).
  • We don't classify certain uncooked foods as high-risk foods because we don't consume them uncooked. Eggs are a good example.
Identifying 'off' food

Identifying 'off' food

  • Common signs that food is going off include:
    • Mould growing - on things like bread.
    • A sour smell - for things like yoghurt.
    • A slimy texture - for things like chicken.
  • But sometimes there are no signs that food has been spoiled, so we have to be careful.
Identifying spoil-free food

Identifying spoil-free food

  • Common signs include:
    • Fresh meat - smelling fresh, feeling firm and appearing bright.
    • Fresh fish - smelling clean or a little salty, with red-coloured gills, shiny skin and clear eyes.

Enzymes

Enzymes are biological catalysts that increase the rate of chemical reactions. They are proteins that cause fruits to either ripen or brown.

Ripening

Ripening

  • Fruits ripen because of the enzymes they contain.
  • Ripeness determines a fruit's colour, texture and sweetness.
  • Enzymes in bananas cause them to soften and sweeten by breaking down the starch they contain.
Browning

Browning

  • Slicing fruits and vegetables like pears and potatoes expose their insides to oxygen. The oxygen causes the fruit to brown and the enzymes in the fruit make this process happen faster.
  • Fruits also start to brown as they start to overripen.
Contolling enzyme activity

Contolling enzyme activity

  • Enzymes function best at an optimal pH. So, introducing an acid can stop enzymes from working properly.
    • E.g. pouring orange or lemon juice (acidic) over fruits will stop the fruits browning.
  • Enzymes ripen vegetables, causing them to gradually lose flavour, nutrients, colour and texture. Although freezing vegetables will slow enzyme activity, it won't end enzyme activity. Therefore, we must blanch foods to kill ripening enzymes and make sure vegetables are suitably colourful and nutritious for freezing.
Jump to other topics
1

Food Preparation Skills

1.1

Food Preparation Skills

1.1.1General Practical Skills1.1.2Knife Skills1.1.3Preparing Fruit, Vegetables & Using Equipment1.1.4Cooking Methods: Prepare, Shape & Combine1.1.5Sauce Making, Tenderising & Marinating1.1.6Dough & Pastry1.1.7Shaping & Finishing Dough1.1.8Raising Agents & Mixtures1.1.9End of Topic Test - Food Preparation Skills 1
2

Food, Nutrition & Health

2.1

Macronutrients

2.1.1Proteins2.1.2Proteins 22.1.3Fats2.1.4Carbohydrates2.1.5Carbohydrates 2
2.2

Micronutrients

2.2.1Fat-Soluble Vitamins2.2.2Water-Soluble Vitamins2.2.3Minerals & Water2.2.4Minerals & Water 22.2.5End of Topic Test - Macro & Micronutrients
2.3

Nutritional Needs & Health

2.3.1Informed Choices for a Balanced Diet2.3.2Informed Choices for a Balanced Diet 22.3.3Energy Needs2.3.4Nutritional Analysis2.3.5Diet Modifications2.3.6Diet-Related Problems2.3.7Diet-Related Problems 22.3.8End of Topic Test - Nutritional Needs & Health
3

Food Science

3.1

Cooking of Food & Heat Transfer

3.1.1Reasons for Cooking & Heat Transfer3.1.2Water-Based Cooking Methods3.1.3Fat-Based Cooking Methods3.1.4Dry Cooking Methods3.1.5Dry Cooking Methods 2
3.2

Functional & Chemical Properties of Food

3.2.1Proteins & Carbohydrates3.2.2Fats & Oils3.2.3Raising Agents3.2.4End of Topic Test - Food Science
4

Food Safety

4.1

Food Spoilage & Contamination

4.1.1Microorganisms & Signs of Food Spoilage4.1.2Enzymes & Signs of Food Spoilage4.1.3Food Poisoning4.1.4Bacterial Contamination4.1.5Microorganisms in Food Production
4.2

Principles of Food Safety

4.2.1Temperature Control4.2.2Ambient Foods & Food Labels4.2.3Preparing, Cooking & Serving Food4.2.4End of Topic Test - Food Safety
5

Food Choice

5.1

Factors Affecting Food Choice

5.1.1Factors Which Influence Food Choice5.1.2Food Choices5.1.3Religious Food Choices5.1.4Food Labels5.1.5Mandatory Food Labels5.1.6Optional Food Labels5.1.7Marketing Influences5.1.8End of Topic Test - Food Choice
5.2

British & International Cuisines

5.2.1British Cuisine5.2.2Japanese Cuisine5.2.3Japanese Ingredients & Dishes5.2.4Spanish Cuisine5.2.5Spanish Ingredients & Dishes
5.3

Sensory Evaluation

5.3.1Taste Receptors & Olfactory Systems5.3.2Sensory Testing Methods5.3.3Sensory Testing Methods 25.3.4End of Topic Test - Cuisines & Senses
6

Food Provenance

6.1

Environmental Impact & Sustainability of Food

6.1.1Food Sources - Intensive & Organic Farming6.1.2Food Sources - Genetically Modified Crops6.1.3Food Sources - Reared Food6.1.4Food Sources - Caught Food6.1.5Food & The Environment6.1.6Food & The Environment 26.1.7Sustainability of Food6.1.8Sustainability of Food 26.1.9End of Topic Test - Environmental Impacts
6.2

Food Processing & Production

6.2.1Primary Food Processing6.2.2Primary Food Processing 26.2.3Secondary Food Processing6.2.4Fortification6.2.5Additives6.2.6End of Topic Test - Food Processing & Production

Practice questions on Enzymes & Signs of Food Spoilage

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of the following are common signs that food is going off?True / false
  2. 2
    Which of the following are high-risk foods?True / false
  3. 3
    What colour will the gills of a fish be if it's spoil-free?Multiple choice
  4. 4
    Why does pouring lemon juice over fruits stop the fruits browning?Multiple choice
  5. 5
    Which of the following best describes enzymes?True / false
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Microorganisms & Signs of Food Spoilage

Food Poisoning