Source: https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-1-proteins-and-carbohydrates

[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) › Proteins & Carbohydrates

# Proteins & Carbohydrates

Food Preparation & Nutrition: AQA GCSE, topic 3.2.1

## Changing Properties of Proteins

Here's an overview of the chemical and functional properties of proteins:

### Denaturing

![Denaturing](https://image-v2.cdn.app.senecalearning.com/2018-05/7a43b3ca-cf76-4612-95a6-28b1f371cc7a/shutterstock_700551553.jpg)

- Chemical bonds hold proteins' complex structures together. These break down during cooking, causing proteins to denature. 
- Proteins fall apart and change shape. This is often an irreversible transformation.
- Things that cause proteins to be denatured include:
 - Temperature changes.
 - Acidic substances (e.g. fruits like kiwifruit, mango, pineapple and fig are good at breaking down meat proteins).
 - Agitation (beating or whisking).

### Coagulation

![Coagulation](https://image-v2.cdn.app.senecalearning.com/2018-05/4cb4e053-2bc4-433c-af4f-02436be8b7d5/shutterstock_449570035.jpg)

- When denatured, protein molecules bang into other protein molecules and join together (coagulate). When this happens, water gets stuck between the protein molecules.
- Coagulation alters food texture and how it looks - e.g. egg white transforms from a clear liquid into a white solid. 
- Coagulation can help things stick together - e.g. when eggs are mixed with breadcrumbs.
- Too much coagulation can be problematic. The food becomes dry and chewy as the protein tightens and water is pushed out of the molecules.

### Foams

![Foams](https://image-v2.cdn.app.senecalearning.com/2018-05/fd767fcf-90c9-432f-a532-a77c9cbccf3d/shutterstock_678365650.jpg)

- Chocolate mousse and meringues are examples of foams. We make them by trapping gas inside liquids.
- When we agitate liquids storing protein (e.g. by whisking or beating), we cause the liquids' proteins to denature. The denatured proteins expand, trapping air in the liquid.
- Then, when coagulation happens the air gets trapped and a foam is formed.
- Over-beating or over-whisking will break coagulation bonds, causing the air to escape and the foam to fall apart.
- When some foams are cooked, they become solid (e.g. egg white foams → meringues).

### Role of gluten

![Role of gluten](https://image-v2.cdn.app.senecalearning.com/2018-05/c13386fe-11f1-4b52-bbd9-79a9f2f0af01/shutterstock_657290233.jpg)

- Gluten is a form of protein. Wheat flours contain gluten. 
- We get gluten by mixing water and flour to form dough. 
- Gluten molecules can bend and stretch - we say they are coiled. This is why dough is stretchy.
- We knead dough to lengthen, strengthen and stretch the gluten strands - this is called 'working' the gluten.
- Gluten coagulates at high temperatures, while dough remains stretched. As a result, foods, such as well-risen bread, gain an airy texture.

## Changing Properties of Carbohydrates

Carbohydrates change in three main ways during cooking. Here's an overview of these changes:

### Starch gelatinisation

![Starch gelatinisation](https://image-v2.cdn.app.senecalearning.com/2018-05/1e0d2f53-ecbe-4fb8-bda5-13600be5ce83/shutterstock_673562746.jpg)

- Starch gelatinisation thickens starchy foods, like pasta sauces and gravy.
- Starch granules hang in liquid until they're heated. The intermolecular bonds begin to break and water is absorbed. This causes the starch granules to soften and expand (swell).
- The starch granules start to burst once temperatures reach 62°C-80°C. Starch is released into the liquid. 
- The liquid is thickened by the addition of starch. The more starch that is released, the thicker the liquid becomes.

### Starch gelatinisation (cont.)

![Starch gelatinisation (cont.)](https://image-v2.cdn.app.senecalearning.com/2018-09/a53e7128-5efa-434c-b4f6-f55d135f5efa/pasta-carbohydrate-food.jpg)

- Cooling the liquid turns it into a solid gel, which can be used for desserts which require set fillings (like key lime pie). 
- Gelatinisation occurs when cooking spaghetti and other forms of pasta - the strands expand, become soft and starch is released into the liquid.

### Dextrinisation

![Dextrinisation](https://image-v2.cdn.app.senecalearning.com/2018-05/d6905ec3-6357-4abf-aecc-ed7f19c68677/shutterstock_332807894.jpg)

- Dextrinisation describes the process of starch molecules breaking down into dextrins (smaller molecules) when starchy foods are exposed to dry heat. 
- The process causes food to brown, develop a crispier texture and taste different.
 - Cooking time affects how dark and crispy the food turns. The longer the cooking time, the browner and crispier the food becomes.

### Caramelisation

![Caramelisation](https://image-v2.cdn.app.senecalearning.com/2018-05/b866d9f9-7ba3-4301-a6a0-1c1cf914664b/shutterstock_751182496.jpg)

- Caramelisation occurs when sugar molecules are exposed to high heat - they break down, the sugar browns and its flavour changes.
- There are different stages of caramelisation:
 - Initially, the liquid is sweet-tasting and runny.
 - The liquid thickens with time and develops a caramel-like texture.
 - The liquid eventually hardens and develops a candy-like texture as it cools.

### Caramelisation (continued)

![Caramelisation (continued)](https://image-v2.cdn.app.senecalearning.com/2020-03/cff4d873-57bd-4a34-b142-b953b158ec3b/creme-brulee-.jpg)

- It's often necessary to add water at the start of the heating process to avoid burning the caramelised sugar. Once caramelised sugar starts to burn, it turns brittle and black.
- Caramelisation adds sweetness. 
- Some desserts are therefore caramelised (e.g. creme brulee) as well as some savoury foods, like shallots.

## Test yourself on Proteins & Carbohydrates

- What causes proteins to denature?
- Formation of Foams
- What process happens when sugar molecules are exposed to high heat?
- The Stages of Caramelisation
- Which of the following is true of caramelisation?

[Practise this topic for free](https://app.senecalearning.com/classroom/course/d59d0e60-4fa8-11e8-bbba-738ab127bed6/section/5cd4e240-5855-11e8-9078-fb33f179496c/session)

- Previous topic: [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)
- Next topic: [3.2.2 Fats & Oils](https://senecalearning.com/en-gb/revision-notes/gcse/food-preparation/aqa/3-2-2-fats-and-oils.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)