| Pumpkin(Cucurbita) is one of the major vegetable crops that has remarkable economic value and health protection function in Cucurbit family.Pumpkin polysaccharide is a kind of substance of bioactivity in pumpkin.It has the effect of lowering blood glucose,antioxidant ability,antitumour and lowering blood lipid,etc.In this paper,Experimental materials collected and purified were inbred lines by our lab,and ultimately aiming is the selection of function pumpkin breed.We studied the extraction, separation and purification of pumpkin polysaccharide and researched the physicochemical properties of different pumpkin breed polysaccharides and different pumpkin polysaccharide fractions extracted continuously in different temperatures condition.The main results are as follows:1.Optimization of technicses of extraction,separation and purification of pumpkin water solution polysaccharide.(1) The factors that affected the extraction of pumpkin polysaccharide included the ratio of material to solvent,extracting time,temperature and times of extracting.A four-factor three-level orthogonal experiment was designed according to the single factor experiments.The biggest influence factor was time,and then temperature and the ratio of material to solvent,the smallest influence factor was times of extracting.The optimal conditions of extracting pumpkin polysaccharide were at the temperature of 70℃, extracting time 4h,the ratio of material to solvent 1:40 and then extracting times of extracting 2.(2) The optimal condition of using ethanol to precipitate pumpkin polysaccharide was the ratio of concentrated solution to ethanol was 1:3.(3) The optimal condition of Sevage mean was ratio of concentrated solution to chloroform-utanol 2:1,shaking 20 min,6 times.2.Physicochemical properties of different pumpkin variety polysaccharidesWe selected four pumpkin strains(coded as strain 1,2,3,4) that have selected by our lab for years,and one pumpkin breeds(coded as breed 5) that was purchased that is a major breed "miben" in marked.The sugar contents of strain 1 and 2 were low and the water contents of them is high.The sugar contents of strain 3,4 and breed 5 were high and the water contents of them were low.The water-solution polysaccharides of strains 1,2,3,4 and breed 5 were named as PX1,PX2,PX3,PX4 and PZ5,respectively.By studying the physicochemical properties of PX1,PX2,PX3,PX4 and PZ5,the results are as follows:(1) The extraction rates of PX1,PX2,PX3,PX4 and PZ5 were 1.02%,1.13%, 1.49%,1.32%and 1.69%,respectively.The neutral sugar contents of PX1,PX2,PX3, PX4 and PZ5 were 23.58%,22.41%,24.51%,24.03%and 35.83%,respectively.The uronic acid content of PX1 was 56.49%that was the highest in five samples.The uronic acid content of PZ5 was the lowest that was only 33.21%.To sum up,the extraction rate and neutral sugar content of the polysaccharide of pumpkin variety that has high sweetness were higher than those of the polysaccharide of pumpkin variety that has low sweetness,but the uronic acid content was not like that.(2) Pumpkin polysaccharides of five breeds were composed of L-rhamnose, L-arabinose,D-glucose,D-galactose and PX3,PX3 and PZ5 had also a little D-mannose. The main monosaccharides of PX1,PX2,PX3 and PX4 were L-arabinose and D-galactose.But the D-glucose content of PZ5 was the highest.So the molar ratios of monosaccharides of five samples were different.(3) Five samples had characteristic absorption peak of polysaccharide.Pumpkin polysaccharide had furan ring and pyran ring and glycosidic bond of them hadαtype.(4) Five samples had the polyelectrolyte effect.[η]values of PX1,PX2,PX3,PX4 and PZ5 were 74.29,60.57,85.77,15.82 and 34.59,respectively.The relation of viscosity average molecular weight of five samples was Mpx3＞Mpx1＞Mpx2＞Mpz5＞Mpx4.(5) The experiment of scavenging hydroxyl radicals(·OH) showed that five samples could scavenge·OH and the scavenging effect became better by increasing of polysaccharide concentration.The scavenging rate of PX4 on·OH was 68.87%when the concentration of pumpkin polysaccharide solution was 3 mg/ml,which represented the best scavenging effect on·OH.The scavenging rate of PX1 on·OH was the lowest,that was 45.91%.(6) The result showed that five samples were active against superoxide radicals. when the concentration of polysaccharide solution was 5 mg/ml,the scavenging rate of PX1,PX2,PX3,PX4 and PZ5 were 14.35%,13.43%,16.67%,14.81%and 13.89%, respectively.(7) The experiment of antioxidant ability of five samples showed that the antioxidant ability of PX3 and PX4 were good,so varieties 3 and 4 are good material of selected functional pumpkin breeds.3.Physicochemical properties of the pumpkin polysaccharide fractions that were extracted continuously in different temperatures condition.The characters of polysaccharide fractions that were extracted continuously in different temperatures condition were studied roundly for the first time.Four fractious of water-soluble polysaccharide,coded as PP1,PP2,PP3 and PP4,were isolated and purified from the fruit of pumpkin at 20℃,40℃,60℃and 80℃,respectively.By studying their characters,the results are as follows:(1) The extraction rate of PP1 was the highest and the neutral sugar content of PP1 was the highest too.But the uronic acid content of PP4 was the highest,which showed the extraction rate of uronic acid was increased by increasing of temperature.(2) PP1,PP2,PP3 and PP4 were all composed of L-rhamnose,L-arabinose, D-glucose,D-galactose with variation of the component ratio.The main monosaccharides of PP1,PP2 and PP3 were L-arabinose and D-galactose and the content of D-galactose was the highest.But the main monosaccharides of PP4 were L-rhamnose and D-galactose and the content of L-rhamnose was the highest.(3) PP1,PP2,PP3 and PP4 showed polyelectrolyte effect.[η]values of PP1,PP2, PP3,and PP4 were 45.54,115.76,120.62 and 155.42,respectively.The relation of viscosity average molecular weight of four samples was Mpp4＞Mpp3＞Mpp2＞Mpp1, which showed temperature was valid mean by which pumpkin polysaccharide was graded and the fractions of high molecular weight were extracted by increasing of temperature.(4) PP1,PP2,PP3 and PP4 had scavenging ability on hydroxyl radicals(·OH) and the scavenging effect became better by increasing of polysaccharide concentration.The scavenging rate of PP1 on·OH was the best.The result showed that four samples were active against superoxide radicals and the scavenging effect of PP1 was the best.(5) PP1,PP2,PP3 and PP4 could inhibit lipid peroxidation in liver homogenate by anti-oxidation and inhibition ability of them became better when the concentration of them were increased.The inhibiting effect of PP1 on lipid peroxidation in liver homogenate by anti-oxidation was the best.Four samples could also alleviate liver mitochondria swelling induced by VC-FeSO4 and the effect of PP1 was the best.(6) The experiment of anti-oxidation activity of four samples showed the anti-oxidation activity of PP1 was the best,so we could conclude that pumpkin polysaccharide faction that had bioactivity could be extracted under low temperature condition.The innovation point of this paper was that the physicochemical properties of polysaccharides of two different type pumpkins were studied,in order to provide the experiment basis and theoretical foundation for the selection of functional pumpkin breed in the future.Physicochemical properties of the pumpkin polysaccharide fractions that were extracted continuously in different temperature condition for the first time,in order to explore the new ways of studying pumpkin polysaccharide.
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