Lactic Acid in Dairy Products. III. The Effect of Heat on Total Acid and Lactic Acid Production and on Lactose Destruction

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Abstract
Whole milk and skimmilk, heated in sealed cans at 100[degree]C for periods up to 2.5 hrs., were examined for changes in titrable acidity, lactic acid and lactose. Lactic acid produced by these treatments was from 3 to 7 mg. per 100 gm. of milk and constituted not more than 5% of the total acid formed. Lactose destruction amounted to about 25-30% of the total lactose. Milk, to which was added 0.3% disodium phosphate or 0.3% Na citrate prior to heating, underwent appreciably greater total acid production and lactose destruction on heating, but the lactic acid increase was only 2-3 mg./100 gm. more than in the normal samples. The heating of whey for 2.5 hrs. at 116[degree]C resulted in only 11% as much increase in titrable acidity as in skimmilk, but losses in lactose and increases in lactic acid were similar. The slight influence of heat on the production of lactic acid indicates that proper lactic acid measurements on. fresh concentrated milk products may be relied upon to reveal the quality of the raw milk used in their manufacture.