Two studies were conducted to determine the relative effect of various combinations of antioxidants on vitamin A oxidation and isomerization in nonfat dry milk (NDM). In the first study, one lot of pasteurized unfortified skim milk was divided, fortified with vitamins A and D and one of 11 antioxidant treatments, and spray dried. A control batch from the same lot was also fortified with vitamins A and D and spray dried. Samples were analyzed for total vitamin A bioactivity after zero, one, and two weeks of storage. After two weeks at 50°C, the only NDM samples that did not experience significant vitamin A loss were those treated with butylated hydroxytoluene, either alone at 0.57 ppm or at 0.29 ppm in combination with 250 ppm ascorbic acid. The control sample was significantly different from both of these treatments, and retained only 17% of its original retinol activity equivalents. Isomer composition changed over the two weeks of storage, with an increase of the 13-cis, 9,13-di-cis and the 9-cis isomers as well as a decrease in the all-trans isomer. In the second study, two lots of pasteurized, vitamin A & D fortified, condensed skim milk were divided into four batches, three of which were spiked with an antioxidant treatment: 250 ppm ascorbic acid + 1 ppm propyl gallate, 250 ppm ascorbic acid + 1 ppm butylated hydroxyanisole, or 2 ppm propyl gallate; the fourth batch was a control. Each of the eight batches was homogenized, spray dried and stored in the absence of light at 30°C for 3 months. Vitamin A and riboflavin were analyzed before spray drying, and after 0, 1, 2, 4, 6, 8, 10, and 12 weeks. Two treatments had significant higher vitamin A than the control, the 250 ppm ascorbic acid + 1 ppm butylated hydroxyanisole treatment and the 2 ppm propyl gallate treatment. Limited vitamin A degradation occurred in all samples during the study timeframe, although the overall degree of retinol isomerization began and remained high in all samples, with cis isomers accounting for approximately 23% of the total μg of retinol after 12 weeks. There were no significant differences in riboflavin content between any of the antioxidant treatments and no significant degradation in riboflavin over time. Antioxidants appear to be an effective means of reducing vitamin A oxidation and isomerization in nonfat dry milk. Butylated hydroxytoluene in combination with ascorbic acid was the most effective antioxidant blend observed. Antioxidants may be less effective at protecting against degradation of vitamin A if isomerization has already taken place.



College and Department

Life Sciences; Nutrition, Dietetics, and Food Science



Date Submitted


Document Type





nonfat dry milk, retinyl palmitate, isomerization, antioxidant, riboflavin