Structure Elucidation, Nutrition and Analytical Methods of Vitamin B_6 Conjugates in Plant Foods.

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Grains and legumes are regarded as good sources of vitamin B_6 (B_6) for Japanese. B_6 in plant foods, however, is incompletely available to animals because it occurs mainly as bound forms. Reports on the structures of the bound forms are scarce except for 5'-O-( -d-glucopyranosyl)-pyridoxine (PNG).1) Three new B_6 glycosides (A, B and C) were isolated from rice bran (10 kg) by various chro-matographic techniques. A, B, and C were shown to consist of pyridoxine (PN) and glucose (GLc) in 1:2, 1:3 and 1:3 molar ratios, respectively, by -glucosidase hydrolysis and Si-MS data. Gibbs test and ^<13>C-NMR spectral data revealed that A was 5'-O-( -cellobiosyl)pyridoxine (PNC). From the results of the Gibbs color reaction and partial hydrolyses which yielded PNC, B was concluded to be 4'-O-( -D-glucosyl)-5'-O-( b-cellobiosyl)pyridoxine, and C to be 5'-O-( -glucotriosyl)pyridoxine.2) A new type of B_6 conjugate was isolated from rice bran (11.4 kg) by adsorption, ion-exchange and gel-filtration methods. The compound gave PN and Glc by alkaline treatment followed by -glu-cosidase hydrolysis. H-NMR, UV and IR spectral data showed that it was an ester of PNC. The acid (MW, 223) seemed to be a kind of aromatic acid. Its structure is being examined.3) a paired-ion reverse-phase high-performance liquid chromatography was developed for the deter-mination of six B_6 vitamers, pyridoxic acid and PNG, a main B_6 component in plant foods. This procedure showed high reproducibility and could detect 0.5 - 1 ng of these compounds. It was found suitable as a routine procedure for the analysis of animal-and plant-foods within 40 min. The bioavailability of the compounds isolabed was assumed to be comparable bo that of PNG.