HPLC DETERMINATION OF THIAMIN AND RIBOFLAVIN IN SOYBEANS AND TOFU

A high-performance liquid chromatographic (HPLC) methodology has been developed to determine thiamin and riboflavin in soy products. An aqueous reversed-phase C18 system with fluorescence detection was employed. Sample preparation included acid hydrolysis and an oxidation step to produce thiochrome from thiamin. Fluorescent chromatograms indicated the presence of many other fluorescing compounds in addition to the vitamins. Thus, vitamin contents of soy products are less than reported in the literature with use of the AOAC methods. Consistent recoveries of 84% for thiamin and 95% for riboflavin were routinely obtained in whole soy flour samples. The contents ranged from 6. 26 to 6. 85 and 0. 92 to 1. 10 μ g/g for thiamin and riboflavin, respectively, in three soybean varieties. Examination of the vitamin distribution on the processing of tofu revealed that the ranges of retention of thiamin and riboflavin were 7. 6-15. 7% and 11. 7-21. 1%, respectively. Retention of these water-soluble vitamins in tofu stored in water indicated remarkable losses due to leaching. © 1990, American Chemical Society. All rights reserved.