Mixtures of several sulfur amino acid oxidation products were formed in the oxidation of cystine, lanthionine, or homocystine by aqueous hydrogen peroxide in the presence of hydrochloric acid. After 10 min at 100 "C in 6% HzOz and 0.8 N HC1, cysteic acid was the main oxidation product of cystine; lanthionine sulfoxide, lanthionine sulfone, and unidentified products were also formed. In a similar oxidation of lanthionine, lanthionine sulfoxide was the most abundant product; cysteic acid, lanthionine sulfone, and unidentified products were also formed. An identical oxidation of homocystine afforded homolanthionine sulfoxide as the main product; homolanthionine sulfone and homocysteic acid were also formed. When homocystine was oxidized at 50 "C, homolanthionine was the principal product. However, when the HC1 concentration was increased to 4.8 N, homocysteic acid and homolanthionine sulfone were the main products. Sulfoxide produds were distinguished by reduction with dimethyl sulfide in the presence of HC1. Thus, they were converted into their corresponding sulfides and shifted to new chromatographic locations. These desulfurizations by hydrogen peroxide in the presence of HC1 are discussed in relation to known chemical changes of amino acids, including lanthionine formation, which occur in alkali-treated foods and to the use of peroxide in food technology.

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