Food Science

Question 1

Why Food Is Cooked

Answer 1

Food is cooked for several reasons, including:

✔ Making food safe to eat – Cooking kills bacteria and harmful pathogens (e.g., salmonella in poultry).

✔ Making food more digestible/palatable – Heat breaks down tough fibres in meat and vegetables, making them easier to chew and digest.

✔ Enhancing flavour, aroma, texture, and appearance – Cooking caramelises sugars, crisps surfaces, and enhances colours.

✔ Preservation – Some cooking methods, such as pasteurisation, extend shelf life.

Question 2

Heat Transfer in Cooking

Answer 2

Food is cooked through three heat transfer methods:

✔ Conduction – Heat is transferred directly through contact (e.g., frying in a pan, grilling).

✔ Convection – Heat moves through air or liquid (e.g., boiling, baking, roasting).

✔ Radiation – Heat is transferred as waves (e.g., grilling, microwaving).

Question 3

How Preparation and Cooking Affect Nutritional Value

Answer 3

✔ Enrichment/loss – Some cooking methods can increase or reduce nutrient content.
• Boiling vegetables leads to vitamin C loss.
• Steaming retains more vitamins than boiling.
• Cooking tomatoes increases lycopene (an antioxidant).

✔ Increase/reduce calorific value –
• Frying adds calories due to added fat.
• Grilling or steaming keeps calorie content lower.

Question 4

How Cooking Methods Affect Food Properties

Answer 4

✔ Texture – Cooking softens or crisps food (e.g., roasting makes potatoes crispy).

✔ Flavour – Caramelisation and Maillard reaction enhance taste (e.g., browning of toast).

✔ Appearance – Cooking changes colour and shape (e.g., eggs turn white when cooked).

✔ Aroma – Heating releases volatile aroma compounds, making food smell better.

Question 5

Working Characteristics and Functional & Chemical Properties of Ingredients

Answer 5

1. Carbohydrates

✔ Gelatinisation – When starch absorbs liquid and swells when heated, thickening sauces (e.g., roux sauce, custard).

✔ Dextrinisation – When starch is heated, it turns brown and crisp (e.g., toast, baked bread).

✔ Caramelisation – When sugar is heated, it turns golden brown and develops a richer flavour (e.g., caramel, crème brûlée).

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2. Fats and Oils

✔ Shortening – Fats coat flour particles in pastry, preventing gluten formation and making the texture crumbly (e.g., shortcrust pastry).

✔ Aeration – Beating fat with sugar traps air, making mixtures light and fluffy (e.g., creamed cake mixtures).

✔ Plasticity – The ability of fats to be spreadable at different temperatures (e.g., butter vs. margarine).

✔ Emulsification – Fats and water don’t mix unless an emulsifier (e.g., egg yolk) is used (e.g., mayonnaise).

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3. Proteins

✔ Coagulation – When proteins set when heated, changing texture (e.g., frying eggs, setting custard).

✔ Foam formation – Proteins trap air when whisked, making foams (e.g., meringues).

✔ Gluten formation – When flour and water mix, gluten develops, making dough stretchy and elastic (e.g., bread dough).

✔ Denaturation – Proteins change shape when exposed to heat, acid, or mechanical action (e.g., cooking meat, marinating fish in lemon juice).

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4. Fruit and Vegetables

✔ Enzymic browning – When fruit is cut, oxygen reacts with enzymes, turning it brown (e.g., apples, bananas).
• Prevented by lemon juice (acid) or refrigeration.

✔ Oxidisation – Some vitamins (especially vitamin C) are lost when food is exposed to air and heat.

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5. Raising Agents

✔ Yeast – A biological raising agent that produces carbon dioxide gas (e.g., bread).

✔ Chemical raising agents – Bicarbonate of soda and baking powder produce gas bubbles when heated (e.g., cakes, scones).

✔ Air and steam – Whisking and beating trap air, and steam expands in baked goods (e.g., choux pastry, Yorkshire puddings).