[Determination of sulfur-containing amino acids in food products]

To define the most accurate method for determination of sulfur-containing amino acids in foods, the possibility was tried of using a method suggested by Moore. The method is based on preliminary oxidation of cystine and methionine by performic acid and transformation of these substances to acid hydrolysis resistant cysteic acid and methionine sulphone. Model experiments and use of foods (wheat flour, grade II, and protein part of chicken egg) demonstrated that exposure of proteins to performic acid brings about oxidation of sulfur-containing amino acids to the hydrolysis-resistant forms which may be defined by chromatography with a greater accuracy. Experiments without preliminary oxidation by performic acid showed that foods experience an appreciable destruction (by 30-60%) of cystine and methionine. Therefore, it is advisable that during studies into amino acids contained by proteins, additional hydrolysis may be performed with preliminary oxidation of the samples by performic acid, which enables the determination of the content of methionine and cystine with a greater accuracy.