Preparation,Physicochemical Properties And Lipid Metabolism Regulation Of Polysaccharides From Barley Leaves At Different Growth Stages

Hyperlipidemia is a pathological state of lipid metabolism disorder,which can cause fatty liver,atherosclerosis,acute myocardial infarction and other diseases,and has seriously endangered human health.Barley leaves（BL）,as a medicinal and food homologous plant,has various physiological activities such as lowering blood sugar and blood lipids,anti-oxidation and anti-tumor.Polysaccharides are one of its major active ingredients.In this study,barley leaves polysaccharides（BLP）were obtained from BL at different growth stages.The physicochemical properties,structural characteristics,in vitro biological activities and digestion characteristics of BLP at different growth stages were comparatively investigated,and the highly bioactive BLP was established.On this basis,the in vivo regulation of highly bioactive BLP on lipid metabolism disorder and gut microbiota dysbiosis were evaluated by high-fat diet-induced hyperlipidemia mice model.The main results are as follows:（1）BLPs（BLP-Z12,BLP-Z21,BLP-Z23,BLP-Z28,BLP-Z29,BLP-Z31 and BLP-Z32）were orderly extracted from BL at different growth stages including seedling（Z12,Z21）,tillering（Z23,Z28,Z29）,and stem elongation（Z31,Z32）through alkaline-extraction method.The results showed that yield,total sugar andβ-glucan contents of BLPs ranged from 2.55%to 4.47%,71.75%to 83.22%and18.85 to 81.38 mg/g BLP,respectively.Amongst of the BLPs,BLP-Z23 had the highest yield（4.47%）,total sugar（83.22%）andβ-glucan（81.38 mg/g BLP）content.The molecular weights（M_w）of BLPs were composed of two fractions,and their M_ws ranged from 635.7 to 835.5 k Da and 73.73 to 169.2 k Da,respectively.The BLPs were acidic heteropolysaccharides,and composed of xylose,arabinose,galactose and glucose with different molar ratios,which had similar chemical structural characteristics and different microscopic morphologies.Moreover,BLPs exhibited good in vitro antioxidant activity and in vitro bile acid-binding capacity,but differences were found in their cellular immune activities.Amongst of the BLPs,BLP-Z12 had the highest in vitro antioxidant activity,and BLP-Z21 showed the highest in vitro bile acid-binding capacity（60.29%）and cellular immune activity（3.03μM）.（2）The in vitro digestion characteristics of BLP-Z21,BLP-Z23 and BLP-Z31were investigated by in vitro simulated saliva-gastrointestinal digestion.The results presented that the total sugar,uronic acid,β-glucan and reducing sugar contents of BLP-Z21,BLP-Z23 and BLP-Z31 during digestion reached the maximum in the gastric digestion stage,the protein contents gradually decreased,and the total phenolic contents decreased and then slightly increased.The M_ws of three BLPs initially decreased and then increased,reaching a minimum after the gastric digestion.The monosaccharide composition of three BLPs during digestion were the same,but differed in content.Three BLPs during digestion had similar chemical structural characteristics.Moreover,the in vitro antioxidant activities of three BLPs were weakened（P<0.05）after digestion but the in vitro bile acid-binding capacity of them was enhanced（P<0.05）.Amongst of these digested BLPs,BLP-Z31 after digestion exhibited the best FRAP(27.46μmol Fe²⁺/g sample),TEAC（9.43μmol Trolox/g sample）and in vitro bile acid-binding capacity（80.33%）.（3）The in vivo regulation of BLP-Z31 on lipid metabolism disorder and gut microbiota dysbiosis were investigated by high-fat diet-induced hyperlipidemia mice model.Results demonstrated that compared with the model group,the pre-supplementations with BLP-Z31（200、400 mg/kg BW）not only effectively improved the obesity,organomegaly and fat accumulation in mice caused by high-fat diet,but also ameliorated the levels of lipids,hepatic injury and oxidative stress.Meanwhile,BLP-Z31 could promote the production of short chain fatty acids（e.g.acetic acid,propionic acid,butyric acid and isovaleric acid）in high-fat diet mice.Gut microbiota analysis revealed that BLP-Z31 had no significant effect on the diversity of gut microbiota in high-fat diet mice（P>0.05）,but could regulate the structural composition of gut microbiota.Specifically,BLP-Z31 could increase the relative abundances of Bacteroidota,Muribaculaceae and Lachnospiraceae,reduce the relative abundances of Firmicutes/Bacteroidota and Desulfovibrionaceae,thereby improving the imbalance of gut microbiota in mice induced by high-fat diet.