| The brewer’s spent grains(BSG), the main byproduct of brewery, contains large amounts of cellulose, hemicellulose, as well as 0.4%(W/W) ferulic acid. Ferulic acid could be ester bonded to oligosaccharides, forming feruloyl oligosaccharides(FOs),a nutritive material with physiological function of both ferulic acid and oligosaccharides. The present study aims to extract FOs from the BSG for its value-increment use.The BSG was grinded with different mechanical treatments, and the alteration in physical space structure, FOs containing material contents, as well as enzymatic hydrolysis efficiency were investigated. Blade grinding followed by ball milling for 30 min was the most effective pretreatment method, with which the particle size of BSG was mainly concentrated in 10 to 200 microns, and the yield of FOs was 14.12%, increased by 14.14% than the untreated BSG sample. With xylanase and cellulose supplemented, the yield of FOs were 39.49% and 50.36%, increased by 23.83% and 50.73% than the unpretreated BSG, respectively. And when synergistically hydrolyzed with xylanase and cellulase, the yield of FOs increased to 64.00%, increased by 36.14% than the unpretreated BSG. The results indicated that with mechanical pretreatment, the tightness and size of BSG were changed, the extractable ferulic acid and xylan were increased, and the hydrolysis efficiency was also enhanced.The effect of 9 different commercial hydrolase on yields of FOs using the pretreated BSG was compared. And the 9th enzyme was finally selected for FOs extraction due to its effective and enzyme constitution. The effects of temperature, p H, substrate concentration, reaction time and enzyme amount on FOs yield were studied. And the results were applied to five factors and three levels of response surface methodology to optimize the FOs preparation process, which was adding 28.48 U×g-1 substrate of 9th enzyme to the solution containing 16.08 g×L-1 of substrate to hydrolyze under p H 6.58, 37 oC for 7.54 h. With this optimum extraction process, the yield of FOs could get to 22.37 μmol×L-1 BSG.The extracted FOs was then purified with macroporous resin. Based on the adsorption effective, the D101 macroporous resin was selected to purify FOs with following optimized protocol: room temperature, sample p H 4.0, sample flow velocity 1.0 m L×min-1, sample quantity 17.34 μmol, water washing for 12 column volume, 50% ethanol eluting for 5 column volume at the velocity of 2 m L×min-1. With this optimum purification process, the recovery of FOs was 82.96%.By ultraviolet spectrum, infrared spectrum and HPLC analysis, FOs was proved to contain ferulic acid that esterified to oligosaccharides, which constitute of xylose and arabinose. Furthermore, the purified FOs exhibited certain capacity of scavenging hydroxyl free radical, H2O2, superoxide anion free radicals and DPPH free radicals. Except for scavenging DPPH free radicals, the antioxidant ability of FOs was superior to that of ferulic acid. FOs also showed strong reducing power, and a certain chelation for metal ions. |
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