Bioavailability of Vitamins B_1 and B_6 in Foods.

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1. Method for Simultaneous Quantification of Vitamin B_6 Components in Foods : The primary form of vitamin B_6 in plant foods is 5'-O- (beta-D-glucopyranosyl) pyridoxine (PNG) that is incompletely available to animals. A simple high-performance liquid chromatographic method has been developed for the simultaneous quantification of PNG and all B_6 vitamins in various plant foods, using a single column with an isocratic solvent system. This method offered precise results within 40 min. The contents of vitamin B_6 components in several foods, which were obtained by this method, were in good agreement with those reported in the literature.2. Loss of Vitamin B_6 Activity During Food Processing and Cooking : In pyridoxine ascorbic acid (AsA) -Cu^<2+> mixtures and canned juice, the autooxidation of AsA reduced the vitamin B_6 content by 15-20%. Decomposition of Vitamin B_6 in vegetable juices seemed to vary according to the amount of AsA added to the juices. Hence, hydroxylation of vitamin B_6 by hydroxyl radical generated during the autooxidation of ascorbic acid was inferred to cause the 10-20% loss of vitamin B_6 in plant foods during food processing and cooking.3. Vitamin B_1 Conjugate in Plant Foods : Vitamin B_1 in plant foods except for soybeans, green soybeans and purple laver (rice bran, mustard powder, wheat flour, wheat germ, natto and sesame seeds) exsists as thiamin and its phosphate esters. Thiamin glycoside was not detected in all food samples tested. An unidentified vitamin B_1 conjugate was found in whole soybeans and defatted soybeans. The isolation method and chemical structure of the compound remains unsettled.