Screening Of Dietary Fiber Fermentation Modified Strain From Tea Residue And Its Effect On Dietary Fiber Modification And Release Of Bound Polyphenols

In recent years,tea beverage factories,tea polyphenol factories and other tea deep processing has produced a large number of tea residues,after the accumulation of very easy to fermentation corruption deterioration.The dietary fiber content in tea residues is very rich,among insoluble dietary fiber accounts for the main proportion,while soluble dietary fiber with better physicochemical properties accounts for less proportion.Tea polyphenols are also the most important active ingredients in tea residues.According to the state of binding with substances,tea polyphenols can be divided into bound polyphenols and free polyphenols.Most of the studies have focused on free polyphenols,while bound polyphenols are neglected due to the difficulty of isolation and preparation.Therefore,using tea residues as raw material to prepare high-quality tea residues modified dietary fiber and release bound polyphenols can not only solve the problems of environmental pollution,but also increase the added value of tea residues.Among many modification methods,microbial fermentation has attracted people’s attention because of its milder conditions,safer and more efficient means.However,there is no special fermentation strain for improving the soluble dietary fiber content in tea residues by fermentation method,which is not conducive to the high-value utilization of tea residues.Based on this,two cellulose-degrading strains were obtained by isolation,purification,pr-screening,re-screening,morphological observation and identification,and the optimal fermentation conditions were determined by response surface methodology to obtain high yield of tea residues soluble dietary fiber,and the effects of fermentation modification on the structural characteristics and functional properties of the produced tea residues soluble dietary fiber were explored.Meanwhile,the release of bound polyphenols and their mechanism were investigated based on UPLC-ESI-QTOF-MS/MS.This study not only reveals the potential use of dietary fiber and bound phenolics in functional food industry,but also provides a basis for the high quality utilization of tea residues by fermentation method.The conclusions of this study are as follows:（1）Two high-efficient cellulose degrading strains,CZ-6 and CZ-7,were obtained through enrichment culture,separation and purification,preliminary screening of cellulose congo red culture medium,and repetitively screening of cellulase activity.The morphological observation and sequence determination results indicated that the CZ-6 strain had the closest genetic relationship with Cochliobolus kusanoi,while the CZ-7 strain owned the closest genetic relationship with Aspergillus puulaauensis.On this basis,CZ-6 and CZ-7 were successfully used to construct composite bacterial strains,which used cellulase activity as an indicator.（2）On the basis of single factor experiments,the Box Behnken response surface methodology was used to analyze the effects of fermentation time,initial p H,and CZ-6 and CZ-7 inoculation ratios on the yield of soluble dietary fiber from tea residue.After three factors and three levels analysis,combined with model results and experimental verification,the optimal mixed fermentation conditions were determined as follows:fermentation time of 112.07 h,initial p H of 4.58,and inoculation ratio of CZ-6 and CZ-7 at 1:2.46.The maximum SDF production was26.50 g/100g.（3）The structural and functional properties of soluble dietary fiber were explored before and after fermentation under optimal mixed fermentation conditions.The results showed that all modified SDF had representative absorption peak of polysaccharides and typical crystal of cellulose type I.In comparison with other groups,soluble dietary fiber prepared by mixed fermentation exhibited more porous and loose structure,higher thermal stability and lower molecular size.Modification treatments not only changed the structural characteristics,but also heightened the adsorption properties.The mixed fermentation-treated samples exhibited enhanced water solubility,water and oil holding capacity,and adsorption capacity for cholesterol and nitrite.Thus,the soluble dietary fiber prepared by mixed fermentation had superior structural and functional properties and improved the quality of dietary fiber.（4）The fermentation release of bound polyphenols from tea residues insoluble dietary fiber and its mechanism were investigated under optimal mixed fermentation conditions.The results indicated that bound polyphenols released by mixed fermentation was significantly higher than untreated group.The structural characteristics and the dynamic changes of the carbohydrate hydrolase activities manifested that the decompose of cellulose and lignin,and the secretion of cellulase were vital for the release of bound polyphenols.Additionally,28 polyphenols components were detected and their biotransformation pathways（hydroxybenzoic acids pathway,hydroxycinnamic acid pathway and benzoic acid pathway,etc）were preliminary speculated.The biological activity assays showed that the bound polyphenols treated by mixed fermentation produced prominent inhibitory activities againstα-glucosidase andα-amylase,as well as it also exhibited significant scavenging effects on DPPH^·,ABTS^+·free radicals and ferric reducing antioxidant power.The results of the study can lay a theoretical foundation for further research on dietary fiber and bound phenolics,and provide a new way for the comprehensive utilization of agricultural by-products.