Experimental cookery

If red cabbage is served raw with a salad dressing containing acid it is bright red or blue-red in color. If cooked in distilled water, it is violet or violet-blue in color, but often becomes blue after standing a few min- utes. With a slightly alkaline water the color is blue, for the plant acids lower the />H of the water. If the water is distinctly alkaline the color becomes green if cooked about 15 minutes or longer. The addition of a little soda to distilled water, Experiment 17B, 5, gives a green color unless the cooking period is exceptionally short. The red vegetables tend to retain 120 FRUITS AND VEGETABLES their color better when cooked in milk than when cooked In water. Red onions show the same color changes as red cabbage, but the colors are often muddy. Red cabbage shows color changes in handling it. When the cut edges of the cabbage come in contact with the hands or knife they turn blue. Hands and knives washed in hard water or with soap may have salts with an alkaline reaction on their surface, but the anthocyanins can also form compounds with metallic ions. Beets do not develop the blue or green color, although the color often contains a considerable amount of blue or purple. Sometimes they turn from red to yellow when cooked. If the cooked beets are placed in acid, the red color is often restored after a short time. Blair states that beets contain two pigments, one being scarlet the other purple. The scarlet pigment is stable to heat, but the purple one fades. The scarlet pigment is stable even in the alkaline range as far as pH 9 or, according to Pratt and Swartout, even at pH 13.0. The color of canned or cooked beets depends upon the proportion of the two pigments present in the beets. This is probably an explanation of why cooked beets vary so much in color, even when cooked under the same conditions of acidity, temperature, and time. Beets have been produced in which the scarlet pigment has been increased and which do not lose color when canned at high temperatures. Metals and anthocyan pigments. The tin salts of the anthocyanins have been mentioned, but the iron salts are even better known. In general, the iron salts of anthocyanins are blue. It is known that juice from blue hydrangeas contains a higher percentage of iron than that from pink hydrangeas even at the same pH. Some anthocyanins may not combine with iron or other modifications may occur which prevent or are necessary for the development of the blue color, for if some anthocyanins are treated with iron salts the color fades or remains red. Other metals which may combine with the anthocyanins are aluminum, zinc, and lead. Aluminum produces about the same colors as iron, although less intense. It seems reasonable to expect that, if certain salts are present in the vegetable in high concentration or are furnished by the cooking water or the cooking utensil, they will modify colors obtained at a given pH in cooking. Also, the blue color that develops on the cut surface of red cabbage in a short time after cutting with a metal knife may possibly be due to formation of anthocyanin salts with the metal.