Experimental cookery

The tin salts have not been found poisonous, but large amounts of them in a food, such as would result when an acid fruit is cooked for a long time in a tin wash boiler, produce a very dark color and a disagreeable metallic flavor. Iron salts with acids may cause discoloration in some food products. Plant Pigments Chlorophyll. Chlorophyll, the green pigment of plants, plays an im- portant role in their synthesis of carbohydrates. The cells of the mesophyll of the leaf contain chloroplasts or chlorophyll-corpuscles, the nucleus, other substances, and the cell liquid with its dissolved materials. The chloro- plasts contain four pigments, two green ones, chlorophyll a and chlorophyll Z>, and two yellow ones, carotene and xanthophyll. Solubility of chlorophyll. Chlorophyll is not soluble in water. Very little CHLOROPHYLL 111 green color is found in the water in which green vegetables have been cooked. Pure isolated chlorophyll is soluble in acetone, ether and benzene. In extracting the pigment from thoroughly dry leaves it is necessary to add about 20 per cent of water to the acetone or other solvent. One explana- tion for this is that chlorophyll is in the colloidal state in the leaf, and the mineral constituents of the leaf, dissolved in the water, peptize it, rendering it soluble. Onslow states that "the condition of chlorophyll is altered by plunging into boiling water. The pigment is then much more soluble, in ether, etc., even when the leaves are subsequently dried. It is supposed that the chlorophyll has diffused out from the plastids, and is in true solution in the accompanying waxy substances which have become liquid owing to change in temperature." When green vegetables are dropped into boiling water a change takes place nearly instantly, the green color being intensified. Various explana- tions have been offered for the phenomenon. One is that the hot water has melted waxy constituents of the leaf so the chlorophyll escapes from the cell more readily or may become more soluble. Or the hot water may have dissolved salts or other substances in contact with the chlorophyll so that it diffuses more readily. For peas, Kohman states that one factor in the intensification of the green color is the removal of air from the pea when it is dropped in the boiling water. The outer skin of the pea is transparent, the space beneath this being impregnated with air which is removed when the peas are blanched. That this change in color is caused by removal of the air can be shown by subjecting the peas to an adequate vacuum under cold water and releasing the vacuum while the peas are still under the water. Composition of chlorophyll. Willstatter, whose work gave us the formula for and the chemical reactions of chlorophyll, reports that it exists in two forms, depending upon the degree of oxidation in the plant cells: form {a) and form {b) . The former exists in the proportion of three to one of the latter. COOCH3 COOH C32H3oON4Mg<^ C32H,cON4Mg<^ COOC20H39 COOH chlorophyll a chlorophyllin COOCH3 C32H2802N4Mg/ COOC20H39 • chlorophyll b Chlorophyll contains 2.7 per cent of the metal magnesium. It contains two ester groups, one of methyl alcohol (COOCH3) and one of phytol alcohol (COOC20H39). 112 FRUITS AND VEGETABLES