Effects Of Drying Methods On The Physicochemical Properties,Antioxidant Stress And Hypoglycemic Effects Of Polysaccharides In Pumpkin Pulp

In this paper,polysaccharides extracted from pumpkin pulp after treatment in different drying methods(hot air-dried PPe-H,infrared-dried PPe-I,and freeze-dried PPe-F)were studied.To analyze the structural differences of fresh pumpkin pulp under three different drying methods and the antioxidant capacity of fresh pumpkin under different drying methods in vitro and in vivo.To explore the gene regulation related to oxidative stress,and to explore the effect of pumpkin polysaccharides on hypoglycemic function.The main findings were as follows:1.The molecular weights of pumpkin polysaccharides obtained from the three drying methods were 409 k Da for PPe-H,392 k Da and 328 k Da for PPe-I,and 1035 k Da and 169 k Da for PPe-F,respectively.All three pumpkin polysaccharides consisted of glucosamine,glucose,galactose,and xylose.The PPe-H molar ratio was3.56:7.42:1:2.13,PPe-I molar ratio was 2.82:15.44:1:1.25,and PPe-F molar ratio was1.75:5.34:1:2.48.The IR spectra of the three pumpkin polysaccharides showed peaks related to hydroxyl group stretching vibrations at 3400 cm-1 and asymmetric stretching vibrations of methyl carbon-hydrogen bonds at 2930 cm-1.The absorption peak near 1620 cm-1(double bond region)and a weak absorption peak near 1420cm-1 indicate the presence of glyoxalate.A series of peaks near 1000-1367 cm-1indicates the presence of pyranose.The peak at 828 cm-1 indicates the presence ofβ-type glycosidic bond.2.The in vitro antioxidant capacity of the three pumpkin polysaccharides was measured by colorimetric assay in test tubes.The results showed that the three pumpkin polysaccharides had good scavenging effect on DPPH,ABTS,superoxide and hydroxyl radicals with a significant concentration-dependent relationship.3.C.elegans was used as the experimental model to study the antioxidant capacity and the regulation of the expression of antioxidant stress genes in PPe obtained by three drying methods.The results showed that different concentrations of PPe could prolong the lifespan of oxidative stress nematodes to a certain extent.According to the concentration gradient,the average life of PPe-H,PPe-F and PPe-I was prolonged by 23.45%,28.43% and 20.13%,respectively.The content of MDA in nematodes could be reduced by different drying methods of PPe.The content of PPe-H,PPe-F and PPe-I decreased to 0.270±0.003nmol/gprot,0.392±0.009nmol/gprot and 0.339±0.012 nmol/gprot,respectively.PPe obtained by different drying methods could regulate the expression levels of daf-16,sir-2.1,skn-1,sod1,sod2 andsod3 genes in nematodes,thus enhancing the resistance of nematodes to oxidative stress.4.Streptozotocin(STZ)was used to replicate a diabetic mouse model to investigate the effect of drying method on the hypoglycemic effect of pumpkin polysaccharide.The results showed that except for the low concentration(100 mg/kg)of PPe-H,all high and low concentrations of pumpkin polysaccharide significantly reduced serum triglycerides in diabetic mice(p< 0.05).Except for medium concentration of PPe-H and low concentration of PPe-F,all other high,medium and low concentrations of pumpkin polysaccharides significantly reduced serum cholesterol in diabetic mice(p< 0.05).Low concentration of PPe-H and medium concentration(200 mg/kg)of PPe-F significantly increased the serum level of glucagon-like peptide-1(p< 0.05).High concentration(300 mg/kg)of PPe-H,and low concentration of PPe-F both significantly increased liver glycogen content in mice(p< 0.05).Low,medium and high concentrations of PPe-H,medium and high concentrations of PPe-I,and low,medium and high concentrations of PPe-F all significantly increased the GSH content in the liver.High and low concentrations of all three pumpkin polysaccharides were able to significantly enhance hepatic CAT and SOD activities,significantly decrease MDA content in the liver,and significantly decrease hepatic PEPCK activity.High concentrations of PPe-H,low and high concentrations of PPe-I,and medium and high concentrations of PPe-F significantly increased hepatic PK activity.PPe-H with the best antioxidant and hypoglycemic effect was selected from the above studies for the following studies.5.To investigate the effect of PPe-H on glucose tolerance and insulin tolerance in STZ diabetic mice and to analyze differentially expressed genes associated with amelioration of oxidative stress and glucose metabolism disorders by RNA-Seq sequencing.The results showed that medium concentration of PPe-H could effectively improve glucose tolerance in diabetic mice,and both low and medium concentrations of PPe-H could effectively improve insulin tolerance in diabetic mice.In the PPe-H VS negative group,2536 up-regulated and 2151 down-regulated significant differential genes were obtained statistically,and 12 and 17 oxidative stress-related differentially expressed genes and 5 and 7 glucose metabolism-related differentially expressed genes were screened,respectively.