can penetrate rapidly to all parts of the leaf, cooking it very quickly, so they do not generally
undergo colour loss. Leafy vegetables should actually be cooked in small amounts of water to
prevent the unnecessary leaching of nutrients.
5. Larger vegetables should be cut into smaller portions which cook faster, thus reducing cooking
time and therefore colour loss. (However this will increase vitamin loss)
III/IV - 8 (of 11)
· Cooling on ice :
Cooling green vegetables on ice does NOT “preserve” the green colour of chlorophyll any more than if
they were cooled normally. However, it does affect the texture – it “stops the cooking process”,
preventing the beans from cooking further after having removed them from the cooking water. Also,
further nutrient losses occur in cooling in ice, so it is more sensible to remove the beans from the
cooking water just before they have reached the desired texture, because they will continue to cook
slightly as they are left to cool alone.
Except for beetroot whose pigments are particular and called betalains, most red to blue plant tissue
(red cabbage, purple peppers, purple potatoes, radishes, and eggplant skins)owe their colour to
pigments that are called anthocyanins. An example of the molecular structure of these pigments is
Anthocyanins does not have a problem of acid replacement like the chlorophyll so unlike the green
vegetables, these vegetables should be cooked in as little water as is necessary, to prevent too much
nutrient loss, or too much looss of colour (the anthocyanins are very soluble in water).
Like most pigments, the form and therefore colour of the anthocyanins is highly affected by pH.
Anthocyanins can exist in different forms depending on pH. In acidic conditions, the anthocyanins
adopt a form which reflects red light, keeping the cabbage a nice red colour. In alkaline conditions
however, one of the important alight absorbing groups is changed, and the overall form of the pigment
is changed so that now it is the blue light that is reflects. Tap water, which may be used for cooking,