Experimental cookery

Reactions of chlorophyll with alkalies. Chlorophyll is a neutral substance but gives characteristic reactions when treated with alkalies or acids. Will- statter designates the parent substance of chlorophyll as chlorophyllin. The reaction of chlorophyllin with methyl and phytol alcohols gives the ester chlorophyll. Chlorophyll, when treated in the cold with alkalies, gives alkaline salts of chlorophyllin. The color change is first brown, followed by a return of the green, but it is no longer fluorescent. When chlorophyll is saponified with hot alcoholic alkalies, isochlorophyllins are formed, which are fluorescent. COOCH3 C32H3oON4Mg/ + 2 MOH COOC20H39 chlorophyll a alkali COOM C32H3oON4Mg/ COOM + CH3OH + C20H39C alkali salt of chlorophyllin methyl alcohol phytol alcohol When the green-colored vegetables are cooked in water with an alkaline reaction, or in water to which a small amount of soda is added, they develop a bright, intense green color. Reaction of chlorophyll with acids. Chlorophyll reacts with acids to give an olive-colored product, without fluorescence, called phaeophytin. The magnesium of the chlorophyll is replaced by hydrogen. From phaeophytin, Willstatter has obtained two decomposition groups: the first, designated as phytochlorins, are olive green and derived from chlorophyll a; the second, the phytorhodins, are red and derived from chlorophyll b. COOCH3 C32H3oON4Mg/ + 2Hx > COOC2oH39 chlorophyll a acid (C32H320N4)(COOCH3)(COOC2oH,9) -f MgX2 phaeophytin magnesium salt The effect of heat upon chlorophyll. The chlorophyll is changed to the olive-green color by two means, ( 1 ) by hydrogen ions or an acid reaction and (2) by heat. As previously given, the hydroxyl ions, or an alkaline reac- tion, produces chlorophyll salts with bright green color. In general, the more acid the reaction, the more rapid is this change in color w^hen the vegetable is heated ; or, vice versa, the more alkaline the reaction, the more slowly the chlorophyll changes to olive-green. Thus in order that the bright green color be retained in cooking green vegetables, they should be cooked CHLOROPHYLL 113 for as short a time as possible and contact with acids should be avoided as far as possible. It is also possible that other ions than the hydrogen and hydroxyl ions may affect the stability of the chlorophyll, for some vege- tables with nearly the same />H, cooked in water from the same source, and with other conditions standardized are more stable to heat than others. In cooking certain procedures may aid in decreasing the acidity of the cooking water. The vegetables contain both volatile and non-volatile acids, which in the plant are prevented from uniting with the chlorophyll but are liberated when the plant tissues are heated. If the cooking vessel is not covered, the volatile acids may escape with the steam, thus decreasing the acidity. It has been found that the highest percentage of these volatile acids passes off during the first few minutes of cooking. Hence, if the cooking vessel needs to be covered for a part of the time, it is preferable to have the uncovered period the first few minutes.