| Mung bean(Vigna radiata(Linn.)Wilczek.)is a common herbaceous plant of Leguminosae sp..As one of the main grain beans in China,mung beans are grown in most provinces and cities of China.Mung beans are rich in nutrients,which have the effects of anti-oxidation,lowering blood sugar and lipids,anti-cancer and clearing heat and detoxifying.Mung bean skin generally refers to a kind of skin obtained by mung bean after foaming,repeated rubbing and drying,which is called mung bean coat in traditiortal Chinese medicine.Mung bean skin accounts for 7%-10%of the total weight of mung beans,and it contains a variety of biologically active ingredients.However,as of now,mung bean skin has not been fully utilized as a waste during the processing of mung bean by-products.Polysaccharide is an effective active ingredient of mung bean and mung bean skin.Few studies have shown that mung bean and mung bean skin polysaccharides have in vitro antioxidant effects.At the same time,current researches have shown that non-starch polysaccharides can be degraded by the intestinal flora to produce short-chain fatty acids,and have a certain effect on the composition of the intestinal flora.However,the effect of mung bean skin polysaccharide on intestinal microorganisms in mice has not been reported.In this paper,mung bean and mung bean skin are used as raw materials,the biochemical techniques and animal test models were used to study the physicochemical and antioxidant properties of mung bean and mung bean skin polysaccharides.The effects of mung bean skin polysaccharides on the intestinal flora of mice were also explored.It provided a theoretical basis for the further development and utilization of mung bean and mung bean skin polysaccharides.The main findings are as follows:1.Mung bean polysaccharide was obtained by the method of water extraction and alcohol precipitation,and their physicochemical,functional and antioxidant properties were studied.The chemical composition showed that mung bean polysaccharide is mainly composed of neutral sugar(33.05±0.10%),uronic acid(25.83±0.04%)and a small amount of protein(3.17±0.36%).Analysis of physicochemical properties showed that mung bean polysaccharide is a heteropolysaccharide with good thermal stability composed of Ara,Glc,Xyl,Gal and GlcA(molar ratio of 0.94:0.37:0.33:0.13:5.99)with a molecular weight of 146.22 kDa.Analysis of the functional properties showed that mung bean polysaccharide had good hydration properties and oil-holding capacity.Its water solubility index,water holding capacity and oil holding capacity were 88.80±2.52%,4.80 ± 0.39 g water/g sample,3.45±0.16 g oil/g sample.In vitro antioxidant experiments showed that mung bean polysaccharide exhibited good DPPH free radicals and hydroxyl radicals scavenging activities.When the concentration of polysaccharide reached 2.0 mg/mL,the clearance rate was the highest,all reached more than 80%and the free radical scavenging rate was directly proportional to the concentration of mung bean polysaccharide solution.2.Two water-soluble mung bean skin polysaccharides were obtained by cellulase-assisted extraction and hot water extraction,respectively.The physicochemical and antioxidant properties of two mung bean skin polysaccharides were studied and compared.Both polysaccharides were primarily composed of neutral sugar(56.74±0.14%,63.43±0.14%),uronic acid(29.95±0.04%,25.83 ±0.17%)and a small amount of protein(0.53%±0.11,2.13±0.10%).The molecular weights of MBP-1 and MBP-2 were 139 kDa and 208 kDa,respectively.The monosaccharide compositions of the two kinds of monosaccharide were slightly different.MBP-1 was mainly composed of Rha,Ara,Gal,Glc,Xyl,Fru and GalA,the molar ratio was 0.11:1.09:0.52:2.61:0.33:0.31:1.29,while MBP-2 was composed of Rha,Ara,Gal,Glc,Xyl,Man and GalA,the molar ratio was 0.15:0.67:0.29:3.64:0.22:0.12:1.11.Both MBP-1 and MBP-2 were amorphous polymers with smooth surfaces and good thermal stability.Thermogravimetric analysis showed that MBP-2 has better thermal stability than MBP-1.The antioxidant activities of MBP-1 and MBP-2 were analyzed and compared with four aspects:DPPH,hydroxyl,ABTS+free radical scavenging activity and reducing power.MBP-2 had better free radical scavenging activity and reducing power than MBP-1.When the concentration of polysaccharides were 2.0 mg/mL,the DPPH free radical scavenging rates of MBP-1 and MBP-2 were 87.76%,88.09%;the hydroxyl free radical scavenging rates were 67.54%,69.84%;the ABTS+free radical scavenging rates were 73.52%,92.91%.3.Balb/c mice were used as animal models to study the in vivo fermentation characteristics of mung bean skin polysaccharide.The effects of mung bean skin polysaccharide on the intestinal health of mice were investigated from three aspects:colon length,colon index,the changes of short-chain fatty acids in the feces and contents of the colon,and the changes of fecal flora.Gavage of polysaccharides increased the colon length and the production of short-chain fatty acids in mice.The medium-dose group showed obvious advantages both in total short-chain fatty acids(feces,colon contents)or single short-chain fatty acids(except fecal isovaleric acid,propionic acid of colon contents).This indicated that mung bean skin polysaccharide is likely to improve the intestinal microenvironment and benefit for the intestinal health of mice through the short-chain fatty acids produced by fermentation.Alpha diversity analysis showed that the Chaol index and ACE index increased with the increase of polysaccharide concentration.Compared with the control group,the Chaol index of the high-dose polysaccharide group increased significantly(P<0.05).The ACE index in the medium and high dose groups increased significantly(P<0.05).This indicated that certain concentrations of polysaccharides can increase the community richness of mice.The gut microbiota of mice was mainly composed of 9 phylums and 27 genus.Bacteroides and Firmicutes were the dominant phylum,and mung bean skin polysaccharides can increase the abundance of Firmicutes,Bacteroides,Clostridium and reduce TM7 to regulate the composition of gut microbiota,thereby maintaining intestinal health. |
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