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Green Shades in Food - Chlorophyll degradation
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Persistent green colour in our daily diet is an indication that necessary micronutrients and macronutrients are supplemented with the food. Green colour in vegetables is due to the presence of Chlorophyll pigments. This is the universal pigment that carries out photosynthesis in plants, algae and photosynthetic bacteria. Chlorophyll exists in two forms: "Chlorophyll A" and "Chlorophyll B".

Chlorophyll A (C55H72MgN4O5) is a complex molecule with a molecular weight of 893.49. It is a tetrapyrole structure consisting of phytol, a higher alcohol and a Mg2+ ion chelated in the centre. Chlorophyll A content is more in green food items. However, preservation of green colour is important in food industry. Persistence of natural green colour in food is an indication of a healthy food item to consumers.

If we consider the green colour in different food items such as dehydrated vegetables, green tea leaves, green chili sauce, porridge, olives, fermented products; there is a clear cut difference in the green shade. This results from various processing conditions used in cooking or preserving of the food. This green pigment which is naturally present is converted to various forms when exposed to different conditions. Concentration of Chlorophyll present, presence of phenolic compound which enhances enzymatic browning, entrapment of the pigment within cellulose, amount of acids present are also key factor for determining the specific shade of green apart from structural changes that occur in chlorophyll.

Chlorophyll is naturally present linked to a lipoprotein which protects it from acid digestion. These organic acids present in cell vacuoles are denatured during food processing. Phytol which is a higher alcohol in Chlorophyll makes the Chlorophyll molecule insoluble in water. It is observable when green leaves are put into water, water doesn’t become green. But when the leaves are macerated, it turns green. In maceration of green leaves when making porridge, green pigment and the Chlorophyllase enzyme present inside the cell comes out. Chlorophyllase enzyme removes the phytol group from the pigment producing Chlorophyllide A, which is water soluble. Chlorophyllide A is further degraded into purpurins in the presence of acids and Oxygen which results in loss of green colour. Chlorophyllide A is converted to Pheophorbide A in the presence of acids. Pheophorbide A is olive brown in colour. This also can be converted to Purpurins by oxidation.

Many food processing methods, involves heating the vegetables. The degree of heating differs when steaming, frying, tempering etc. This affects the green colour of the food. When heating green vegetables, pheophytinization can take place in which the Mg2+ ions are replaced by H+ ions producing pheophytin A from Chlorophyll A. Pheophytin A can be converted to purpurins and Pheophorbide under different conditions. In food processing, using high temperatures for a short time is effective in preserving green colour. Blanching is a good method to preserve green colour as it inactivates the enzyme system of the green vegetables. In drying, sun drying is not effective in retaining green colour. It enhances photochemical oxidation of Chlorophyll pigment.

Amount of phenolic compounds in vegetables indirectly affect the shade of green in food. These phenolic compounds are the substrate to enzymatic browning reactions. Product of enzymatic browning is a brown colour pigment known as melanin. This brown product masks the green colour that is naturally present. This occurs when the vegetables are cut, macerated, damaged which expose internal tissues to Oxygen.
Photochemical oxidation also results in change of natural green colour present in vegetables. This plays a significant role in selecting of packaging materials for marketing of green vegetables. Higher Oxygen concentration and light increase the rate of photochemical oxidation. Therefore, it’s a must to select packaging material with higher Oxygen and light barrier properties.

The labels on the food products may indicate that additives are not used. But the reality is, it is not possible to retain green colour without additives. Especially in acidic food products like sauce, natural pigments cannot be preserved without using preservatives.

However, in terms of health; Chlorophyll plays a vital role. Recent research focuses on the ability of Chlorophyll to retard cancer by reducing the damage to DNA caused by mycotoxins. It is also known to reduce stress, anemia, fatigue and speed up wound healing.
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