| Pumpkin not only has good nutritive value,the modern study found it also has the effect of lowering blood glucose,lowering blood lipid,lowering high blood pressure,etc.In order to understand more about their structures and functions,the studies were conducted on the extraction,purification, physicochemical properties,chemical modifications,structural analysis and bioaetivity of pumpkin (Cucurbit moschata Duch.).The main results are as follows:1.The pumpkin polysaccharide was extracted by water-extract and ultrasonic method respectively.The best water-extraction conditions are:temperature is 85℃,extraction time is 2.5h,the ratio between material and liquid is 1:20.Under such conditions,the maximum extraction yield(4.31%) can be obtained.The extract contains total polysaccharides 62.59%,and aldonic acid 29.11%.And the content of total polysaccharides,aldonic acid and extraction yield by ultrasonic method was 42.11%,29.24%and 4.03%.2.The five components(WPP1,WPP2,WPP 2-1,UPP1,UPP2) can be obtained from water-extract pumpkin polysaccharide(WPP0) and ultrasonic-extract pumpkin polysaccharide(UPP0) through the precipitation with cetyltrim-ethlammonium bromide(CRAB),DEAE-fiber column chromatography and gel filtration.Through monosaccharide composition analysis,partial acid hydrolization,periodate oxidation, Smith degradation,infrared chromatography,atomic force microscopy(AFM),nuclear magnetic resonance (NMR,1H,13C) of these five components,the main results are as follows:(1) WPP0 is composed of fructose,rhamnose,arabinose,mannose,glucose and galactose.The principal chain of WPP0 is composed of rhamnose,arabinose,mannose,glucose and galactose.The core polysaccharides are rhamnose,glucose and galactose.The terminal residues of branched chain or principal chain are composed of fructose,rhamnose and glucose.The monosaccharide residues of pumpkin polysaccharide consist of pyranose ring.AFM proves that WPP0 consists of chain structure which has several side chains.(2) The average molecular weight of WPP1 is 2.41×10~5Da.WPP1 is composed of fructose,rhamnose, arabinose,mannose,glucose and galactose.The principal chain of WPP1 is composed of rhamnose, arabinose,glucose and galactose.The core polysaccharides are glucose and galactose.The terminal residues of branched chain or principal chain are composed of fructose,rhamnose and glucose and galactose.The chain of WPP1 consists(1→2),(1→3),(1→4) and(1→6) glycosidic bond or branched terminal group.AFM proves that WPP1 consists of chain structure which has several side chains. (3) The average molecular weight of WPP2 is 2.00×10~5Da.WPP2 is composed of rhamnose, arabinose,glucose and galactose.The principal chain of WPP2 is composed of rhamnose,arabinose,glucose and galactose.The core polysaccharides are glucose and galactose.The terminal residues of branched chain or principal chain are composed of rhamnose and arabinose.The chain of WPP2 consists(1→2),(1→3), (1→4) and(1→6) glycosidic bond or branched terminal group.AFM proves that WPP2 consists of chain structure which has several side chains.(4) UPP0 is composed of rhamnose,arabinose,glucose and galactose.The principal chain of UPP0 is composed of fructose,rhamnose,arabinose,mannose,glucose and galactose.The core polysccharides are fructose,rhamnose and glucose.The terminal residues of branched chain or principal chain are composed of rhamnose,arabinose and glucose.AFM proves that UPP0 consists of chain structure which has several side chains.(2) The average molecular weight of UPP1 is 2.08×10~5Da.UPP1 is composed of rhamnose,arabinose, glucose and galactose.The principal chain of UPP1 is composed of rhamnose,arabinose,glucose and galactose.The core polysaccharides are glucose and galactose.The terminal residues of branched chain principal chain are composed of fructose,rhamnose and glucose.The chain of UPP1 consists(1→2),(1→3), (1→4) and(1→6) glycosidic bond or branched terminal group.AFM proves that UPP1 consists of chain structure which has several side chains.(6) The average molecular weight of UPP2 is 2.16×10~5Da.UPP2 is composed of rhamnose,arabinose, glucose and galactose.The principal chain of UPP2 is composed of rhamnose,arabinose,mannose and glucose.The core polysaccharides are rhamnose and glucose.The terminal residues of branched chain or principal chain are composed of rhamnose,arabinose,glucose and galactose.The chain of UPP2 consists(1→2),(1→3),(1→4) and(1→6) glycosidic bond or branched terminal group.AFM proves that UPP2 consists of chain structure which has several side chains.(7) The average molecular weight of WPP2-1 is 1.93×10~5Da.WPP2-1 is composed of glucose and galactose.The principal chain of WPP2-1 is composed of glucose and galactose.The core polysaccharide is glucose.WPP2-1 does not have the terminal residues of branched chain or principal chain.The chain of WPP2-1 consists(1→4) and(1→6) glycosidic bond or branched terminal group.AFM proves that UPP2 consists of chain structure which has half open-ring configuration.NMR shows that the connection mode of terminal residues isα-Gal(1→6),α-Glu(1→4),β-Gal(1→4).3.Pumpkin polysaccharides were sulfated by the means of chlorosulfonic acid-pyridine,sulfuric acid and triethylamine-sulfurtrioxide,respectively.The results showed that chlorosulfonic acid-pyridine method which has higher proportion of sulfate substitution and yield is an ideal way.The optimal condition chosen as extraction time 1 h,temperature 100℃,ratio of pyridine and chlorine sulfonic acid to kelp 1:2.5.4.Pumpkin polysaccharide was carboxymethylated by chloroactic acid in aqueous NaOH.The optimal reaction conditions were determined with the indes of DS.The highest DS is obtained by applying the isopropyl alcohol as reaction medium,the results showed that the method with adding alkali in two steps was better than the method with adding alkali in one step.When solvent was isopropanal, the degrees of substitution of products prepared with the two methods were maximal.In addition,the sequence of adding aetheral reagent could affect the degrees of substitution.The carboxymethylated derivative of pumpkin polysaccharides with high degree of substitution was gained by the method with adding alkali in two steps,the 70%ethanol as medium and appropriate sequence of adding aetheral reagent.5.In vitro antioxidative experiments of 12 different pumpkin polysaccharide(WPP0,WPP0-S,WPP1,WPP1-S,WPP2,WPP2-S,UPP0,UPP0-S,UPP1,UPP1-S,UPP2,UPP2-S,WPP0) indicated that they had the ability to inhibit hydroxyl radicals.The inhibitory effect of hydroxyl radicals increased with the more polysaccharides,but one was weakened through sulfated modification.Pumpkin polysaccharide which did not through sulfated modification has not inhibitory effect of superoxide anion radical,while the sulfate modification one has significant effect of superoxide anion radical.And there is a kind of dose-effect relationship between the clearance rate and the pumpkin polysaccharides by sulfated modification,which proves that introducing chemical group can improve antioxidative activity of polysaccharide.The antioxidative activity of WPPO was much higher than UPPO,which shows that ultrasonic-extraction can influence the composition of polysaccharide.
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