Experimental cookery

Cruess, Mark, and Quinn state that the oxidase of peaches is not all destroyed by blanching at 120° to 160°F., thus causing internal browning with the formation of crescent shaped areas often seen in sliced peaches. To destroy the action of the oxidase of large peach halves requires heating for 10 minutes at 180° to 200°F. These investigators state that fruit acids such as citric and tartaric are not so effective as hydrochloric acid in retarding browning. Oxidation was completely held in check by 0.25 per cent of hydrochloric acid, so that this concentration on the surface of the peach would prevent browning. Salt and other chlorides will check brown- ing temporarily; but, after standing in a 2-per cent salt brine, the fruit must be rinsed to remove the flavor of salt. Prevention of browning by reducing substances. Joslyn and Marsh state that the primary oxidation step may be prevented by removal of oxygen or the addition of reducing substances. And without oxidation browning does not occur. Sulfites and stannous salts are good reducing substances. Sulfur dioxide has been used for many years to prevent dis- coloration. They state that orange juice does not brown at high or low temperatures when stored in tin cans. The reason given is absence of oxygen and the reducing action of stannous salts. The addition of ferrous salts in concentrations of 25 parts per million to the orange juice increased browning. Ferrous salts were more effective than ferric salts. Nickel, copper, or stannic salts were without effect, but stannous salts and sulfites protected against browning. However, after these salts were oxidized, 126 FRUITS AND VEGETABLES then browning of the juice could occur. The addition of analine or trypto- phane caused immediate browning. Balls and Hale found that sulfhydryl compounds, some of which occur in common foods, prevent browning of apples. Gluthathione and cystein prevent darkening of the apples even when applied in very dilute concen- tration. Pineapple juice contains a sulfhydryl compound which is the cause for its inhibition of development of brown color. Oxidation and color loss. A type of oxidation that causes fading of red fruits in canning is explained by Kohman and Sandborn. All fruits and vegetables use oxygen in respiration, and some oxygen is found within the fruit or vegetable. The color of strawberries is deadened if they are heated very rapidly after refrigeration, during which the respiratory processes have been inhibited. However, if they are heated slowly so that the interior oxygen is used in respiration the color remains bright. Sulfur Compounds of Plants Sulfur compounds are present in the plant in three forms : in the amino acids of proteins, i.e., cystine, methionine, and others ; volatile compounds ; and sulfates. It is known that a portion of the protein sulfur is readily split off at boiling or higher temperatures. Peterson found volatile sulfur in clover, beet tops, blue grass, and milk. This was unexpected, and he suggests that it may come from two sources, volatile sulfur compounds in the materials used, or from the. splitting off of sulfur from the protein and the formation of hydrogen sulfide. He thinks the latter the more probable explanation. He found a larger percentage of volatile sulfur compounds in plants grown in a sulfur-rich soil than in those grown in a sulfur-poor soil.