Gut Microbiota Compositions And The Characteristics Of The Fermentation As Affected By The Processing Methods And Fiber Types Of Legume

Legumes have a high nutrition value and functional properties,which are regarded as an important source of dietary fiber and then usually used as food in many countries Dietary fiber is the seventh largest nutrient in the human body,which is beneficial to human body health such as reducing cholesterol and blood pressure,promoting intestinal tract health as well as preventing diabetes etc.However,Dietary fiber can not be digested by the human small gut.In fact,it can be partially or completely degraded by large intestinal microflora to produce short chain fatty acid and bring down the pH in the gut,thus improving the intestinal environment.Since beans are processed in different ways,which have different effects on intestinal microflora.The purpose of this research was to study how the processing methods and the types of legumes affect the digestibility,intestinal microbial composition and relative abundance,and microbial metabolites after a simulated in vitro digestion of cooked legume materialsIn this research,we selected Soybeans(Glycine max)and Pinto beans(Phaseolus vulgaris)for study,and respectively studied on the changes of physical and chemical properties and compositions of two types of legumes through autoclaving(high pressure cooking)and a combination of germination and cooking.The effect of the processing methods of the digestibility of soybeans and pinto beans in vitro digestion was also compared.Then the patterns of intestinal microbial producing acids by fermentation of processed legumes after a simulated in vitro digestion were explored The pH values of the in vitro fermented products were measured at an interval of 6 h The sampling times were 0 h,6 h,12 h,18 h and 24 h,respectively and SCFA analysis of the in vitro fermented samples was carried out.The changes of gut microbiota composition and relative abundance was assessed by next-generation sequencing during in vitro fermentation to figure out the relationship between the soluble and insoluble fibers after digestion and intestinal microflora.Besides,our study was also relevant to the potential benefits of the consumption of cooked legumes.The main results were as follows(1)The proximate compositions of bean samples were both affected by the processing methods.For both beans,compared with raw beans,the ash content and the moisture was decreased in processed beans.On the contrary,protein content was increased after processing.As for the lipid contents,there was lower lipid contents in pinto beans processed in two ways.Germination of soybean beans caused a decrease in the lipid contents,while those after autoclaved exhibited an increase in lipid contents For carbohydrates,germination of pinto beans caused a decrease in carbohydrate,while germination of soybean exhibited an increase in carbohydrate.And autoclaving of the two types of the beans showed contrary result.In addition,two processing methods of pinto beans caused a decrease in starch(2)After cooked in two methods,in vitro digestibility of the bean products and the contents of soluble and insoluble fibers after digestion were quite different.The relatively high in vitro digestibility of the bean products was found in autoclaved beans with digestibility of pinto bean and soybean being 75.02%and 73.10%,respectively The digestibility of germinated-cooked soybean and pinto bean was 66.02%and 56.00%,respectively.It was observed that the content of insoluble fibers was higher than that of soluble fibers after digestion(3)The pH changes during in vitro fermentation was contrary to changes of contents of SCFA during in vitro fermentation.The initial pH value of the in vitro fermentation mixture was 8.83,and pH value decreased over further fermentation in all in vitro fermented samples.For those treatments with bean fibers,the pH exhibited a decrease of 1.78-3.73 pH units.Among those treatments,positive control showed a sharp decrease during fermentation.Compared with pH changes,production of SCFA during in vitro fermentation showed an inverse trend.Except insoluble fibers of the pinto beans after germination,all treatments exhibited increase in the contents of acetic acid,propionic acid and butyric acid.In addition,the production of total SCFA was the same as the production of acetic acid,which account for the largest proportion of total SCFA(4)Based high throughput sequencing,the microbial composition and the relative abundance was greatly affected by soluble and insoluble fibers after in vitro fermentation,but the dominant genus were still Fusobacterium,Escherichia and Closrtidium in all treatments.In fact,the insoluble fibers increased the relative abundance of Phascolarctobacterium,while the soluble fibers increased the relative abundance of Prevotella and BacteroidesIn conclusion,the digestibility,the microbial composition and activity was affected,to some extent,by legume type,processing method.A positive modulation of the gut microbiota by the in-vitro digested bean fibers was observed.