Structural Characterization,Digestive Characteristics And Biological Activities Of Polysaccharides From Lycium Barbarum

Lycium barbarum polysaccharides(LBPs),as the main active component in Lycium barbarum,has various biological activities such as antioxidant,anti-aging and immunomodulation.Previous studies on LBP were mostly focused on extraction methods and biological activities,followed by studies on structural characterization and activities of single molecular weight polysaccharides,and the exploration of the relationship between molecular weight-structural characterization-biological activities was still lacking.In addition,the digestive properties of LBPs are still unclear.Therefore,this paper systematically investigates the extraction method optimization,separation and structural characterization,antioxidant and immunomodulatory activities,and digestive properties of LBP.The main findings are as follows:1.Process optimization of LBPs preparation by water extraction and alcohol deposition methodThe optimal process conditions for the extraction of LBPs by water extraction and alcohol precipitation were obtained by combining single-factor and response surface experiments,using Lycium barbarum(Zhongning,Ningxia)as the raw material and using the polysaccharide extraction rate as the response value.Under this process,the extraction rate of LBP was 15.58 ± 0.19%,the polysaccharide content was 42.05 ± 1.24%,and the polysaccharide yield was 6.55 ± 0.19%.2.Isolation and structural identification of LBPsThe polysaccharides were separated by ultrafiltration membrane separation technique,and two polysaccharides,LBPs-2(7.481 kDa)and LBPs-3(46.239 kDa),and one oligosaccharide,LBPs-1(1.912 kDa)were obtained.Then,the structures were analyzed by chemical analysis,high performance anion exchange chromatography with pulsed amperometric detection(HPAEC-PAD),Fourier transform infrared spectroscopy(FI-IR)scan,Congo red experiment,atomic force microscopy(AFM)scan and nuclear magnetic resonance analysis.They were all found to have similar chemical composition,monosaccharide type and FI-IR spectra.However,different molecular weights significantly changed their chemical composition ratio and monosaccharide ratio.Among them,LBPs-1 and LBPs-2 consisted mainly of glucose,while LBPs-3 consisted mainly of arabinose,galactose,and glucose.In addition,Congo red experiments showed the presence of triple-helix conformation only in LBPs-2 and LBPs-3,and their presence was verified by AFM.Moreover,NMR analysis showed that the glycosyl residues of LBPs-2 have→4)-β-Galp-(1→,α-Glcp-(1→,→3)-α-Glcp-(1→,β-Glcp-(1→,→3,4)-β-Arap-(1→,→3)-α-Arap-(1→and→4)-α-D-GlcpA-(1→,while the glycosyl residues of LBPs-3 have→-3,4)-α-Arap-(1→,→3,4)-α-Galp-(1→,→3)-α-Galp-(1→,→4)-β-Arap-(1→,β-Arap-(1→,→3,4)-α-Galp-(1→and→3)-α-GlcpA-(1→.3.In vitro antioxidant and in vivo immunomodulatory activities of LBPsTheir in vitro antioxidant activities were evaluated by means of oxygen radical absorbance capacity(ORAC),ABTS+radical scavenging capacity,and superoxide dismutase(SOD)activity.The results showed that LBPs-3 had the highest ORAC and SOD activities,but LBPs-2 had the best scavenging capacity for ABTS+radicals.The reason for this result is that the antioxidant activity of polysaccharides is not determined by a single factor.The biological activities would be contributed to synergistic reaction of several related factors,such as chemical reaction mechanism,chemical composition,monosaccharide composition ratio and molecular weight.In addition,the value-added promoting effects of LBPs-2 and LBPs-3 on T-lymphocytes and macrophages under a zebrafish immune injury model based on Vinorelbine tartrate injection(VTI)induction were also investigated.The results showed that LBPs-2 and LBPs-3 could exert immunomodulatory effects in the zebrafish model by promoting the proliferation of T-lymphocytes and macrophages.4.In vitro simulated digestion of LBPs and its effect on antioxidant activityThe digestive properties of LBPs and the changes of antioxidant activity before and after digestion were evaluated by establishing an in vitro simulation digestion model of LBPs.The results showed that the low molecular weight polysaccharides were more easily degraded during digestion,while the high molecular weight polysaccharides were relatively stable,and the main consumption during digestion was glucose.In addition,the antioxidant activity of LBPs was significantly increased after digestion,which may be related to the increase in the relative content of protein and total phenols.