Breeding Of Grifola Frondosa Fermented Rice Bran And Wheat Bran,and Structural Characterization And Activity Of Grifola Frondosa Polysaccharides

Grifola frondosa is a kind of fungus that can be used as both medicine and food.It is not only rich in nutrients,but also has physiological effects such as anti-oxidation,anti-tumor and immune regulation.Rice bran and wheat bran,as the main agricultural by-products in China,have high yield but low utilization.G.frondosa has the ability to degrade polysaccharides,cellulose and lignin,and can produce more active compounds through metabolic activities.In this study,the biotransformation ability of G.frondosa strains to rice and wheat brans was improved by mutagenesis to produce G.frondosa polysaccharides.The structural composition of polysaccharides was characterized to preliminarily understand the antioxidant and hypolipidemic activity of G.frondosa polysaccharides,aiming to provide a theoretical basis for the exploitation and utilization of rice and wheat brans resources and the study of G.frondosa polysaccharides.The main research contents and results are as follows:(1)Using G.frondosa ZJQYLIU2017 as the parent strain,a mutant strain GFAM10 with faster growth rate and higher bioconversion efficiency of brans was screened out by ARTP-microwave mutagenation breeding.Compared with the parent strain,the growth rate of GFAM10 increased by 28.44%,biomass,intracellular polysaccharides and extracellular polysaccharide increased by 17.66%,17.95%and22.27%,respectively,the decomposition ability of rice and wheat brans was increased by 7.62%,and the gene has stability.During 2-10 d fermentation,the activities of CMC enzyme,pectinase and amylase in the fermentation of GFAM10 were 4.748 U,9.502 U and 19.318 U,respectively.The peak of CMC enzyme activity appeared 2days earlier than that of the original strain,and amylase increased by 13.54%,respectively,which might be the reason why GFAM10 showed better decomposition ability of brans.The utilization of cellulose and pectin by GFAM10 was mainly in the early stage of fermentation,and the utilization of starch was more in the later stage.(2)Uniform U₁₅(5⁴)experiment was designed with the addition amount of rice and wheat brans,initial pH,shaker speed and fermentation time as single factors,and four regression equation models were obtained.Taking the mycelium of G.frondosa as the main index,the optimal conditions of GFAM10 medium for deep fermentation of rice and wheat brans were as follows:The addition amount of rice bran 8.0g/100m L,wheat bran 2.0 g/100m L,initial pH 4,rotation speed 130 r/min,fermentation time 10 d,the dry weight of mycelium was 3.248 g,mycelium polysaccharide 584.438 mg in 100 m L fermentation media,an increase of 26.14%and58.33%,respectively?(3)G.frondosa polysaccharide was obtained by using rice and wheat brans as fermentation substrate.Three polysaccharides,GFP-W1,GFP-W2 and EP-X1,were obtained by purification of G.frondosa mycelial polysaccharides(GFPs)and exopolysaccharides(EPs).GFP-W2 contained higher polysaccharide content(95.50%)and uronic acid content(19.29%),and molecular weights(M_W)of GFP-W2 was2.733×10⁷ Da.The molecular weights of GFP-W1 and EP-X1 were 9.161×10⁵ Da and2.564×10⁴ Da,respectively.All three polysaccharides are heteropolysaccharides,among which GFP-W1 and GFP-W2 were mainly glucose,and EP-X1 was mainly arabinose.GFP-W1,GFP-W2 and EP-X1 do not have triple helix structure.GFP-W1is dispersed into irregular filaments,and multiple molecular chains are wound to form a uniform spherical polymer.GFP-W2 had a cross-linked filamentous structure,showing spherical particles of different shapes and sizes.The structure list of EP-X1is relatively loose,showing smaller fragments,and basically exists in the form of chain.(4)The antioxidant and hypolipidemic activities of GFP-W1,GFP-W2 and EP-X1 were evaluated.Among them,GFP-W2 showed stronger DPPH radical scavenging ability,while EP-X1 showed stronger ABTS radical scavenging ability,FRAP and cholate sodium binding ability.The results showed that all three polysaccharides showed outstanding antioxidant activity and hypolipidemic activity.