Experimental cookery

Potatoes must often contain flavones, as they sometimes develop a yellow or green color in alkaline water. Mashed potatoes that have a strong alkaline taste may be improved in flavor by adding a very small amount of cream of tartar. Flavones and flavonols with iron salts turn green and then brown. This 116 FRUITS AND VEGETABLES may explain some color changes that occur when foods are cooked in chipped enamel utensils having an iron base. Anthocyanins. The anthocyans include a group of pigments that, like sugars, have similar composition and properties yet have individual dif- ferences. As a rule they occur as glucosides in different parts of the plant and are known as anthocyanins in this combination. When the glucoside is hydrolyzed by boiling with dilute acid the non-glucosidal pigment portion is called anthocyanidin. The anthocyanins are soluble in water. Onslow states that occasionally they crystallize from the cell sap. Most but not all of the anthocyanins are soluble in alcohol. The anthocyan pigments give the blue, purple, violet, and red shades to different parts of the plant. They are very widely distributed. Onslow states that the plant that does not produce them is the exception rather than the rule. They occur in apples, cherries, currants, grapes, blueberries, red and black raspberries, in some varieties of peaches and plums, and in red cabbage, radishes, beets, and other fruits and vegetables. All the anthocyanins so far isolated have fallen into one of three groups. They are illustrated as the chlorides. The number of hydroxy groups attached to the side benzene ring is made the basis of the classification. The glucosides of these anthocyanidins are called pelargonins, cyanins, and delphinins. One of the reactions that the anthocyanins have in common is their color changes. Onslow states that the pigment should be pure to test the color reactions, for in the plant the pigment is found with other substances that may modify the reaction. In an acid solution, pure anthocyans are usually red ; in an alkaline one they are violet or blue, but if flavones or flavonols are present, a green color is obtained through the mixture of the blue and yellow. Yet the solutions of many fruit juices show typical color changes. In ordinary solutions of plant pigments they become green, then yellow, and sometimes brown upon the addition of alkali. If the alkali is very weak, or with salts with a weak alkaline reaction, a blue color may form and the green may never develop, or the blue may be intermediate between the red and the green.