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Journal of Dairy Science Vol. 45 No. 7 933-934
© 1962 by American Dairy Science Association ®
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Xanthine Oxidase Activity of Milks in Relation to Stage of Lactation, Feed, and Incidence of Spontaneous Oxidation1

T. S. Rajan2, G. A. Richardson and R. W. Stein

Department of Food Science and Technology, Oregon State University, Corvallis

ABSTRACT

The development of spontaneous oxidation in milk has been attributed to its xanthine oxidase activity (1), copper content (3) and, more recently, to the copper and ascorbic acid content (8).

The data in this report were obtained in conjunction with an extensive study of the role of dihydroquercetin as an antioxidant (4). Xanthine oxidase activity is expressed as the reciprocal of the time, in minutes, required for complete reduction of methylene blue, using xanthine as the substrate (6). Spontaneously oxidized flavors were determined organoleptically and by the TBA test (2), at 48-hr intervals. The TBA values, expressed as µg malonaldehyde per 10 g sample, were derived from a standard curve for malonaldehyde.

Individual milk samples were received at regular intervals from the Field Department, Dairy Cooperative, Portland, Oregon, between February and May, 1960. They were brought to the laboratory within 3 hr after milking.

The scatter diagrams (Figure 1) depict the changes in xanthine oxidase activity as related to the stage of lactation and to the incidence of spontaneously oxidized flavors in milks produced on dry-lot feeding and, subsequently, by the same cows on pasture.

FOOTNOTES

1 Contribution from the Oregon Agricultural Experiment Station. Approved by the Director.

2 Present address: Foremost Dairies Inc., San Francisco, California.






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