the vegetable will lose water as if it is “wilting”. Care needs to be taken that the vegetables are not
overcooked – or they will become overly soft and undesirably mushy. Vegetables are sometimes
salted while cooking, to bring out their taste as the salt diffuses into them. However, the salt draws the
liquid out of the vegetables by osmosis, and this further softens the vegetables.
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Vegetables contain many nutrients and are an important source of vitamins in our diet – especially
vitamins A, B and C. Many of the nutrients are destroyed when the vegetable is cooked, either by
dissolving into the cooking water, or by being broken down or destroyed by the heat. Although vitamin
A and the molecules that form it are not water soluble, both vitamin B and C as well as the minerals
are, and will leak into the cooking liquid. Finely chopped vegetables are especially prone to losses of
vitamin C. Finely cut up vegetables expose a large surface area to the cooking water for vitamin C
loss, but additionally, because the vegetables have been finely chopped, sufficient amounts of an
enzyme that further contributes to the degradation of vitamin C. This enzyme is most active at high
temperatures, although it is degraded in boiling water, and so has a most pronounced effect as soon
as the vegetables to be boiled are added to the boiling water, since the water temperature temporarily
drops to below boiling.
The other nutrients that are most commonly lost include sugars and starch.
Nutrient losses increase with cooking time and volume of cooking liquid.
Prevention of the leaking of nutrients can therefore be helped by cooking vegetables in a small
amount of water, or else using the cooking water to make a sauce/soup etc
Changes to colour
Green vegetables are green because their cells contain large amounts of the pigments chlorophylls,
which are a large molecules containing a magnesium ion at its centre.
Green vegetables also contain other coloured pigments but in much smaller quantities.