Experimental cookery

Thompson reports that the total loss of solids, ash, and iron is greater in vegetables that are over-cooked than in those just sufHciently cooked. The Plant Acids The plant acids, the plant pigments, and the cellulose are constituents of the vegetable less often considered than the other food nutrients. Knowl- edge of the common reactions of these constituents renders one able to serve fruits and vegetables that are attractive in appearance, color, and texture ACIDS IN VEGETABLES 107 Plant acids. Plants contain organic acids. According to chemical classification the acids may belong to different groups, but for consideration in cooking they may be divided into two classes, the volatile and non- volatile ones. Volatile acids are the ones that volatilize and pass from the liquid as vapor. The odor of acetic acid or vinegar during cooking is vrell knovrn. The following acids of the CnHo„02 series are volatile, the first ones being more volatile than the last ones: Formic acid H-COOH Acetic acid CHg-COOH Propionic acid CH3-CH2'COOH Butyric acid CH3 • CH2 • CH2 • COOH Valeric acid CH3 • CH2 • CH2 • CH2 • COOH Caproic acid CH3 • CH2 • CH2 • CH2 • CH2 • COOH Formic and acetic acids have been obtained from plants during distilla- tion. Onslow states that propionic acid has only rarely been found in plants. The amount of volatile acids found in plants varies ; it also varies in the same plant. Koch found that cooking 125 grams of spinach for 1 hour and collecting the distillate required 18 cc. of N/\0 NaOH to neutralize the volatile acids. Another experiment in which the same weight of spinach was used and cooked for the same length of time required only 6 cc. of N/\0 NaOH. Non-volatile acids. Not all the acids found in fruits and vegetables are volatile. The following are some of the more common non-volatile ones found in foods: Dicarboxylic acids OxaHc acid COOH • COOH Malonic acid COOH • CH2 • COOH Succinic acid COOH • CH2 • CH2 • COOH Glutaric acid COOH • (CH2)3 • COOH Adipic acid COOH • (CH2)4 • COOH Hydroxydicarhoxylic acids MaHc acid COOH • CHOH • CH2 • COOH Tartaric acid COOH ■ CHOH • CHOH • COOH Hydroxytricarboxylic acids Citric acid COOH • CH2 • COH • CH2 • COOH I COOH Acids in vegetables. The acids are found in the fruits, leaves, stem, and root stocks. The acid may occur in the free form, but is often com- bined as a salt or an ester. Because of oxaluria the oxalic acid content of vegetables is of interest. Onslow states that oxalic acid ''occurs very frequently and widely dis- 108 FRUITS AND VEGETABLES