Applied Research On In Vitro Fermentation And Biotransformation Of Citrus Polyphenols

Citrus fruits(CFs)are rich in polyphenols,which have antioxidant,anti-inflammatory,and antibacterial effects.At the same time,polyphenols and their metabolites can maintain the intestinal epithelial barrier,increase beneficial bacteria,inhibit the growth of harmful bacteria,and promote the production of SCFAs and reshapes the role of intestinal flora.However,the polyphenols instability,degradation and metabolism of the upper digestive tract must be overcome,resulting in a decrease of the final concentration of intact PPs in the colon.Dietary fiber can combine with polyphenols to form a hard and complex food matrix to maintain the stability of polyphenols,making it reach the colon to the maximum and become a potential substrate of the intestinal flora.Whether citrus polyphenols will be fermented by commercial lactic acid bacteria to produce beneficial metabolites,especially when there is a complex food matrix,whether there is a correlation between citrus polyphenol metabolism and intestinal microbes,therefore,The important reference value for mining intestinal microbial metabolites that are beneficial to the body and developing functional epibiotic foods through the discussion of citrus gut microbes metabolites and their metabolism laws The main results of this study are as follows:This experiment firstly studied the effect of commercial lactic acid bacteria on the conversion of CFs(grapefruit,kumquat and navel orange)phenolic substances,and comprehensively evaluated the antioxidant activity of the fermentation supernatant in vitro anaerobic fermentation.The results showed that phenolic compounds(hesperetin,naringenin and phenolic acid were degraded p-hydroxyphenylpropionic acid(HPA),3,3-hydroxyphenylpropionic acid,dihydrocaffeic acid(3,4DPPA),4-hydroxyphenylacetic acid,4-hydroxybenzoic acid and other small molecular metabolites by ring fission,dehydroxylation,demethylation,and side chain shortening.In addition,the total short-chain fatty acids,acetic acid and butyric acid were significantly increased in the citrus fermentation supernatant,and the p H value was significantly reduced after fermentation.Finally,the total antioxidant index(APC index)in the citrus fermentation supernatant,and inhibited the oxidative stress of Caco-2 cells induced by lipopolysaccharide(LPS)by significantly reducing the level of reactive oxygen species(ROS)and increasing the mitochondrial membrane potential.By selecting GFP as the research object,the effect of flavanone content and antioxidant activity was evaluated in the presence of food matrix(DF)when subjected to in vitro gastrointestinal digestion.The results showed that the total phenol content and APC index were reduced in the gastrointestinal digestion stage;the flavanone would be retained by dietary fiber and released from the matrix to gut cavity difficultly after digestion.In order to further evaluated the correlation between flavanone metabolites and intestinal microbes in the complex food matrix(DF+GFP),the effects of different DF on GFP flavanone metabolites and intestinal microbes were studied by in vitro colonic fermentation method.The results showed that the distribution of flavanone metabolites was affected by the viscosity of the food matrix,and the growth of low molecular weight compounds(3,4DPPA,HPA,3PPA)were promoted by high-viscosity food matrix(pectin,konjac or chitosan),the populations of Lactobacillus and Clostridium leptum were increased significantly in medium-viscosity food matrix(GFP + konjac/chitosan)group.After 12 hours of fermentation,the acetic acid and propionic acid were increased significantly in GFP +DF groups.The increase of beneficial metabolites and beneficial bacteria indicates that the complex food matrix(DF+GFP)may be a potential functional nutritious food,and medium-viscosity DF(konjac and chitosan)can be used as an important food matrix for polyphenols.