Effect Of Trichoderma Viride Fermentation On The Physicochemical Properties And Anti-diabetic Activities Of Dietary Fiber From Tea Residues

Type 2 diabetes(T2D)not only poses a serious threat to people’s health,but also causes a great burden on social economy.At present,drug therapy is mainly used to delay the process of T2 D,but at the same time,it also possesses some serious side effects to patients.A large number of studies have shown that dietary fiber(DF)intake could improve T2 D,however,most of them only investigated the hypoglycemic mechanism of soluble dietary fiber(SDF)or insoluble dietary fiber(IDF).Tea residues,a by-product not fully utilized in tea beverage manufacturing industry,contain a great quantity of nutrients,especially DF.Nevertheless,the SDF contents of tea residue dietary fiber are too low to play a good function.Therefore,tea residues are usually burned or dumped in landfills as industrial waste,resulting in environmental pollution and waste of resources.In this study,we aimed to extract the dietary fiber from tea residues by Trichoderma viride fermentation method and optimize the fermentation conditions using response surface methodology.The effects of fermentation on the structural characteristics,physical and chemical properties and in vitro functional activity of dietary fiber from tea residues were evaluated.Using a rat model of T2 D,the effects of dietary fiber intervention from tea residues before and after fermentation on health improvement in diabetic rats were comparatively investigated.Finally,the potential mechanism of dietary fiber on hypoglycemia in type 2 diabetic rats was explored from metabonomics and intestinal flora.The study was aimed at improving the added value of tea processing by-products and also providing a theoretical basis and technical guidance for dietary therapy of diabetes.The main study contents and results are as follows:(1)The effects of Trichoderma viride fermentation on the structure and functional properties of dietary fiber from tea residues were explored.The response surface methodology identified that the optimal fermentation conditions for the preparation of tea residues soluble dietary fiber(F-SDF)by fermentation with Trichoderma viride were as follows:fermentation time 43.59 h,p H 5.46,inoculum size 10.34%,under which condition,the yield of F-SDF was significantly improved to31.56% compared with that of untreated tea residues dietary fiber U-SDF(4.3%).In terms of fermentation effects on structural aspects of SDF,it was found that Trichoderma viride fermentation made SDF looser with more holes and cracks,increasing the specific surface area by SEM analysis.FT-IR analysis showed that the overall functional groups of F-SDF and U-SDF were basically similar,both had the characteristic absorption peaks of polysaccharides,and the fermentation might destroy the β-glycosidic bonds of pectin and part of polysaccharides.In addition,fermentation changed the monosaccharide composition of SDF and increased the xylose and uronic acid contents by chemical composition analysis.The results of X-ray diffraction and TGA analysis showed that the crystallinity and thermal stability of SDF were significantly higher than those of U-SDF.In terms of the effect of fermentation on the functional properties of SDF in vitro,The ability of F-SDF to absorb cholesterol,sodium cholate,and adsorb glucose as well as the binding capacity for heavy metal ions in vitro were significantly stronger than those of U-SDF.The above results indicated that fermentation could not only degrade part of hemicellulose to significantly improve the SDF content in tea residues,but also improve the structural characteristics and enhance the functional properties.Therefore,the preparation of dietary fiber from tea residues by fermentation with Trichoderma viride is a valuable modification method.(2)The potential hypoglycemic effects of tea residues dietary fiber(TDF and FDF)before and after fermentation on high-fat diet and streptozocin-induced type 2diabetic rats were investigated.The results showed that both FDF and TDF interventions could alleviate the symptoms of polydipsia,polyphagia,weight loss and glucose intolerance in T2 D rats.Moreover,FDF and TDF also could reduce fasting blood glucose(FBG)values,the levels of glycated serum protein(GSP),insulin,lipids(total cholesterol(TC),triacylglycerols(TG),high-density lipoprotein cholesterol(HDL-C),＿low-density lipoprotein cholesterol(LDL-C)and non-esterified fatty acid(NEFA)),improved insulin resistance(homeostasis model assessment-insulin resistance(HOMA-IR)and quantitative insulin sensitivity check index(QUICKI))and oxidative stress(superoxide dismutase(SOD),glutathione peroxidase(GSH-Px)and malondialdehyde(MDA))in T2 D rats.In addition,FDF and TDF interventions showed some improvement effect on the pathological damage of pancreatic islets and liver in T2 D rats,and FDF improved liver function more significantly than TDF.The results indicated that the hypoglycemic and hypolipidemic functions of FDF were better than those of TDF,and fermentation could enhance the hypoglycemic effects of dietary fiber from tea residues on T2 D rats.(3)Based on UPLC-Q-TOF/MS method,the effects of TDF and FDF on serum metabolites in T2 D rats were investigated.The results showed that the different treatment groups were all significantly separated in PCA coordinates.In addition,metabolites such as bile acids,acylcarnitines,and D-phenylalanine were significantly up-regulated in diabetic rats compared with normal rats.After FDF intervention,the contents of saccharopine,histidine,L-Dopa,ketoleucine,etc.were up-regulated.After TDF intervention,the levels of oxoglutaric acid,and L-Dopa,etc.were Up-regulated,the levels of bile acids,etc.were down-regulated,suggesting that TDF could regulate bile acid synthesis and then improve cholesterol metabolism.FDF intervention significantly improved phenylalanine,tyrosine and tryptophan biosynthesis compared to TDF,as metabolites such as L-homophenylalanine were down-regulated,and metabolites such as glycerophosphocholine and saccharopine were up-regulated.(4)The effects of TDF and FDF on intestinal flora in T2 D rats were investigated using Illumina Mi Seq platform.The results showed that FDF intervention significantly increased intestinal flora richness in diabetic rats,whereas TDF did not have this effect.Moreover,after FDF intervention,the composition of intestinal flora in diabetic rats could be improved,and the relative abundances of Proteobacteria,Desulfovibrionaceae,Lactobacillaceae and Clostridiaceae were mainly significantly down-regulated;S24-7,Prevotellaceae,Ruminococcus and Prevotella were significantly up-regulated.PICRUSt prediction analysis showed that the expressions of energy metabolism,glycan biosynthesis and metabolic metabolic pathways were significantly up-regulated after FDF intervention.Moreover,FDF intervention significantly increased the contents of total short chain fatty acids(SCFAs),acetic acid,propionic acid,butyric acid and valeric acid in feces of T2 D rats,as well as significantly adjusted the p H value to the level of normal rats.The levels of total SCFAs,acetic acid and valeric acid and PH value were significantly increased after TDF intervention,however,the effect of TDF was not evident with FDF.The results indicated that fermented FDF had a better ameliorative effect than unfermented TDF on colonic intestinal flora disturbance in T2 D rats.In conclusion,the study demonstrates that the preparation of tea residues dietary fiber by fermentation with Trichoderma viride is a reasonable and valuable modification method,which not only improves the structural and functional properties of dietary fiber,but also improves the health improvement of T2 D rats,and enhances the regulation of metabolic and intestinal flora in T2 D rats,which provides atheoretical basis for dietary therapy of diabetes,and also provides a theoretical basis for the rational development of high added value products from dietary fiber of tea residues.