Study On Physicochemical Properties And Type 2 Diabetes-Related Bioactivities Of Bitter Melon Polysaccharide Fractions

The development of safe and effective hypoglycemic medicine or functional food has attracted lots of attentions in the field of medicine and food.As a typical vegetable in southern China,bitter gourd(Momordica charantia L.)is also accepted as a medicinal plant.Our previous study confirmed the significant hypoglycemic effect of Momordica charantia crude polysaccharides using streptozotocin induced diabetic mouse model.However,the chemical composition and structural feature of Momordica charantia polysaccharide(MCP)still remain unclear.Hot air drying is one of the main processing methods for bitter gourd.The effects of drying precess on the physicochemical characteristic and bioative activity of MCP have not been reported.In view of that,crude polysaccharides from fresh and dried bitter gourd(i.e.FMP and DMP)were isolated,and their physicochemical characteristics,antioxidant activities,inhibititory activity on a-glucosidase and stimulating effects on the glucose uptake of L6 skeletal muscle cell were analyzed.Moreover,the crude DMP were fractionated by DEAE-52 anion exchange column to obtain fractions which were further inverstigated in structural feature and hypoglycemic effect in vitro.The main research contents are as follows:1 Effects of drying process on the physicochemical characteristics and biological activities of polysaccharides from Momordica charantia.Fresh bitter gourd was dried under 45 ? for 20h by hot air.FMD and DMP were respectively isolated from fresh and dried bitter gourd using the methods of hot-water extraction and alcohol precipitation.Comparative analysis between FMD and DMP including physicochemical characteristic,inhibititory activity on a-glucosidase and stimulating effects on the glucose uptake of L6 skeletal muscle cells found that ? both DMP and FMP were mainly composed of galactose and arabinose,and the former showed higher contents of neutral polysaccharide,uronic acid and protein(P<0.05);? the weight-average molecular weights(Mw)of DMP and FMP were respectively 104.97 and 9.38 kDa,and their distribution indexes were respectively 1.35 and 1.13;? the molecular aggregation of FMP was more compact than that of DMP with stronger hygroscopicity,and their thermodynamic properties were close;? the scavenging activities of FMP on DPPH radical and ABTS were significantly stronger than those of DMP based on their IC50 values;? the IC50 values of a-glucosidase inhibition of FMP and DMP were respectively 148.8 ?g/mL and 166.1 ?g/mL,and DMP showed significant stimulation on the glucose uptake of L6 skeletal muscle cell.Dring process markedly reduced the antioxidant activities of polysaccharides from Momordica charantia by changing their physicochemical characteristics,and will affect their hypoglycemic activities.2 Separation and structural characterization of polysaccharide from dried bitter gourd.Crude polysaccharides from dried bitter gourd were fractionated by DEAE-52 ion exchange chromatography for three main fractions which were named as neutral polysaccharide MCP1,acidic polysaccharide MCP2 and MCP3.GC-MS measurement indicated that MCP1 and MCP2 were mainly composed of galactose and arabinose,and MCP3 was mainly composed of galactose and xylose.Their protein contents were 0.42%,0.81%and 0.17%,resepectively.FIRT combined with and NMR confirmed that the three polysaccharide fractions is mainly composed of a-glycosidic bond.Laser light scattering combined with molecular exclusion chromatography determinedthat the weight average molecular weights of MCP1-3 were 33.38kDa,79.23 kDa and45.39 kDa,and their dispersion indexes were 1.451,1.283 and 1.837,respectively.Their molecular size were in order of MCP2>MCP1>MCP3.The exponent v values of equation<S2>z1/2= k Mwv of MCP1-3 were respectively 0.62,0.34 and 0.35.Three polysaccharide fractions obtained by separation and purification from bitter melon have differences on the chemical composition and structrue.3 Evaluation on the hypoglycemic activities of polysaccharide fractions of dried bitter gourd.MCP1-3 showed no significantly cytotoxicity on L6 skeletal muscle cells at the dose less than lmg/mL.The stimulating effects of MCP1-3 on the glucose uptake of L6 cells in the dose range of 100-1000 ?g/mL were evaluated by glucose oxidase method The content of free glucose in insulin group was significantly lower than that of control group(P<0.05.Only MCP2 and MCP3 could effectively stimulate the glucose uptake of L6 cell.The effect of MCP2 was in a dose-dependent maner,and that at 1000 ?g/mL was comparable to the effect of insulin(p>0.05).MCP3 showed the strongest activity at dose of 800 ?g/mL.Moreover,MCP1-3 could inhibite the activity of a-glucosidase,and their IC50 values were 60.2,720.3 and 748.7 ?g/mL.It was suggested that the hpyerglycemic mechanism of MCP1 was different from those of MCP2 and MCP3.