Preparation Of Feruloyl Oligosaccharides And Dietary Fiber From Brewer's Spent Grain Fermented By Aureobasidium Pullulans

The preparation of feruloyl oligosaccharide?FOs?and dietary fiber?DF?by microbial fermentation was an effective method to produce physiologically active products by using fermentation substrate,but the fermentation yield still needs to be improved in the current research.In this paper,FOs and DF were prepared from brewer's grains by optimizing fermentation conditions and their physiological activities were studied by using brewer's grains as raw materials and Aureobasidium pullulans as fermentation strains.?1?The effects of different fermentation methods on FOs content,DF content and enzyme activity were compared,and solid-state fermentation was selected as the optimum fermentation method.The content of FOs and soluble dietary fiber reached the peak at the 4th day,which were 13.03?mol/L and 9.42%,respectively.The activities of amylase,xylanase and C₁ prodused by Aureobasidium pullulans all reached the maximum of 598.12 mU/mL,842.38 mU/mL and 55.73 mU/mL respectively after 4 d of solid-state fermentation.And the activity of protease reached the maximum of 13.87 mU/mL after 6 d.On the basis of solid state fermentation,the brewer's spent grain were crushed to different degrees,and the optimum grain size of the brewer's spent grain was 60 mesh.?2?By the single factor test and orthogonal test,the optimum carbon source,nitrogen source,inorganic salt and their optimum amount in solid medium were determined.Then response surface methodology was used to optimize fermentation conditions for fermentation of brewer's grains by Aureobasidium pullulans.The results showed that the optimum formula of solid culture medium was as follows:6%xylan,4%urea,and 1%KH₂PO₄.The optimum solid-state fermentation conditions were given as followings:inoculation quantity was 12%,fermention time was 4 d and fermention temperature was 29?.Under those conditions,the content of FOs and SDF was 37.47?mol/L and 23.49%,respectively.?3?By HPLC,ultraviolet spectrum and infrared spectrum analysis,FOs was proved to be composed of ferulic acid,xylose and arabinose,and ferulic acid was linked to oligosaccharide through ester bond.It was found that the purified FOs had a strong scavenging effect on DPPH and hydroxyl radicals.When the concentration of FOs was 1 mg/mL,the scavenging capacity to DPPH and hydroxyl radicals reached58.02%and 72.40%,respectively,which was significantly stronger than that of ferulic acid.Furthermore,at the same concentration,the reducing power of FOs was also significantly higher than that of ferulic acid.The results of the effect of FOs on keeping fresh and holding water of aquatic products showed that FOs could significantly reduce the total bacterial count,pH,total volatile basic nitrogen,thiobarbituric acid values,thawing loss rate and cooking loss rate,and improve sensory score.Among them,0.60%FOs had the optimum fresh-keeping and water-holding effect.Besides,FOs could inhibit the proliferation of microorganisms,slow down fat oxidation,and prolong the shelf life of grass carp by 3 days.?4?After fermentation by Aureobasidium pullulans,the water holding capacity,swelling capacity and oil holding capacity of DF of brewer's spent grains were significantly higher than those of DF before fermentation.Furthermore,the results of adsorption study was showed that the adsorption capacity of SDF after fermentation?SDF2?to glucose,cholesterol and NO₂^-was more than 10%higher than SDF before fermentation?SDF1?.And the adsorption capacity of SDF was significantly stronger than that of insoluble dietary fiber?IDF?.After fermentation,the contents of polyphenols in SDF and IDF increased by 26.63%and 13.02%.The results of antioxidant studies in vitro showed that SDF1 and SDF2 could well eliminate DPPH free radicals(EC₅₀ value 6.47 and 9.45 mg/mL),and the reducing power increased gradually with the increase of concentration,which indicated the SDF prepared by fermentation has higher antioxidant activity.The results of SDF on the growth of intestinal microorganisms showed that both SDF1 and SDF2 could promote the growth of Lactobacillus bulgaricus,and SDF2 had a better effect on the growth of Lactobacillus bulgaricus.Compared with SDF1,SDF2 had a more obvious inhibitory effect on the growth of Staphylococcus aureus,and SDF2 could also inhibit the growth of Escherichia coli.