Determination of Degradation Products of Ascorbic Acid

Abstract

Summary The 2,4-dinitrophenylhydrazine test for ascorbic acid was used to determine both ascorbic and gulonic acid in milk. Data are presented in support of the validity of the test and simplification of procedure. Comparisons are also made with the 2,6-dichlorophenolindophenol reduction procedure. Interpretation of the observed phenomena is made in view of other known facts found in the literature. One- to two-day-old raw milk was found to contain small quantities of gulonic acid. Immediately following pasteurization, the gulonic acid content was also found to be low, but upon storage at 40° F. it increased considerably. Analysis of nonfat dry milk failed to reveal any gulonic acid, regardless of source of the powder, and only questionable amounts were found in evaporated milk. Temperature of storage had a decided effect on the decomposition of dehydroascorbic acid and the rate of oxidation of the resulting gulonic acid in sterile milk. The oxidation of gulonic acid was generally found to proceed rapidly at elevated temperatures. Evidence is presented that exposure to sunlight and copper catalyzed the oxidation of gulonic acid, but not nearly to the same extent as elevated temperatures. The rate of formation of gulonic acid under these conditions was greater than its oxidation.