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

Vitamins as antioxidants in processed foods

Vitamins as antioxidants in processed foods
Oxidation, a series of chemical reactions yielding undesirable and products (off odors, colors, and flavors), may occur in many fruits and vegetables and foods high in fat and oil during exposure to air, light, heat, heavy metals, certain pigments or alkaline conditions. Enzymatic browning may occur in some fruits and vegetables, particularly apples, banana, peaches, pear, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, the phenolases catalyze oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.

Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids (building blocks of fats and oils) to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.

The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are susceptible to oxidation, unsaturated fatty acids are significantly more susceptible than their saturated counterparts at room temperatures and at elevated temperatures.

Antioxidants, as defined by Food and Drug Administration are “substances used to preserve food by retarding deterioration, rancidity or discoloration due to oxidation.” Some oxidations have more than one function. For example, Ascorbic acids may function as a free-radical chain terminator, and oxygen scavenger, or a metal chelator. Under certain conditions, it may act as a promoter for oxidation.
Vitamins as antioxidants in processed foods