The Mechanism And The Release Of Grape Seed Polyphenols By Solid-state Fermentation Of Fungi

A large number of grape pomace by-products are produced in the wine production process,but its resource utilization is currently very low.How to realize the resource utilization of grape pomace is one of the important issues that need to be resolved in the healthy and sustainable development of the wine industry.Grape pomace,especially the large amount of polyphenol resources remaining in grape seeds,has high application value,low extraction rate of pomace polyphenols is the main limiting factors for its resource utilization.Based on this,the topic firstly evaluated the proportion of different forms of polyphenols,phenolic substance composition and biological activity in grape seeds of different varieties,and secondly selected microorganisms that can promote the release of grape seed polyphenols through solid-state fermentation and extraction rate of seed polyphenols.The relationship between carbohydratehydrolysis enzyme activities and phenolic contents during fermention was analysed,Moreover,to further elucidate the enzymatic mechanism of solid-state fermentation to promote the release of polyphenols,commercial enzymes were used to release the polyophenols of grape seeds.The preliminary exploration provides a theoretical reference for the resource utilization based on polyphenols of wine grape pomace.The main findings are as follows:(1)The content of free polyphenols of eight grape seeds ranged from 81.32 mg GAE/100 g to 1704.92 mg GAE/100 g,the content of conjugate polyphenols ranged from 105.25 mg GAE/100 g to 2242.62 mg GAE/100 g,and the content of bound polyphenol ranged from171.54 mg GAE/ 100 g to 874.53 mg GAE/100 g,there are significant differences between the content and proportion of three types of polyphenols in different varieties,the main polyphenols were conjugated polyphenols in most of varities of grape seeds,however,bound polyphenols was the predominant phenolics in the grape seeds of Cabernet Gernischet and Matheran.The in vitro antioxidant activity and the inhibitory effect on α-glucosidase of the three types of polyphenols from eight grape seeds are significantly different,but a significant positive correlation was found between the bioactivities and the content of total and individual phenolics of grape seeds.(2)The selected 4 strains can all promote the release of polyphenols of grape seed to a certain extent.Among them,the solid-state fermentation of Monascus can maximize the soluble polyphenol content of grape seeds,and the soluble polyphenols of grape seed can be increased by 6.42 times and the bound polyphenols increased by 1.19 times after fermentation.the chlorogenic acid in soluble polyphenols increased by 340 times,the contents of p-coumaric acid,proanthocyanidin B1 and resveratrol of the bound polyphenols increased significantly and the antioxidant activity of soluble polyphenols and bound polyphenols after fermentation was significantly improved.(3)There was a significant positive correlation between α-amylase,β-glucosidase and total cellulase activities produced of Monascus during the fermentationa and the release of total soluble phenolics of grape seeds(P<0.05),while the correlation between xylanase and pectinase and the release of total soluble phenolics from grape seeds was very low.Commercial enzymes include cellulase,tannase,β-glucosidase,α-amylase and pectinase were used to release phenolics of grape seeds.Cellulase,tannase,β-glucosidase and low concentration of α-amylase except for pectinase can promote the release of polyphenols of grape seeds.Compared with a single enzyme,treatment with complex enzymes is more effective(the soluble polyphenols are increased from 59.16 mg GAE/100 g to 179 mg GAE/100 g).After the complex enzyme treatment,the content of gallic acid,chlorogenic acid,syringic acid,coumaric acid increased significantly.