| Chlorella contains a variety of bioactive substances,which possess high economic value in agriculture,industry,food,feed and other fields.Chlorella polysaccharides have many functions,such as immune activity,antioxidant activity and cholesterol reduction,so they are widely used as supplements for human nutrition.In this study,the culture conditions of Chlorella were optimized to further improve the yield of its polysaccharides,and the relationship between the different graded polysaccharides and their bioactivities was studied,which laid a foundation for the development and utilization of Chlorella polysaccharides.In order to increase the production of exopolysaccharide in Chlorella,its culture conditions were optimized.The results showed that the optimum conditions for extracellular polysaccharide production in Chlorella were NaNO3 0.9g/L,MgSO4·7H2O 0.3g/L,NaHCO3 0.05g/L and illumination 12hours.Under these conditions,the yield of exopolysaccharide reached 78.98%.The crude polysaccharides were analyzed physiochemically.The infrared spectra showed that the crude polysaccharides were sulfate polysaccharides,and the content of glucuronic acid was 1.60%.Four different molecular weights of Chlorella polysaccharides were obtained by ultrafiltration centrifugation.The molecular weights of Chlorella polysaccharides<10KD,10KD-30KD,30KD-100KD and>100KD were recorded as CEP1,CEP2,CEP3 and CEP4.The antioxidant activities of crude polysaccharides and four fractionated polysaccharides from Chlorella vulgaris were studied.The antioxidant activity of crude polysaccharide CEP was poor,and the scavenging ability of·DPPH and T-AOC and·OH of CEP1,CEP2,CEP3 and CEP4 were higher than that of crude polysaccharide CEP;CEP2 had better scavenging effect on DPPH and the scavenging rate of·OH was 44.52%;CEP3 had 56.61%and T-AOC was51.02%.The crude polysaccharides of Chlorella and four kinds of fractionated polysaccharides had certain inhibitory effects on Escherichia coli,Bacillus subtilis and Bacillus cereus.High molecular weight CEP4 had the best inhibitory effect on Bacillus subtilis,with a diameter of 4.67 mm.The high dose group of CEP3 could better inhibit the growth of Bacillus cereus,with a diameter of 4.65 mm,followed by the high dose group of CEP2.According to measuring the spleen and thymus index of immunosuppressed mice,it was found that the spleen index and thymus index of cyclophosphamide model group were significantly lower than those of normal group and control group.Compared with cyclophosphamide control group,the thymus index of immunodeficient mice was increased in the experimental group（P<0.05）.CEP1,CEP2,CEP3 and CEP4 experimental groups showed better immune effect in the same concentration when compared with the CPE experimental group of crude polysaccharides,indicating that the immune activity of graded polysaccharides was better than rude polysaccharides.The immune level of high dose group of CEP4 was the highest,and the thymus index reached 0.029.The immune effect was increased with the polysaccharide molecular weight,and the immune level increased with polysaccharide concentration.Detection of IL-4 and IFN-gamma in serum of mice showed that the high dose group of CEP4 could significantly increase the levels of IL-4 and IFN-gamma,reaching36.04 pg/mL and 340.56 pg/mL,respectively,indicating that CEP4 had good immune activity.The lymphocyte content of thymus and spleen in cyclophosphamide model group was lower than that in normal group.The content of thymus and spleen lymphocyte in imidazole positive group was higher than that in model group and normal group（P<0.05）.The content of thymus and spleen lymphocyte in each experimental group was higher than that in model group,which indicated that polysaccharides of different molecular weight levels could increase the content of thymus lymphocyte in mice to some extent.The lymphocyte contents of thymus and spleen in CEP4 experimental group（1.13 x 106 and 9.15 x 105）were higher than those in model control group（3.05 x 104 and 6.41 x 105）.The result showed that CEP4 had the best effect on increasing thymocyte and spleen lymphocyte content,and had the best immune activity... |
