What are the functional and chemical properties of food, and why do ingredients behave the way they do when cooked?
Functional and chemical properties of carbohydrates, proteins and fats: gelatinisation, dextrinisation, caramelisation, protein coagulation and denaturation, the Maillard reaction, foam formation, shortening, aeration, plasticity and emulsification.
A focused answer to the WJEC Food Preparation and Nutrition science of food topic on functional and chemical properties, covering the behaviour of carbohydrates, proteins and fats including gelatinisation, caramelisation, coagulation, denaturation, the Maillard reaction, aeration, shortening and emulsification.
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What this dot point is asking
You need to know the functional and chemical properties of carbohydrates, proteins and fats: how each behaves when prepared and cooked, with the correct terms, so you can explain why recipes work and why faults happen.
Properties of carbohydrates
- Gelatinisation
- Starch heated in liquid absorbs it, swells and bursts at about 80 to 90 degrees Celsius, thickening the mixture (sauces, custards).
- Dextrinisation
- Starch cooked with dry heat browns and changes flavour on the surface (toast, bread crust).
- Caramelisation
- Sugar heated above about 160 degrees Celsius melts and browns, developing a caramel colour and flavour (toffee, caramel).
Properties of proteins
- Coagulation: egg sets a quiche; meat and fish firm up when cooked.
- Denaturation: whisking egg white, or adding lemon juice to fish (which firms it), unravels the protein.
- Foam formation: whisking egg traps air to make a foam (meringue, whisked sponge).
- The Maillard reaction: at high temperatures, protein and sugar react to brown food and develop savoury flavour (the crust of roast meat and baked bread).
Properties of fats
- Shortening: fat coats flour, stops gluten forming, gives a short, crumbly texture (shortcrust pastry).
- Aeration: creaming fat with sugar traps air, helping cakes rise.
- Plasticity: fats soften over a range of temperatures, so they spread and rub in.
- Emulsification: an emulsifier (such as the lecithin in egg yolk) holds oil and water together so they do not separate (mayonnaise).
Emulsions
Examples include mayonnaise (oil in vinegar, held by egg yolk), salad dressings, and milk and cream (natural emulsions of fat in water). Without an emulsifier, the oil and water would quickly separate into layers.
Why these properties matter in the exam
WJEC often gives you a dish and asks which properties are at work, or asks you to explain a fault: a lumpy sauce (starch not gelatinised smoothly), a flat sponge (not enough air trapped, or the protein did not set), tough pastry (gluten developed instead of shortening), or split mayonnaise (the emulsion broke). Knowing the property and its cause lets you both explain and fix the problem.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style6 marksExplain the functional and chemical properties shown by the ingredients when making a white sauce thickened with flour, and a whisked sponge.Show worked answer →
A 6-mark question. Mark it for correct properties linked to each product.
In a white sauce, the starch in the flour gelatinises: when heated in the milk, the starch grains absorb liquid, swell and burst at about 80 to 90 degrees Celsius, thickening the sauce. The fat in the roux also helps coat the starch so it does not lump. In a whisked sponge, the egg shows aeration and foam formation: whisking traps air in the egg to make a foam, and the sugar helps stabilise it; when baked, the egg protein coagulates (sets) around the trapped air, holding the risen structure, while the starch in the flour also sets.
A top answer names gelatinisation for the sauce and aeration plus coagulation for the sponge, explaining each. Reward precise terms and the temperatures or stages.
WJEC style3 marksExplain what is meant by an emulsion and how an emulsifier helps, using mayonnaise as an example.Show worked answer →
A 3-mark question on emulsification.
An emulsion is a mixture of two liquids that do not normally mix, such as oil and water (or vinegar), with one spread as tiny droplets through the other. Normally they separate, but an emulsifier holds them together: in mayonnaise, the lecithin in egg yolk acts as an emulsifier, coating the oil droplets and keeping them spread evenly through the watery vinegar so the mixture stays smooth and thick and does not separate.
Markers reward: an emulsion is two liquids that do not mix, one in droplets in the other; an emulsifier keeps them mixed; and egg yolk (lecithin) does this in mayonnaise.
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Sources & how we know this
- WJEC Eduqas GCSE Food Preparation and Nutrition specification (from 2016) — WJEC Eduqas (2016)