Fermentation To Synthesize β-Glucan And Oryzanol And The Hypolipidemic Study

β-glucan is a kind of extracellular polysaccharide which is easily soluble in water and has certain viscosity,it can be synthesized by the fermentation of sprouting short-stalked mould,it is colourless,tasteless,has no toxic side effects to human body and has good physiological activity function,so it is widely used in food,cosmetics,medicine and other fields.Oryzanol is a mixture of cyclic lignan congeners and ferulic acid esters of phytosterols,and is the main functional factor of rice bran,rice bran oil,rice germ,etc.It has physiological functions such as antioxidant,scavenging free radicals and lowering blood lipids and cholesterol.In this project,a strain of Aureobasidium pullulans that produces β-glucan and does not produce melanin was used to ferment agricultural by-products such as rice bran to obtain a large amount of physiologically active extracellular β-glucan and to increase the content of oryzanol in the grain.In order to investigate the mechanism of synthesis,the precursor of oryzanol synthesis was added to the basic liquid medium,and the extracellular β-glucan and oryzanol were enriched simultaneously by exogenous addition of metal salts.The effect of the combination of β-glucan and oryzanol on the hypolipidemic effect was investigated.The results of the study showed that the best fermentation of oryzanol was achieved with the addition of 300 mg/L of a mixture of ferulic acid and oryzanol（ferulic acid:oryzanol=1:1）.Compared to the exogenous metal salts Mn²⁺,Fe²⁺and Ca²⁺,the addition of Mg²⁺was more beneficial for β-glucan production and oryzanol biosynthesis during fermentation,and the best results were obtained with the addition of Mg²⁺at 300 mg/L,where the β-glucan production reached（4.46±0.14）g/L,about 3.9 times that of the control,and glutamate synthesis reached（4.25±0.16）mg/L,about 3.9 times that of the control.（4.25±0.16）mg/L,about 3.8 times that of the control group.The resulting crude polysaccharides were isolated and purified and analyzed qualitatively and quantitatively.The addition of Mg²⁺increased the proportion of neutral polysaccharide fractions,enriched the different ionic strength fractions of polysaccharides,reduced the protein content in polysaccharides,and decreased the molecular weight of neutral polysaccharides with 0.2 M NaCl-eluted polysaccharides,but obtained 0.4 M NaCl-eluted polysaccharides with higher molecular weight.This extracellular polysaccharide was characterised as a β-glucan by the composition of the monosaccharide and by FT-IR spectroscopy.The activity of key enzymes involved in the synthesis of β-glucan and oryzanol,gene expression,intermediate product synthesis and energy metabolism were measured in Sprouting stunt mould cells.The addition of Mg²⁺significantly increased the activity of PGM,UGP and β-GS,the key enzymes of β-glucan synthesis,as well as the esterase of glutelin synthesis（p<0.05）;the production and utilization of UDPG,an intermediate product of β-glucan synthesis,was significantly increased（p<0.01）.The intracellular levels of ATP and NADH were significantly increased（p<0.05）,and the expression levels of pgm1,pgm2 and ugp genes were significantly up-regulated.（p<0.01）The two target products, β-glucan and oryzanol,were purified and dried to obtain β-glucan and oryzanol samples with a purity of 96.45%and 91.51%respectively,which were used in the in vitro lipid lowering experiments of β-glucan combined with oryzanol.The in vitro lipid-lowering effect of β-glucan in combination with oryzanol was significantly improved compared with that of the fraction with the corresponding concentration of β-glucan only（p<0.01）.