Study On The Preparation And Hypoglycemic Activity Of Pumpkin Peel Polysaccharide-Chromium(?) Complex

A large number of pumpkin peel by-products are produced in the deep process of pumpkin peel.Polysaccharide is an important active ingredient in pumpkin peel with bioactive activities such as hypoglycemic,antioxidant and anti-tumor activities.Trivalent chromium ions are important component of glucose tolerance factor,which can accelerate the utilization of glucose in the body and has hypoglycemic activity.However,the absorption and bioavailability of chromium depend largely on its chemical form in the body,therefore,developing novel organic chromium(III)supplements with good biological activity is of great interest.Polysaccharide chromium complex has high stability and less side effects,which has the potential to be hypoglycemic products.In this study,pumpkin peel was used as raw material to extract polysaccharide,and combined with chromium chloride under certain conditions to prepare pumpkin peel polysaccharide-chromium(?)complex[PPP-Cr(III)]and optimize the preparation conditions,and the structural characterization,in vitro digestion and hypoglycemic activity were studied.The main study results are as follows:(1)Preparation of PPP-Cr(III):Taking the weight fraction between chromium and polysaccharide,reaction p H,reaction temperature and reaction time as the objects,the influence to the synthesis of PPP-Cr(III)of each factor was determined by single factor experiment and the response surface methodology.The optimal reaction conditions obtained from response surface were as follows:the weight fraction 0.08:1,temperature 60.0°C and p H6.8,the experimental chelation rate was 99.23±0.12%for PPP-Cr(III)under the optimal conditions,which agreed closely with the predicted value.(2)Structural characterization of PPP-Cr(III):The physical and chemical properties of PPP-Cr(?)changed,the contents of total sugar and uronic acid decreased,the average molecular weight decreased and the dispersion coefficient increased.The molecular weight of the PPP-Cr(?)was 1.398×10~6 Da.PPP-Cr(III)was mainly composed of rhamnose,arabinose,galactose,glucose and galacturonic acid,its molar ratio was 0.27:1.72:3.53:89.63:4.86.The scanning electron microscopy showed that the surface of PPP-Cr(?)changed from granular morphology to flaky structure,and from roughness to smoothness.Infrared spectrogram showed that the wavelength of O-H absorption peak shifted and the absorption peak was broadened in PPP-Cr(III),indicating that the coordination of chromium ions with the hydroxyl group of polysaccharide,the absorption peak of C=O shifted to 1744.20 cm^-1,the symmetrical telescopic absorption peak of the carboxyl group,C-O absorption peak,and C-O-C vibration absorption peak were broadened and shifted,Cr-O characteristic peak appeared at 530.34 cm^-1.Circular dichroism spectra of PPP-Cr(III)indicated the conformational changes in the structure of macromolecules.UV absorption spectra indicated that there were no proteins or nucleic acids presented in PPP-Cr(III).The hermogravimetric analysis showed that the thermal stability of PPP-Cr(III)decreased slightly.The X-ray diffraction spectrum indicated that PPP-Cr(III)was typical amorphous material.(3)In vitro digestion study of PPP-Cr(III):The solubility of PPP-Cr(III)in gastric juice and intestinal juice was lower than that of chromium chloride,and PPP-Cr(III)had a certain sustained release effect in the acidic environment of gastric juice,the dialysis rate of PPP-Cr(III)and chromium chloride were 0.78%and 0.16%.To conclude,PPP-Cr(III)has high bioaccessibility.(4)In vitro hypoglycemic activity of PPP-Cr(III):At the concentrations of 0.2,0.4 and1.0 mg/m L,the?-glucosidase inhibitory activity of PPP-Cr(III)was 17.97%,20.34%and21.11%,which was dose-dependent,and the effect was better than that of PPP.PPP-Cr(III)of25,50,100,200?g/m L showed no obvious cytotoxicity to Hep G2 cells;the glucose consumption of IR-Hep G2 cells in the model group was 4.8 mmol/L,the glucose consumption was 5.17,5.52,5.66 and 6.25 mmol/L with the treatment of PPP-Cr(III),which were higher than that of PPP.Moreover,the phosphorylation of AMPK and GSK-3?was enhanced after PPP-Cr(III)treatment compared with the model group.The results showed that PPP-Cr(III)had a positive effect on glucose homeostasis,promoting the phosphorylation of AMPK by activating AMPK,regulating the phosphorylation of the downstream signaling factor GSK-3?mediated by the insulin PI3K/Akt signal transduction pathway,promoting glucose metabolism and improving insulin resistance.The results showed that the PPP-Cr(III)had certain hypoglycemic activity,which can provide theoretical support for the development of new hypoglycemic products.