Source: https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-2-enzymes-and-signs-of-food-spoilage [Revision notes](https://senecalearning.com/en-gb/revision-notes.md) › [GCSE](https://senecalearning.com/en-gb/revision-notes/gcse.md) › [Food Preparation](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation.md) › [AQA](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa.md) › Enzymes & Signs of Food Spoilage # Enzymes & Signs of Food Spoilage Food Preparation & Nutrition: AQA GCSE, topic 4.1.2 ## 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](https://image-v2.cdn.app.senecalearning.com/2018-05/f825fd48-1b1e-4f63-83b6-5f3240cec317/shutterstock_435521527.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-05/64f00306-272e-481f-972e-4c2d2e9730c0/egg-3413544_1920.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2020-03/a239fbd0-99b4-4252-aa3f-8cfb37d1fb93/mouldy-bread-.jpeg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-05/97dc117f-f83a-4312-933a-9a363e83499a/shutterstock_475848682.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-05/21fd4d6b-eed2-4c02-9127-8af681d05325/shutterstock_252318739.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-05/5db09848-45ed-48d5-86a2-b25ca75c4cab/shutterstock_333836696.jpg) - 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. ### Controlling enzyme activity ![Controlling enzyme activity](https://image-v2.cdn.app.senecalearning.com/2018-05/1c82b5a4-4d82-41d5-ab1f-4515c0dc6d13/shutterstock_211542739.jpg) - 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. ## Test yourself on Enzymes & Signs of Food Spoilage - Which of the following are common signs that food is going off? - Which of the following are high-risk foods? - What colour will the gills of a fish be if it's spoil-free? - Why does pouring lemon juice over fruits stop the fruits browning? - Which of the following best describes enzymes? [Practise this topic for free](https://app.senecalearning.com/classroom/course/d59d0e60-4fa8-11e8-bbba-738ab127bed6/section/ba06d3fb-0eec-4296-9bda-c5d0ed217328/session) - Previous topic: [4.1.1 Microorganisms & Signs of Food Spoilage](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-1-microorganisms-and-signs-of-food-spoilage.md) - Next topic: [4.1.3 Food Poisoning](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-3-food-poisoning.md) ## Food Preparation & Nutrition: AQA GCSE contents ### 1 Food Preparation Skills - 1.1 Food Preparation Skills - [1.1.1 General Practical Skills](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-1-general-practical-skills.md) - [1.1.2 Knife Skills](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-2-knife-skills.md) - [1.1.3 Preparing Fruit, Vegetables & Using Equipment](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-3-preparing-fruit-vegetables-and-using-equipment.md) - [1.1.4 Cooking Methods: Prepare, Shape & Combine](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-4-cooking-methods-prepare-shape-and-combine.md) - [1.1.5 Sauce Making, Tenderising & Marinating](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-5-sauce-making-tenderising-and-marinating.md) - [1.1.6 Dough & Pastry](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-6-dough-and-pastry.md) - [1.1.7 Shaping & Finishing Dough](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-7-shaping-and-finishing-dough.md) - [1.1.8 Raising Agents & Mixtures](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-8-raising-agents-and-mixtures.md) - [1.1.9 End of Topic Test - Food Preparation Skills 1](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/1-1-9-end-of-topic-test-food-preparation-skills-1.md) ### 2 Food, Nutrition & Health - 2.1 Macronutrients - [2.1.1 Proteins](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-1-1-proteins.md) - [2.1.2 Proteins 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-1-2-proteins-2.md) - [2.1.3 Fats](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-1-3-fats.md) - [2.1.4 Carbohydrates](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-1-4-carbohydrates.md) - [2.1.5 Carbohydrates 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-1-5-carbohydrates-2.md) - 2.2 Micronutrients - [2.2.1 Fat-Soluble Vitamins](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-2-1-fat-soluble-vitamins.md) - [2.2.2 Water-Soluble Vitamins](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-2-2-water-soluble-vitamins.md) - [2.2.3 Minerals & Water](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-2-3-minerals-and-water.md) - [2.2.4 Minerals & Water 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-2-4-minerals-and-water-2.md) - [2.2.5 End of Topic Test - Macro & Micronutrients](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-2-5-end-of-topic-test-macro-and-micronutrients.md) - 2.3 Nutritional Needs & Health - [2.3.1 Informed Choices for a Balanced Diet](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-1-informed-choices-for-a-balanced-diet.md) - [2.3.2 Informed Choices for a Balanced Diet 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-2-informed-choices-for-a-balanced-diet-2.md) - [2.3.3 Energy Needs](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-3-energy-needs.md) - [2.3.4 Nutritional Analysis](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-4-nutritional-analysis.md) - [2.3.5 Diet Modifications](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-5-diet-modifications.md) - [2.3.6 Diet-Related Problems](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-6-diet-related-problems.md) - [2.3.7 Diet-Related Problems 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-7-diet-related-problems-2.md) - [2.3.8 End of Topic Test - Nutritional Needs & Health](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/2-3-8-end-of-topic-test-nutritional-needs-and-health.md) ### 3 Food Science - 3.1 Cooking of Food & Heat Transfer - [3.1.1 Reasons for Cooking & Heat Transfer](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-1-1-reasons-for-cooking-and-heat-transfer.md) - [3.1.2 Water-Based Cooking Methods](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-1-2-water-based-cooking-methods.md) - [3.1.3 Fat-Based Cooking Methods](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-1-3-fat-based-cooking-methods.md) - [3.1.4 Dry Cooking Methods](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-1-4-dry-cooking-methods.md) - [3.1.5 Dry Cooking Methods 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-1-5-dry-cooking-methods-2.md) - 3.2 Functional & Chemical Properties of Food - [3.2.1 Proteins & Carbohydrates](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-1-proteins-and-carbohydrates.md) - [3.2.2 Fats & Oils](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-2-fats-and-oils.md) - [3.2.3 Raising Agents](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-3-raising-agents.md) - [3.2.4 End of Topic Test - Food Science](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-4-end-of-topic-test-food-science.md) ### 4 Food Safety - 4.1 Food Spoilage & Contamination - [4.1.1 Microorganisms & Signs of Food Spoilage](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-1-microorganisms-and-signs-of-food-spoilage.md) - [4.1.2 Enzymes & Signs of Food Spoilage](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-2-enzymes-and-signs-of-food-spoilage.md) - [4.1.3 Food Poisoning](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-3-food-poisoning.md) - [4.1.4 Bacterial Contamination](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-4-bacterial-contamination.md) - [4.1.5 Microorganisms in Food Production](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-1-5-microorganisms-in-food-production.md) - 4.2 Principles of Food Safety - [4.2.1 Temperature Control](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-2-1-temperature-control.md) - [4.2.2 Ambient Foods & Food Labels](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-2-2-ambient-foods-and-food-labels.md) - [4.2.3 Preparing, Cooking & Serving Food](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-2-3-preparing-cooking-and-serving-food.md) - [4.2.4 End of Topic Test - Food Safety](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/4-2-4-end-of-topic-test-food-safety.md) ### 5 Food Choice - 5.1 Factors Affecting Food Choice - [5.1.1 Factors Which Influence Food Choice](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-1-factors-which-influence-food-choice.md) - [5.1.2 Food Choices](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-2-food-choices.md) - [5.1.3 Religious Food Choices](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-3-religious-food-choices.md) - [5.1.4 Food Labels](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-4-food-labels.md) - [5.1.5 Mandatory Food Labels](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-5-mandatory-food-labels.md) - [5.1.6 Optional Food Labels](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-6-optional-food-labels.md) - [5.1.7 Marketing Influences](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-7-marketing-influences.md) - [5.1.8 End of Topic Test - Food Choice](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-1-8-end-of-topic-test-food-choice.md) - 5.2 British & International Cuisines - [5.2.1 British Cuisine](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-2-1-british-cuisine.md) - [5.2.2 Japanese Cuisine](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-2-2-japanese-cuisine.md) - [5.2.3 Japanese Ingredients & Dishes](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-2-3-japanese-ingredients-and-dishes.md) - [5.2.4 Spanish Cuisine](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-2-4-spanish-cuisine.md) - [5.2.5 Spanish Ingredients & Dishes](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-2-5-spanish-ingredients-and-dishes.md) - 5.3 Sensory Evaluation - [5.3.1 Taste Receptors & Olfactory Systems](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-3-1-taste-receptors-and-olfactory-systems.md) - [5.3.2 Sensory Testing Methods](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-3-2-sensory-testing-methods.md) - [5.3.3 Sensory Testing Methods 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-3-3-sensory-testing-methods-2.md) - [5.3.4 End of Topic Test - Cuisines & Senses](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/5-3-4-end-of-topic-test-cuisines-and-senses.md) ### 6 Food Provenance - 6.1 Environmental Impact & Sustainability of Food - [6.1.1 Food Sources - Intensive & Organic Farming](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-1-food-sources-intensive-and-organic-farming.md) - [6.1.2 Food Sources - Genetically Modified Crops](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-2-food-sources-genetically-modified-crops.md) - [6.1.3 Food Sources - Reared Food](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-3-food-sources-reared-food.md) - [6.1.4 Food Sources - Caught Food](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-4-food-sources-caught-food.md) - [6.1.5 Food & The Environment](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-5-food-and-the-environment.md) - [6.1.6 Food & The Environment 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-6-food-and-the-environment-2.md) - [6.1.7 Sustainability of Food](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-7-sustainability-of-food.md) - [6.1.8 Sustainability of Food 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-8-sustainability-of-food-2.md) - [6.1.9 End of Topic Test - Environmental Impacts](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-1-9-end-of-topic-test-environmental-impacts.md) - 6.2 Food Processing & Production - [6.2.1 Primary Food Processing](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-1-primary-food-processing.md) - [6.2.2 Primary Food Processing 2](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-2-primary-food-processing-2.md) - [6.2.3 Secondary Food Processing](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-3-secondary-food-processing.md) - [6.2.4 Fortification](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-4-fortification.md) - [6.2.5 Additives](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-5-additives.md) - [6.2.6 End of Topic Test - Food Processing & Production](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/6-2-6-end-of-topic-test-food-processing-and-production.md)