Ochg

COO-phytyl

Chlorophyll a

Chlorophyll b

Figure 1. Formulas for chlorophylls a and b and the phytol moiety.

Phytol

Phytol

Figure 2. Numbering system for the chlorophylls.

alfalfa (lucerne), Medicago sativa; nettles, Urtica dioica; and a series of pasture grasses such as fescue. In a living cell, within the chloroplasts, the chlorophylls are com-plexed with but not covalently bound to one of a series of polypeptides. The chlorophyll-polypeptide or chlorophyllprotein complexes are closely associated with carotenoids and tocopherols (vitamin E) and are actively involved in the processes of photosynthesis. Preparation of a colorant involves recovery and purification of an appropriate form of chlorophyll.

Land plants are usually available for only a few weeks of the year; thus, the chlorophyll colorants are usually made from bulk harvested and dried plants. The dried plants are ground and extracted with acetone or a chlorinated hydrocarbon solvent and washed, and the solvent is removed. A yield of 20% of a mixture of chlorophylls, pheo-

phytins, and other degraded chlorophyll compounds is usually obtained. The dry residue after removal of the solvent can be further purified by treatment with a water-immiscible solvent to obtain an oil-soluble preparation known as metal-free pheophytin. The dry residue can also be acidified in the presence of copper salts to produce an oil-soluble copper pheophytin. It is not commercially practical to produce a colorant containing chlorophyll itself because of the instability of the magnesium compound. The dry residue can also be saponified to replace the phytyl group with sodium or potassium to form water-soluble compounds. After further purification, the product may be marketed as a water-soluble, metal-free, gray-green product. Acidification in the presence of copper salts converts the pigments to more-stable green pigments known as copper chlorophyllins.

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