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Ascorbic Acid and Oxidized Flavor in Milk. I. Distribution of Ascorbic Acid and Occurrence of Oxidized Flavor in Commercial Grade a Raw, in Pasteurized Irradiated, and in Pasteurized Milk Throughout the Year¹

ABSTRACT

Samples of commercial grade A raw, irradiated pasteurized, and regular pasteurized milk, taken daily, bi-weekly, or tri-weekly, at time of delivery throughout the year, were titrated daily for four days for ascorbic acid. The 2-6 dichlorophenolindophenol direct titration method of Sharp (6) was used in determining the ascorbic acid values. On the third day of titration the milk was examined for development of the oxidized flavor.

The ascorbic acid content of winter milk was lower than that of spring, summer, or fall milk on the first, second, third or fourth day of storage. Summer milk under conditions of the study usually had more ascorbic acid than spring and fall milk under similar conditions of study, especially on the third and fourth days. Ascorbic acid values for spring and fall milk generally were between the summer and winter values, but varied as to the period of storage.

The average first day values of ascorbic acid in the grade A milk studied were 6.0, 10.5, 8.8, and 7.7 milligrams per liter during winter, spring, summer and fall, respectively. Those for pasteurized irradiated milk were 7.2, 11.1, 14.2, and 10.9 milligrams per liter while those for regular pasteurized milk were 9.9, 12.9, 13.0 and 13.0 milligrams per liter during the same respective seasons.

The rate of disappearance of ascorbic acid, calculated on the third day of titration, when the milk was examined for oxidized flavor, was greater in the winter than in the summer, being relatively greater in the irradiated and in the grade A milk than in the pasteurized milk. Conversely, the stability of ascorbic acid against oxidation was greater in summer than in winter milk.

The stored irradiated milk had a strong oxidized flavor from late fall to early spring. The grade A raw milk had a less pronounced oxidized flavor during this period, but was yet troublesome, whereas no oxidized flavor was noted in the pasteurized milk throughout the year.

The direct titration method of determining the ascorbic acid in milk was found to be very helpful in predicting the presence of a catalyst in commercial bottled milk.

¹ Authorized as Mich. Agri. Exp. Sta. Jour. Article No. 224(n.s.).