Preparation Of Okra Polysaccharide Fractions Extracted By Water And Alkaline Solution And Modulation Of Gut Microbiota In Mice

At present,some researches have shown that okra polysaccharides possess some biological functions.However,there is a little of reports regarding the effect of okra polysaccharides on gastrointestinal tract.Besides,in the reported studies of polysaccharides on gut microbiota,most of the subjects were polysaccharides with different molecular weights(Mw)or different monosaccharide compositions.There is a lack of comparative study of bioactivity and polysaccharides with similar molecular weights consisted with different monosaccharide.In order to understand the effect of polysaccharides on intestinal ecology,this study optimized the extraction condition of polysaccharides,and investigated correlative structural features and biological activities.Main conclusions are mentioned as follows.(1)Optimization of crude okra polysaccharides extracted from water and alkaline solution.In this paper,the extraction conditions were optimized by hot water and alkaline solution.And purified polysaccharides were selected to further study.Based on single factor experiment and response surface methodology,the optimal condition was obtained.For the extraction of water-extracted polysaccharides,time is 2 h,temperature is 80~oC,and liquid/solid ratio is 1:20.The yield of curde water-extracted polysaccharides is 25.92%after twice extraction.For alkaline-extracted polysaccharides,the pH value of solution was adjusted to 8.5 with sodium hydroxide.With the increases of extraction time(2.5 h)and temperature(85~oC),the yield of crude alkaline-extracted polysaccharides was up to 26.93%.(2)Selection and structural analysis of polysaccharides with similar molecular weights consisted with different monosaccharide.According to results of molecular weights and monosaccharide compositions,the fractions for the subsequent study were water-extracted polysaccharides with Mw of9.12×10~4 Da(WEP),and alkaline-extracted polysaccharides with Mw of 9.79×10~4 Da(AEP).Based on results of monosaccharide compositions,galactose(32.53%)was the most abundance in WEP,followed by rhamnose(19.76%),fructose(17.21%),arabinose(13.38%),glucose(8.94%),galacturonic acid(5.24%)and mannose(2.94%).In contrast,AEP contained mannose(7%),rhamnose(26%),galacturonic acid(17.92%)and galactose(49.08%).In terms of structural analysis and characterization,it found that the structure of water-extracted polysaccharides was complex,and the connection between the molecular chains of alkaline-extracted polysaccharides was compact.(3)The effect of WEP and AEP on gut microbiotaBased on the determination of animal experiments,compared with negative control group,there was an increase in food intake,an elevation of moisture of caecum content,a reduction in concentration of ammonia,a decline of fat absorption.Besides,as improvement of total SCFAs levels,thickness of mucosa and muscular layer increased.In addition,it was found by High-throughput Sequencing analysis that WEP and AEP could improve the abundance and diversity of microbes in caecum,up-regulate the ratio of Lactobacillus,and down-regulate the radio of Bacteroides.Meanwhile,the level of Bacteroides in mice fed with AEP was more lower as compared to those fed with WEP.On the whole,WEP and AEP have effects on intestinal microbiota by the output of detrimental compounds and the supply of nutrients.And AEP supports a more pivotal role in manipulating gut microbiota than WEP.