| 1. Determination of acidity and the total numbers of lactic acid bacteria in yogurtwith different storage timesIn this experiment,four bottles of yogurt for every different storage time were stored at a temperature of 4℃ for storage periods of 0, 3, 6, 9 days (after the date yogurt was out of factory).The acidity of yogurt were determined in the way of acid-alkline tittering. Total numbers of bacteria were determined in MRS medium using the method of diluting plate counts.The experiment were repeated three times.The total number of bacteria in yogurt without storage was 1.41×l06CFU/ml. Compared of that of control group, the number of bacteria in yogurt with 3 days storage time increased by 864.54%(P<0.01), reaching 1.57×10 CFU/ml. After three days, the number of bacteria was declining.The acitity of yogurt increased rapidly in the first three days of storage period.Compared of that with yogurt without storge, the acidity of yogurt with 3 days storage time increased by 5.85%(P<0.01). After three days, the increasing of acidity was not sharply. The acitity of yogurt with 6d and 9d of storage time increased by 9.04%(P<0.01) and 9.86% (P<0.01)respectively compare with that of yogurt without storage. 2.Effect of yogurt with different storage periods on the immunity system in mice40 mice (male,7-8week old) were divided into four groups.Control Group, Experiment group 1(E1), Experiment group 2(E2) and Experiment group 3(E3) had been fed yogurt without storage, 3d ,6d and 9d(after the date yogurt was out of factory) of storge times respectively on the general diet. Every mice was fed 1ml yogurt successively for 8d .They were killed on the ninth day for the determination of effect of yogurt with different storge times on the transformation of peripheral blood lymphocyte, Phagocytosis of peritoneal macrophages test(MTT)and the secretion of slgA in intestinal .The result of transformation of peripheral blood lymphocyte showed that the SI of experiment El incresed by 19.39% compared that of control group without significant difference.The SI of group E2 decreased by 21.42% compared with that of congtrol without significant difference and the E3 decresed 29.3%(P<0.05).The correlation analyzation between the number of bacteria and SI of lymphocyte was performed. The correlation coefficient was 0.96, P<0.05, showing that there was significant correlation. The result of Phagocytosis of peritoneal macrophagestest(MTT) showed that the activity of Phagocytosis in El increased by 20% significantly than control group. E2 and E3 decreased by 6.67% and 13.3% respectively compared with that of control group, both without significant difference. The correlation analyzation between the number of bacteria and the activity of Phagocytosis of peritoneal macrophages was performed. The correlation coefficient was 0.9946, P<0.01, showing that there was significant correlation. The result of the determination of sIgA in intestinal showed that the sIgA in E1 group increased by 2.43% without significance difference compared with that of control group. The sIgA in E2 and E3 decreased by 12.68%(P<0.05) and 18.57% (P<0.01)respectively. The correlation analyzation between the number of bacteria and the secretion of sIgA in intestinal was performed. The correlation coefficient was 0.885, P=0.115, showing that correlation wasn't significant.3. Effect of yogurt with different storage periods on the immunity system in mice initiatively immuned by Newcastle Disease Virus (NDV)24 mice(male,7-8week old) were divided into four groups. Control Group, Experiment group 1(E1), Experiment group 2(E2) and Experiment group 3(E3)had been fed yogurt without storage, 3d,6d and 9d(after the date yogurt was out of factory) storge time respectively on the general diet. Every mice was fed 1ml yogurt successively for 7d. On the eighth day, all the mice were injected subcutaneously Newcastle Disease Virus 0.2 ml per mouse. Then they were continue to be fed yogurt successively for 10d. On the eighteenth day ,all the mice were killed for the determina...
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