Effect of ultra low temperature freezing on the shell cracking rate of Portunus trituberculatus

Alive crabs ( Portunus trituberculatus) were pre-treated with different procedures of ultra-low temperature quick freezing by liquid nitrogen, followed by storage at-18 ℃. Proper initial temperature and freezing procedures were screened based on the ratio of shell cracking as the key indicator that important for the industrial application.Sensory evaluation, TVB-N and water holding capacity was investigated for obtaining the optimum quick freezing procedure both the lower crack ratio and the best quality of the swimming carb for further storage.The results showed that the crab had a lower cracking rate of 8.0%, with corresponding sensory scores of 7.5 points, water holding capacity of 69.9% and TVB-N value of 14.62 mg/100 g under the quick freezing procedure of the chamber ambient temperature of the liquid nitrogen quick freezer decreased to-20 ℃ in2 min, further to-40 ℃ in 2 min, then to-80 ℃ in 3 min, and keeping the ambient temperature of-80 ℃ until the central temperature of the sample to be-40 ℃.The swimming carb kept a relatively better quality for storage of 180 d.