Effect Of Antifreeze And Freezing Methods On Quality Of Frozen Cooked Crawfish Tail Meat

Crawfish（Procambarus clarkii）in China is an important freshwater economic aquatic species with a rich yield and high nutritional value.At present,there are a variety of processed crawfish products on the market,such as quick-frozen whole crawfish,flavored leisure shrimp,frozen cooked crawfish tail meat/tail,etc.Among them,frozen cooked crawfish tail meat is one of the important export crawfish products,but the formation and growth of ice crystal in crawfish tail meat during transportation and storage lead to poor sensory quality such as elasticity and chewiness of crawfish tail meat.At present,adding antifreeze agent or using fast freezing method is the most common means to delay the deterioration of aquatic products in the frozen storage process,but there is no further report about the quality change of crawfish tail meat in the frozen storage process from the aspects of the processing adaptability of raw material and synergistic freezing method of antifreeze agents.Therefore,crawfish tail meat was used as an object in this subject to study the processing adaptability of crawfish with different sizes under different cooking time.Furthermore,the ratios of three characteristic antifreeze agents,compound phosphate,trehalose and sorbitol,were optimized and the effects of different antifreeze agents on water distribution and microstructure of crawfish tail meat s during freeze-thaw process were investigated.On this basis,the synergistic effect of antifreeze agent and freezing method on quality maintenance of crawfish tail meat during frozen storage was studied.This study would provide technical references for the preparation and process optimization of high-quality frozen cooked crawfish tail meat.The main research contents and results were as following:（1）The effects of raw material specifications and cooking time on crawfish tail meat quality were studied.The optimal raw material sizes and cooking time were optimized by measuring the cooking rate,centrifugal holding capacity,water content,texture characteristics,color difference and sensory score of crawfish tail meat after cooking.The results showed that the smaller the size of crawfish,the higher the yield of cooking products.But compared with the crawfish of 10-19 g,the crawfish of 20-39 g had better texture characteristics and sensory score.The hardness,chewiness,elasticity and sensory score of20-29 g crawfish were 578.26 g,247.84,0.824 and 8.84,respectively,which were not significantly different from those of 30-39 g crawfish.The yield of cooking products of 20-29 g crawfish was 22.44%,which was significantly higher than that of 30-39 g crawfish（16.77%）（p<0.05）.But there was no significant difference with 10-19 g crawfish（23.71%）.The hardness,chewiness,elasticity and sensory scores of 20-29 g crawfish cooked for 4min were 572.71 g,253.27,0.828 and 8.84,respectively,which were better than those cooked for 3 min and 6 min,but had no significant difference with those cooked for 5 min.The results above indicated that the optimal raw material specifications and cooking time were 20-29 g crawfish and 4 min cooking,respectively.（2）The antifreezing effects of different proportions of compound phosphate,trehalose and sorbitol on crawfish tail meat were compared.Single factor test and orthogonal test were used to determine the thawing loss rate,water content,water retention capacity,content of salt-soluble protein,total sulfhydryl group and texture characteristics of crawfish tail meat,so as to optimize the appropriate proportion of antifreeze agents.In addition,the effects of different antifreeze agents on water distribution and microstructure of crawfish tail meat during freeze-thaw process were investigated.The results showed that more than0.5%compound phosphate,more than 6%trehalose or more than 6%sorbitol had better antifreezing effect in single factor test.Orthogonal experiment results showed that the compound antifreeze agent group（1%compound phosphate+6%trehalose+6%sorbitol）had the best antifreeze effect,and the thawing loss rate was 9.97%,which was significantly lower than that of the single antifreeze agent group（15.95%,17.44%,16.78%）.During freeze-thaw process,the ratio of low field NMR signal intensity over peak area(P₂₂)of crawfish tail meats in each treatment group was decreased gradually,but the signal intensity of the compound antifreeze agent group was changed slightly,and P₂₂ was not significantly changed.The results of scanning electron microscopy and tissue section showed that the microstructure of freezing-thawing combined with antifreeze agent was closest to that of fresh crawfish tail meat.In conclusion,compound antifreeze agent group（1%compound phosphate+6%trehalose+6%sorbitol）could effectively improve the antifreeze ability of frozen cooked crawfish tail meat.（3）The effect of freezing methods and antifreeze agent on the quality of crawfish tail meat was studied.Based on the optimal formulation of compound antifreeze agent,the effects of liquid nitrogen freezing,air blast freezing and refrigerator freezing on the freshness index,physicochemical index,texture characteristics and sensory score of crawfish tail meat during freezing storage were determined.The results showed that p H,TBA,TVB-N values and carbonyl content in each group increased gradually with the extension of frozen storage time,but the increase rate was slow in liquid nitrogen freezing group.After 10 weeks of freezing storage,the TBA,TVB-N values and carbonyl content of the antifreeze combined with liquid nitrogen freezing group were 0.29 mg/kg,3.20mg/kg and 1.24 nmol/mg,respectively,and the increase amplitude was significantly lower than that of the refrigerator freezing group,air blast freezing group and liquid nitrogen freezing group.During frozen storage,water retention capacity,texture properties,salt soluble protein content,total sulfhydryl group content and sensory score showed a decreasing trend,and the decrease was the slowest in liquid nitrogen freezing group.After10 weeks of freezing,the water retention,elasticity and salt-soluble protein contents in the antifreeze combined with liquid nitrogen freezing group were 73.86%,0.755 and 19.01mg/g,respectively,which were lower than those in the control group.In conclusion,among the three freezing methods,liquid nitrogen freezing in coordination with antifreeze agent could effectively maintain the quality of crawfish during frozen storage.