Wednesday, April 12, 2017

Green pigments in green vegetables

Green vegetables contain the green pigment chlorophyll which plays a key role in transferring light energy to chemical energy during growth and development of the plant by the prices of photosynthesis. Examples of such green vegetables include spinach, peas, beans, cabbage lettuce and celery.

Although chlorophyll does not appear to be useful in human physiology, foods that are high in chlorophyl are usually also high in B-carotene.
There are two types of chlorophyll and each produces a specific colour in green plants. Chlorophyll A is blue-green, whereas the more common chlorophyl B is green. Their chemical compounds differ in colour because of their different structures - chlorophyl a has a methyl group (-CH2) attached to one of the carbons on the chlorophyl molecule, whereas chlorophyl B has an aldehyde group (-CHO). Destruction of chlorophyl increases with cooking time.

Chlorophyll A is more readily converted to pheophytin than chlorophyll B. Green vegetables should be cooked for a very short time, less than minuets to retain the colour. Vegetables like peas, beans, greens are sometimes canned.

During canning chlorophyl gets converted to pheophytin due to the high temperatures used. Sometimes for stain the colour and to neutralise the acid, alkali is added.
Green pigments in green vegetables
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