Degradation Of Oat β-glucan By Bio-enzymatic

Oat β-glucan is one of non-starch polysaccharide which is generally existed in endosperm and aleurone cell walls of oat. It has many important physiological functions and is enriched in oat bran. In previous work, it was shown that β-glucan of different molecular weights has different physiological functions. In this study, on the one hand β-glucan was extracted from defatted oat bran successively by extraction, protein removing, and freezedrying, on the other hand β-glucan hydrolase with high activity was obtained by solid-state fermentation. Further, the oat β-glucan was hydrolyzed into low molecular weight β-glucan. Finally, the structure of the hydrolysis product was determined and analyzed by NMR.β-glucan was extracted from oat bran successively by low temperature extraction, high temperature extraction, protein removing, and freezedrying. The yield of β-glucan reached 6%, and the purity was 54%. The hydrolase production was optimized by both single factor experiment and uniform experiment, and the optmium medium composition was as follows: wheat bran 15 g, soybean meal 5 g, glucose 1.2 g, ammonium sulfate 0.16 g, and 20 mL distilled water. When the fermentation was operated at pH 6.5 and 29℃ for 6 d, the maximum hydrolase activity reached 183.27 U/mL.The molecular weights of β-glucan were determined as 4.1×106-7.8×105 by sepharaose CL-4B gel-filtration column chromatography. The polysaccharide-degrading enzyme, produced by Aspergillus niger 3112s, was used to hydrolyze the β-glucan. It was determinated that the molecular weight of β-glucan became lower after hydrolysis, and three different molecular weights of β-glucan were obtained by controlling enzymatic hydrolysis reaction conditions.Finally, structural features of oat β-glucan and hydrolysis products were determined and analyzed by scanning electron microscopy, ultraviolet spectrum, infrared spectrum, and nuclear magnetic resonance spectrum. The SEM analysis showed that the structure of the β-glucan was compact, and the polymerization degrees of the product were decreased and varied in different molecular weights after hydrolysis. Oat β-glucans were (1â†'3) (1â†'4)-β-D-glucan, and the ratio of β-(1â†'-4) and β-(1â†'3) was 2.7:1. The functional groups were unaltered after hydrolysis.