Lactic Acid in Dairy Products. IV. Effect of Storage of Evaporated Milk on Lactic and Formic Acid Production, on Ph, and on Acidity and Formol Titrations

Abstract

Fresh commercial lots of evaporated milk, stored at 35[degree], 70[degree], 100[degree] F for 7 months and at 120[degree] for 6 months, were examined at monthly intervals for lactic acid by the Hillig method. Storage of the milk at the 3 lower temps. resulted in slight increases in lactic acid of 1.1, 1.7, and 2.4 mg. per 100 gm., respectively; storage at 120[degree] resulted in an increase of 14.6 mg. per 100 gm. However, the evaporated milk stored at 120[degree] had deteriorated beyond the marketable stage at the end of 2 months. In an additional expt. in which evaporated milk was stored at 100[degree] for 7 months, lactic acid changes were again insignificant, but marked increases occurred in titrable acidity and formic acid, accompanied by a decrease in pH. Titrations of oxalated samples revealed much larger acidity changes than were obtained by the standard titration procedure. Formol titrations were inappreciably affected by storage. The formic acid, determined essentially by the A.O.A.C. distillation procedure, constituted a significant portion of the total acid produced in evaporated milk as a result of storage. When the formic acid was corrected for the fact that only 66.5% recovery is obtained by the method used, it was found to be equivalent to 71.3% of the total acidity increase as detd. by titration. The formic acid content of the fresh evaporated milk samples averaged 11.8 mg. per 100 gm. on the corrected basis.