Extraction, Purification, Structural Characterization And In Vitro Lipid-lowering Activity Of Polysaccharides From Pomegranate Peel

Pomegranate,a berry belonging to the genus Pomegranate,is widely planted in China and has a long history of cultivation.At present,pomegranate is mainly used for fresh food or juice.Only a small part of pomegranate peel is used for medicinal purposes,and most of the rest is discarded,resulting in a waste of pomegranate peel.The pomegranate peel polysaccharide has a variety of biological activities,such as anti-oxidation,immunity,liver protection and so on.The effect of pomegranate peel polysaccharide on hypolipidemic activity has not been reported.Therefore,the extraction process optimization,isolation and purification,structure characterization and hypolipidemic activity in vitro of pomegranate peel polysaccharide were studied.The main research contents and results are shown as follows.(1)The inner ebullition method was adopted to extract polysaccharide from pomegranate peel.The ethanol concentration,liquid-solid ratio,extraction time and extraction temperature were selected for single factors experiment.The optimal conditions are selected by the response surface method.The results are as follows:ethanol solution concentration of 91%,liquid-solid ratio of 42:1 mL/g,extraction time of 62 min,extraction temperature of 96?,the yield of pomegranate peel polysaccharide was 16.32±0.21%(n=3).This method is simple and can obviously improve the yield of pomegranate peel polysaccharide compared with the traditional hot water extraction method.(2)The pomegranate peel polysaccharide extracted by inner ebullition method was deproteinized,separated and purified by cellulose DEAE-52 column chromatography and G-100 gel column chromatography.Two components,PPP-A and PPP-B,were obtained.The results of UV showed that the contents of PPP-A and PPP-B were very low in protein and nucleic acid.The results of Congo red test showed that both PPP-A and PPP-B did not contain triple helix structure.FT-IR results showed that PPP-A and PPP-B contained polysaccharide functional groups and pyranose rings.The results of ESEM showed that both PPP-A and PPP-B contained lamellar structure,and the lamellar structure of PPP-B was larger than that of PPP-A.Mw of PPP-A was 37390 g/mol.Mw of PPP-B was 62210 g/mol.High performance liquid chromatography(HPLC)results showed that the PPP-A composed mainly of galacturonic acid(15.74%),the arabinose(27.80%)and fucose(28.52%),which also contained a small amount of mannose,rhamnose,glucuronic acid,glucose,xylose and galactose.PPP-B is mainly composed of glucuronic acid(15.00%),galacturonic acid(34.76%)and fucose(41.19%),which also contained a small amount of mannose and arabinose.(3)Pomegranate peel polysaccharide had hypolipidemic activity in vitro.The adsorption capacities of pomegranate peel polysaccharide on lipid and cholesterol micelles were 1.88 g/g and 8.72 mg/g,respectively.The adsorption capacities of pomegranate peel polysaccharide on sodium glycocholate and sodium taurocholate were 40.09%and 34.90%,but the adsorption force was weak.Pomegranate peel polysaccharide on cholesterol esterase inhibition of IC50 was 25.00 mg/mL.Inhibiting type was noncompetitive inhibition.The inhibition of pancreatic lipase IC50 was 9.46 mg/mL.Inhibiting type was competitive inhibition.The addition of pomegranate peel polysaccharide decreased the content of a-helix of cholesterol esterase and pancreatic lipase,and changed the secondary structure.Pomegranate peel polysaccharide has fluorescence quenching effect on cholesterol esterase and pancreatic lipase.The quenching types were static quenching.The binding ratio of pomegranate peel polysaccharide to the two enzymes was about 2:1.The interaction between pomegranate peel polysaccharide and cholesterol esterase and pancreatic lipase was spontaneous and the main force was hydrophobic.These results indicated that pomegranate peel polysaccharide had hypolipidemic activity in vitro.The extraction,purification,structure characterization and hypolipidemic activity in vitro of pomegranate peel polysaccharide were systematically studied,which provided a theoretical basis for the further development of pomegranate peel polysaccharide into hypolipidemic functional food in the future,and also provided a new idea for the comprehensive utilization of pomegranate peel resources.