| As one of the most important aquaculture products in the world,Litopenaeus vannamei is also the leading species in the shrimp culture industry in China.Fresh shrimp occupies an important share in the aquatic products trading market because of its delicate,elastic taste and high safety.With the continuous expansion of the consumption market of Litopenaeus vannamei and the unique regional distribution of culture in China,the transportation of Litopenaeus vannamei in the fresh e-commerce model is facing severe challenges.it is urgent to further optimize and study more efficient live circulation technology to meet different supply and consumption needs.In this paper,based on the previous warehouse model,the circulation process of Litopenaeus vannamei is divided into “low temperature water transportation + pre-warehouse temporary culture + anhydrous oxygenation transportation",which simulates the complete supply chain system from culture end to consumer end.The main results are as follows:(1)Taking the water transport technology of precooling anesthesia as the main research subject,the effects of pre-cooling temperature(A),pre-cooling time(B)and transport temperature(C)on the survival rate of Litopenaeus vannamei were studied by Box-Bohnken response surface method..The percentage of survival shrimp in each group to the total number of shrimp after resuscitation of 30 min was recorded as the actual transport survival rate.The results showed that pre-cooling temperature and transport temperature could significantly affect the survival rate of low-temperature water transport of Litopenaeus vannamei(p < 0.05),and the transport temperature had a very significant effect on the survival rate(p < 0.01).However,the pre-cooling time had no significant effect on the survival rate after transportation(p > 0.05).After optimization,under the condition that the survival time of Litopenaeus vannamei is 12 h,the best low temperature water transport conditions are as follows: pre-cooling temperature 21.5 ℃,pre-cooling time 8 min,transport temperature 17.4 ℃.(2)The effects of vitamin C(0,100,100 and 200mg/L)on oxidative stress and non-specific immune response of Litopenaeus vannamei were studied by adding different concentrations of vitamin C(0,100,200mg/L)to temporary culture before transportation and low temperature water transportation.The results showed that the addition of vitamin C to the water body during temporary culture and water transport could significantly reduce the degree of oxidative damage of Litopenaeus vannamei,reduce the content of malondialdehyde(Malondialdehyde,MDA),enhance the activity of antioxidant enzymes and antioxidant capacity,and promote the activity of immunerelated enzymes in different degrees.Compared with the high concentration vitamin C group,the low concentration vitamin C group showed lower degree of oxidative damage and higher activities of antioxidant enzymes and related immune enzymes at the stage of post-transport resuscitation.This may make the shrimp in the low concentration vitamin C group better adapt to the environmental changes during the recovery process,and is beneficial to the follow-up culture.(3)The orthogonal test was used to optimize the operation conditions in the simulated post-transport temporary curing and anhydrous oxygenation transportation stages.Among them,the best conditions of 12 h temporary culture of Litopenaeus vannamei after low temperature water transportation for 12 h were as follows: salinity10 ‰,temperature 19 ℃,the ratio of shrimp to water(w/w)was 1:8;the best operating conditions of Litopenaeus vannamei after water transportation for 12 h and anhydrous aerobic transport for 2 h after 12 h temporary culture were as follows: temperature17 ℃,shrimp-air ratio(w/v)1:3,using sawdust as cushion material.In addition,in order to treat nitrogen-containing compounds in temporary culture water,a tubularmoving bed biofloc reactor was constructed and cultured in biofilm for 50 days,and then applied to the temporary culture stage of shrimp.Compared with the temporary tank with only aeration equipment,the temporary tank with tubular-moving bed bioreactor can effectively deal with ammonia nitrogen in water and alleviate the accumulation of nitrate.(4)Based on the results of the three-part optimization experiment,the changes of muscle quality and energy metabolism of Litopenaeus vannamei in the circulation mode of keeping alive in the front warehouse were studied.the experimental results showed that keeping alive circulation could increase the muscle brightness of Litopenaeus vannamei,that is,tend to be transparent,but had no significant effect on the body color brightness of cooked shrimp.Due to the environmental stress in keeping alive circulation,the anaerobic metabolism level of shrimp may be enhanced,resulting in the glycolysis of glycogen and the accumulation of lactic acid in the body,thus affecting the water holding capacity of muscle p H;shrimp muscle will decrease with the extension of circulation time,and the hardness,elasticity and chewiness of texture properties will decrease in varying degrees;muscle shear force fluctuates between stages,and can be restored to the pre-transport level after circulation.In the observation of muscle microstructure,the muscle structure of shrimp was fragmented,and the muscle fiber gap was increasing,and in serious cases,longitudinal cracking and myofibril disorderly appeared. |
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