| Red jujube is a medicinal and edible fruit with a long history of cultivation in China,which is rich in nutrients and biologically active ingredients.Jujube polysaccharide is one of the important biological active ingredients in jujube,which has antioxidation,antitumor,liver protection and other activities.In recent years,with the continuous development of industry on jujube,it is inevitable that many industrial wastes,such as jujube residue and mud,will be produced.How to effectively use these wastes and create additional economic value is a problem for the industry.Muzao is one of the representative jujubes in the Yellow River Basin.In this study,the residue of Muzao jujube after hot water extraction is used as a raw material to continue to extract polysaccharides by alkaline extraction,and the alkali-extracted polysaccharides are purified,structurally characterized and intracellular antioxidant activity researched.The results of this study are as follows:(1)The polysaccharide(AZMP)was extracted by alkaline from jujube pomace.After deproteinization and decolorization,the yield was 3.3%,and the total sugar content was50.3% as well as the protein content was 4.9%.After FI-IR analysis,it has the characteristic absorption peak of polysaccharides,which belongs to polysaccharide compounds.Also,AZMP has good thermal stability by DSC measurement.SEM observation determined its surface has smooth folds,indicating the strong intramolecular and molecular interaction force and tight bond.(2)After separation and purification,four purified components were obtained,named SAZMP1,SAZMP2,SAZMP3,and SAZMP4,and their average molecular weights were 8.91 k Da,8.23 k Da,9.73 k Da,and 28.94 k Da,respectively.The sugar contents of the four polysaccharides were all above 95%.According to the in vitro antioxidant activity indexes(DPPH radical scavenging rate and hydroxyl radical scavenging rate),two components with strong antioxidant activity in vitro were selected: SAZMP3 and SAZMP4.(3)After structural characterization,the backbone of SAZMP3 concluded 1,4-linked Gal Ap,and its branched chain consisted of 1,3-linked Galp,1,3,5-linked Araf,1,2,4-linked Rhap and its terminals were 1-linked Araf,1-linked Rhap,1-linked Galp;SAZMP4 was also based on 1,4-linked Gal Ap,but 1,2,4-linked Rhap and 1,3,5-linked Araf were branched chains,and 1-linked Rhap and 1-linked Araf are terminals.At the same time,their surface were smooth and had a small amount of folds,which was related to the role of intermolecular polyhydrogen bonds.Moreover,the AFM spectra observed aggregation and assembly phenomenons of the two polysaccharides,which has a great relationship with the content ofuronic acid.(4)Constructing the oxidative stress model of Caco-2 cells with hydrogen peroxide,and then using polysaccharides for pre-protection,and determining the relevant antioxidant indicators confirmed that after polysaccharides pre-protection,cell viability,antioxidant-related enzymes(SOD and GSH-Px)activity were significantly increased,while intracellular reactive oxygen species(ROS)and malondialdehyde(MDA)were significantly reduced,indicating that polysaccharides can effectively prevent oxidative stress,and they may play the pre-protective role by blocking the free radical chain reaction process or activating antioxidant related enzymes.At the same time,the protective effect of SAZMP4 is stronger than SAZMP3,which is related to the large amount of galacturonic acid contained in SAZMP4.In this study,four different jujube polysaccharides were separated from the jujube residue by alkaline extraction.The two jujube polysaccharides with strong antioxidant activity were structurally characterized and their antioxidant activity was studied by using cell models.It can provide a certain theoretical basis for the study of jujube polysaccharides.At the same time,this research also provides new ideas for the comprehensive utilization of jujube resources. |
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