Explain the effects of cooking on the nutrients and sensory qualities of food, and describe ways to reduce nutrient loss

What this dot point is asking

SEAB wants you to explain how cooking changes food: both its nutrients and its sensory qualities (colour, texture, flavour and smell), and to describe how to cook so that the most nutrients are kept. The big idea is that cooking is a trade-off: it brings real benefits such as safety and better flavour, but some vitamins, especially vitamin C and the B group, are easily lost. The marks come from explaining the losses and from sensible ways to reduce them.

The answer

Good changes cooking makes

Cooking improves food in several ways beyond nutrients:

• Flavour and smell improve, for example the savoury taste of browned meat.
• Texture softens, making food more tender and easier to chew.
• Appearance and colour improve, making food more appetising.
• Starchy foods become easier to digest as the starch is broken down.
• Above all, cooking makes food safe by destroying harmful bacteria.

Why some nutrients are lost

The nutrients most affected by cooking are the water-soluble vitamins (vitamin C and the B group), for two reasons:

• Leaching: because they dissolve in water, they pass out of the food into the cooking water.
• Destruction by heat: vitamin C in particular is broken down by heat, and more is lost the longer and hotter the cooking.

The fat-soluble vitamins (A, D, E and K) and minerals are more stable, though some minerals can also leach into cooking water.

How cooking changes texture, colour and flavour

Heat changes food physically and chemically: starch swells and thickens sauces, protein sets (coagulates) as in a cooked egg, sugars brown (caramelise) to add colour and flavour, and vegetables soften as their structure breaks down. Overcooking can also make food dull in colour, mushy, or dry.

Reducing nutrient loss

To keep more nutrients, especially vitamin C:

• Steam rather than boil, so the food does not sit in water.
• Use only a little water and cook for a short time.
• Cut vegetables into larger pieces to reduce the surface area exposed to water and heat.
• Cook just until tender and serve soon, since vitamins are lost the longer food is kept hot.
• Use the cooking water in a soup or sauce so the dissolved vitamins are not wasted.

Examples in context

Example 1. Overboiled versus stir-fried vegetables. Vegetables boiled hard in a big pot of water for a long time turn dull and soft and lose much of their vitamin C into the water. The same vegetables given a quick stir-fry stay bright, crisp and far higher in vitamin C, showing how method and time decide how much goodness survives.

Example 2. Saving the goodness in a soup. When making a Chinese old cucumber soup or ABC soup, the vitamins and minerals that leach out of the vegetables stay in the broth. Because the soup itself is eaten, those dissolved nutrients are not wasted, showing how using the cooking liquid keeps nutrients that boiling would otherwise discard.

Try this

Q1. Explain why boiling vegetables for a long time in a lot of water reduces their vitamin C. [3 marks]

• Cue. Vitamin C is water-soluble so it leaches into the water, and it is destroyed by heat; more is lost the longer and the more water used.

Q2. Suggest three ways to cook vegetables that keep more vitamin C. [3 marks]

• Cue. Any three of: steam instead of boil, use little water and short cooking, cut into larger pieces, cook just until tender, use the cooking water in soup.

Q3. Describe two ways cooking improves food other than its nutrients. [2 marks]

• Cue. Any two of: better flavour and smell, softer texture, better appearance, easier digestion, and making food safe.