3.2.1
Proteins & Carbohydrates
Changing Properties of Proteins
Changing Properties of Proteins
Here's an overview of the chemical and functional properties of proteins:
Denaturing
Denaturing
- 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
- 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
- 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
- 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
Changing Properties of Carbohydrates
Carbohydrates change in three main ways during cooking. Here's an overview of these changes:
Starch gelatinisation
Starch gelatinisation
- 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.)
- 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
- 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
- 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)
- 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.
1Food Preparation Skills
1.1Food Preparation Skills
1.1.1General Practical Skills
1.1.2Knife Skills
1.1.3Preparing Fruit, Vegetables & Using Equipment
1.1.4Cooking Methods: Prepare, Shape & Combine
1.1.5Sauce Making, Tenderising & Marinating
1.1.6Dough & Pastry
1.1.7Shaping & Finishing Dough
1.1.8Raising Agents & Mixtures
1.1.9End of Topic Test - Food Preparation Skills 1
2Food, Nutrition & Health
2.2Micronutrients
3Food Science
3.1Cooking of Food & Heat Transfer
3.2Functional & Chemical Properties of Food
4Food Safety
4.1Food Spoilage & Contamination
5Food Choice
5.1Factors Affecting Food Choice
5.2British & International Cuisines
6Food Provenance
6.1Environmental Impact & Sustainability of Food
6.1.1Food Sources - Intensive & Organic Farming
6.1.2Food Sources - Genetically Modified Crops
6.1.3Food Sources - Reared Food
6.1.4Food Sources - Caught Food
6.1.5Food & The Environment
6.1.6Food & The Environment 2
6.1.7Sustainability of Food
6.1.8Sustainability of Food 2
6.1.9End of Topic Test - Environmental Impacts
Jump to other topics
1Food Preparation Skills
1.1Food Preparation Skills
1.1.1General Practical Skills
1.1.2Knife Skills
1.1.3Preparing Fruit, Vegetables & Using Equipment
1.1.4Cooking Methods: Prepare, Shape & Combine
1.1.5Sauce Making, Tenderising & Marinating
1.1.6Dough & Pastry
1.1.7Shaping & Finishing Dough
1.1.8Raising Agents & Mixtures
1.1.9End of Topic Test - Food Preparation Skills 1
2Food, Nutrition & Health
2.2Micronutrients
3Food Science
3.1Cooking of Food & Heat Transfer
3.2Functional & Chemical Properties of Food
4Food Safety
4.1Food Spoilage & Contamination
5Food Choice
5.1Factors Affecting Food Choice
5.2British & International Cuisines
6Food Provenance
6.1Environmental Impact & Sustainability of Food
6.1.1Food Sources - Intensive & Organic Farming
6.1.2Food Sources - Genetically Modified Crops
6.1.3Food Sources - Reared Food
6.1.4Food Sources - Caught Food
6.1.5Food & The Environment
6.1.6Food & The Environment 2
6.1.7Sustainability of Food
6.1.8Sustainability of Food 2
6.1.9End of Topic Test - Environmental Impacts
Unlock your full potential with GoStudent tutoring
Affordable 1:1 tutoring from the comfort of your home
Tutors are matched to your specific learning needs
30+ school subjects covered