The Effect And Mechanism Of Several Stress Factors On Endogenous Preservation Of Litopenaeus Vannamei

Stress is the process of changing the survival mode of aquatic animals and forcing pressure to them,including physical,chemical and biological factors. Shrimp physiological activity and responses will be changed under the action of stress, including the endogenous enzyme activity and intestinal microflora, and which been considered closely related with shrimp shelf life after death. Currently, the major stress factors in aquaculture are starvation, microbial agents and calcium stress. To study the role in keeping fresh of these three stresses, and further study the effects of these stresses of endogenous proteases and phenol oxidase(PPO) in the shrimp,and use the denaturing gradient gel electrophoresis(DGGE) fingerprinting to detect changes of intestinal microflora under these three stresses.Mechanisms of these three stresses on endogenous preservation have been discussed preliminary.1.Shrimps have been under starvation stresses( 0 (control group), 2, 4, 6 d), and frozen to death then store at 4?, the sensory score of starvation group showed significant differences (p<0.05) compared with the control group; The TVB-N value of starvation 4d experimental group reached 25 mg/100g (the first level of freshness) at the forth day(control, 2nd d), reached 30 mg/100g (secondary level of freshness) at the fifth day (control,4th d); and the total number of bacteria of starvation 4 d group was close to the first level freshness limit 5.0 lg(CFU/g) at the forth day (control, 3rd d). Comprehensive analysis, the starvation 4 d group extend the shelf life of shrimp for 1.5 d compared with the control group. The endogenous protease activities of shrimps showed the first fall after rising trend with starvation time lasting, the 4 d group reaches a minimum, with reducing shrimp endogenous protease activity of approximately 41.2%, and rise at starvation 6 d group. The changes on PPO activities of starvation stresses have no significant difference (p>0.05).DGGE fingerprinting show that the optical density values of 6 bands gradually decreased with increasing starvation time, this means the number of these 6 categories intestinal microflora decreased gradually with prolonged starvation time. So starvation can be used to endogenous fresh, The mechanism of it, on the one hand is inhibiting endogenous proteases activities, on the other hand is to reduce the number of microorganisms in the endogenous preservation of shrimp, which physiological activities cause the shrimp's corruption.2.Shrimps were feed with different concentrations of antimicrobial peptides APNT-6 supplemented ( 0 mg/kg (AO), 50 mg/kg (Al), 100 mg/kg (A2), 150 mg/kg (A3), 200 mg/kg (A4) ) for 3 days then frozen to death and stored at 4?. The sensory score of starvation group showed significant differences (p<0.05) compared with the control group;The TVB-N value of A3 group reached 30 mg/100g (secondary level of freshness) at the sixth day (control, 4thd); and the total number of bacteria of A3 group close to the end of shelf life limit 6.0 lg(CFU/g) at the sixth day (control, 4th d). Comprehensive analysis,compared with the control group, the A3 group extend the shelf life of shrimp for 2 d.Endogenous protease activity have a certain amount promotion with antimicrobial peptides APNT-6 in the experimental group, which improved the shrimp endogenous protease activity of approximately 11.7%, while there is no significant difference between the experimental groups; PPO activities gradually increased with enhancing of concentra- tions of antimicrobial peptides , A3 group reaches a certain limit, with improving PPO activity about 0.55 times. DGGE fingerprinting shown that 7 bands are reduced in the experimental group compared with the control group, that means APNT-6 inhibits 7 kinds of the intestinal microbial species. So antimicrobial peptides APNT-6 can be used to endogenous preservation of shrimp, The mechanism of it is inhibiting the number of microorganisms in the endogenous preservation of shrimp, which physiological activities cause the shrimp's corruption.3.Different calcium concentration (191 mg/L(1/2C group ), 382 mg/L(control group,1C group ), 746 mg/L(2C group ), 1529 mg/L(4C group), 3056 mg/L (8C group)) stresses in aquatic environments for 3 days then frozen to death and stored at 4?. The sensory scores of 1/2C, 1C, 2C, and 4C group are close to 6 points that be considered inedible limits at the 2nd d, and 8C group at 3rdd; TVB-N value of 8C group reaches 25 mg/100g(the first level of freshness) at the third day (control, 2nd d) , reaches 30 mg/100g(secondary level of freshness) at the forth day (control, 3rd d); There are no significant differences between 1/2C, 1C, 2C, 4C group in changes in the total number of bacteria,while 8C increased more slowly compared to other groups, the total number of bacteria of 8C group reaches the end of shelf life 6.0 lg (CFU/g) at the fifth day (control, 4th d).Comprehensive analysis , there are no difference in fresh indicators during refrigerated storage between 1/2C, 1C, 2C, 4C group, compared to the control group, 8C group extend the shelf life of shrimp for 1d.The endogenous proteases, phenol oxidase activity increased gradually with increasing of calcium concentration, compared with the control group, 8C group improved protease activity about approximately 72.1%, about 0.4 times of PPO activity. DGGE fingerprinting shows that 8C group displayed a significant reduction in the number of bands, less 5 bands than control group's. Comprehensive analysis , 8C group extend the shelf life of shrimp for 1d, one of its preservation mechanism may be that high concentration of calcium ions can inhibite the microbial physical activity, which caused spoilage of shrimp.