Abstract: Objective: To establish a new method for the determination of sulfur-containing amino acids in milk powder by reverse-phase high performance liquid chromatography (HPLC). Methods: Milk powder was subjected to acid hydrolysis or oxidation and subsequent hydrolysis. The optimal hydrolysis conditions and chromatographic separation conditions were investigated. Results: The detection limits of the method for methionine and (Cys)2 were 0.7μmol/L and 0.3μmol/L, respectively, and the linear ranges were both 10－300μmol/L with correlation coefficients of 0.9993 and 0.9992, respectively. In addition, no significant difference was observed between the results of methionine content obtained with acid hydrolysis and oxidation and subsequent hydrolysis, which were both 0.43 g/100 g, whereas the (Cys)2 contents were 0.06 g/100 g and 0.15 g/100 g, respectively, showing a significant difference. Conclusion: Both acid hydrolysis and oxidation followed by hydrolysis can be used for the detection of methionine in milk powder, but only the latter is suitable for the detection of (Cys)2.

Key words: milk powder, lactoprotein, sulfur amino acids, high performance liquid chromatography