tends to be slightly on the alkaline side, which will cause a natural red-blue colour change during
Therefore to retain the desired red colour, these anthocyanin containing vegetables, for example red
cabbage, should be cooked in the presence of a small amount of acid. Indeed cooked red cabbage
often contains red wine vinegar, or is served with sour cream.
Cook red cabbage in a little water. Then add acid to taste and cook further
watching the unappetizing blue-purple color shift rapidly to red.
Flavone is one the pigments present in white vegetables (like cauliflower). The flavones are soluble in
water and oil so vegetables containing these pigments should only be cooked for short amounts of
time. Like the other pigments the wavelengths of lights that the pigments absorbs and reflects is
affected by pH. The pigment stays white in an acid medium and turns yellow in an alkaline medium.
Therefore, to prevent this undesirable colour change, a small amount of lemon juice, cream of tartar,
or vinegar should be added to the cooking liquid when cooking white vegetables to create a slightly
acidic medium, favourising the desired white colour.
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Yellow and orange vegetables:
Carotenoids are the pigments found in yellow and orange vegetables, like carrots and tomatoes.
Carotenoids are only slightly affected by acids or alkalis.
Vegetables containing carotenoids can be cooked for a relatively long time without significant colour
loss because like the other pigments described above, the carotenoids are soluble in fat but insoluble
in water, so the colour of these vegetables are hardly changed by boiling in water – carrots stay
orange and tomatoes stay red.
However, pressure cooking can deform the carotenoid molecules, and changes their structure, and will
alter their colour from reddish-orange to yellow-orange.
The cooking paradox
In general, vegetables should be cooked at high temperatures. High temperatures ensure increased
volatility of volatile compounds, so an improved taste; and ensures the desirable texture changes that