The Influence And Mechanism Of Structural Changes In Insoluble Dietary Fiber On Its Gut Microbiota Regulation

Dietary fiber is the main energy source for the gut microbiota,and its complex and diverse structure has a directional regulatory effect on the gut microbiota,which can achieve personalized microbiota regulation and play an important role in improving human health.The complexity of dietary fiber structure is reflected not only in the diversity of fiber chemical structure,including monosaccharide composition,branching structure,degree of polymerization,molecular weight,etc.,but also in the complexity of fiber spatial structure,including micromorphology and pore structure.Different fiber structures form microbial ecological niches suitable for different gut microorganisms,and thus affect different structures of the gut microbiota.Currently,the diversity of dietary fiber chemical structures is well understood,but it is not clear how the complex spatial structure of dietary fiber regulates the gut microbiota.Therefore,this project focuses on dietary fiber from plant cell walls and investigates the regulatory effect of dietary fiber on the microbiota at different structural levels.First,the differences and interactions of soluble dietary fiber(SDF)and insoluble dietary fiber(IDF)in rice bran in regulating the microbiota will be investigated.Then,rice bran is subjected to extrusion treatment to investigate the effects of changes in the spatial structure of IDF on its microbial accessibility and microbiota regulation.Finally,by studying the effects of structural changes in IDF extruded from different plant sources on microbiota regulation,the effects of spatial structure and chemical structure on IDF regulation of microbiota structure are elucidated.The main research contents and results are as follows:(1)The difference and interaction between the insoluble and soluble fractions of rice bran in regulating the gut microbiota.When comparing the in vitro fermentation characteristics of IDF,SDF,and IDF-SDF mixtures,it was found that the fermentation of IDF was not significantly different from that of SDF,and the fermentation of the IDF-SDF mixture was slightly lower than the sum of the two,which is related to the different regulatory effects of the different dietary fibers on the gut microbiota.There was no significant difference in gas production and total shortchain fatty acid(SCFA)production between IDF and SDF,but the proportion of SCFA produced was different,which was related to the promotion of different bacterial proliferation.IDF mainly promoted the growth of Bacteroides and Roseburia and produced a higher proportion of propionate.SDF mainly promoted the growth of Faecalibacterium,Butyricicoccus,and unclassified Ruminococcacea and produced a higher proportion of acetate and butyrate.Scanning electron microscopy observations showed that IDF provided a physical ecological niche for bacteria in the spatial structure during fermentation,with more bacteria attaching to the interlayer and edge of IDF.When IDF and SDF were fermented together,SDF promoted the settlement of more bacteria at the edge of IDF and formed a microbial colony,increasing the microbial accessibility of IDF and promoting the rapid growth of bacteria,mainly Bacteroides.The results suggest that the production of SCFA metabolites and the regulation of gut microbiota by IDF and SDF are mainly determined by the microbial accessibility or ecological niche of the fibers rather than their solubility.(2)The influence of spatial structure modification of rice bran IDF by extrusion on its regulatory effect on gut microbiota: rice bran IDF was modified by extrusion to change its spatial structure,and the modified and unmodified IDF were subjected to in vitro fermentation.Extrusion modification decreased the relative crystallinity of rice bran IDF,increased its hydration properties,and made the bran looser and more friable,resulting in more bacteria adhering to the broken edges and gaps.The newly created structure led to the emergence of a new ecological niche for the microbiota,which promoted the growth of bacteria,mainly Bacteroides,thereby increasing the production of acetate,propionate,and butyrate after fermentation.The highest proliferation of Bacteroides was observed in extruded rice bran IDF with the best expansion ability,the most obvious loose layer structure after solubilization,and the highest increase in SCFA production.These results suggest that the spatial structural changes of IDF induced by extrusion created a new ecological niche for the microbiota,which influenced its regulatory effect and increased the production of SCFAs during IDF fermentation.(3)The effects of structural changes in insoluble dietary fiber(IDF)by compression on microbial regulation.Extrusion modification of rice bran,soybean meal,sweet potato residue,and apple pomace with different chemical polysaccharide structures resulted in different degrees of broken and loose spatial structures,obtaining IDFs with different spatial and chemical structures.The in vitro fermentation results showed that the chemical structure of the different IDFs determined their fermentation characteristics and their regulatory effects on the gut microbiota,while changes in spatial structure had a weaker influence but also significantly altered the regulatory effects on the gut microbiota.Extrusion of rice bran IDF significantly increased the abundance of Bacteroides and Parabacteroides,resulting in a significant increase in the content of acetate and propionate;Extrusion of sweet potato residue IDF significantly increased the abundance of Lachnospira,but resulted in a decrease in the production of SCFAs during in vitro fermentation;Extrusion of apple pomace IDF significantly increased the abundance of Clostridiaceae＿Clostridium and Ruminococcacea;Extrusion of soybean meal IDF significantly increased the abundance of Roseburia.These results suggest that the changes in spatial and chemical structures caused by extrusion modification resulted in differences in in vitro fermentation and regulatory effects on the gut microbiota of the different IDF before and after extrusion.In conclusion,in addition to chemical structure,spatial structure also plays an important role in regulating gut microbiota by IDF.