Changes Of The Volatile Compounds In Chinese Mitten Crabs(Eriocheir Sinensis) And Its Mechanism During The Frozen Storage

Eriocheir sinensis,also known as crab,is an economic kind of crab.According to the statistics report,the annual output of Chinese mitten crab was over 720,000 tons in 2014,generating huge economic benefits.Chinese mitten crab is well received by consumers because of its unique flavor,but it is a very seasonal food,the annual September,and October is the best time to taste the best crab,in addition to other season,can not taste the best crab,so frozen crab came into being.Frozen crab is the cooked crabs meat and gonad part,packaging and froze storage products,frozen crab can be eated directly afterheating,but also as a seasoning with other food.But with the extension of storage time,the volatile compounds would still be changed,it would have a direct impact on the overall flavor of aquatic products,the smell and fresh samples were significantly different.In this experiment,we used the GC-MS to find the odor substances and their causes in the process of frozen storage.The conclusions were as follows:(1)The edible part of the steamed Eriocheir sinensis is frozen and the sensory and volatile odor substances are measured every 30 days.The results show that at 180 days the gonad part of crab lost its unique fat flavor,oil consumption and smell strong,sensory unacceptable;in 240 days male crab and female crab meat lost its original meat flavor and fresh sweet fades,Strong ammonia and accompanied by soil smell,the senses can not accept.With the extension of storage time,nonal,2,6-nonadienal,2,4-decadienal and other smell,oil consumption of substances in the gonad of crab significantly increased,trimethylamine,1-octen-3-ol in crab meat,which is the main reason for the decrease in the overall sensory evaluation score.(2)The physical and chemical indexes of the edible part of Eriocheir sinensis were recorded after the frozen storage.The results showed that the p H value of the gonad part of crab changed after 180 days of freezing,but no significant fluctuation occurred.The value of TBA was increasing in 30 days and 60 days,and reached the maximum at 180 days.After 240 days of frozen storage,the p H value of crab did not change greatly.TVBN valuescontinue to rise but still within the scope of the national standard;TBA value did not change significantly.It is inferred that when the storage time reaches 180 days,the crab crab paste is still edible,and when the storage time reaches 240 days,the crab is still edible.(3)The contents of free amino acids and fatty acids in the edible parts of Eriocheir sinensis were studied.The results showed that the contents of threonine,serine and alanine were significantly changed with the time of freezing time,and the contents of threonine,serine and alanine were significantly changed.Proline,tyrosine and other five kinds of amino acids in the content of a significant change;and female crab meat glutamate,glycine,isoleucine and other 10 kinds of amino acid content changes significantly.Wherein lysine,phenylalanine,serine and threonine are thought to have synergistic effects on the formation of soil flavor.13 kinds of unsaturated fatty acids were detected in crab crab,and 10 kinds of unsaturated fatty acids were detected in crab meat.With the prolongation of freezing time,the content of monounsaturated fatty acids was not obvious,the degree of oxidative oxidation of crab crabs increased,4 kinds of polyunsaturated fatty acids decreased,crab meat EPA and docosahexaenoic acid content decreased,the other fatty acids basically no change.This is consistent with the trend of TBA values.(4)The correlation analysis of the odor active substances and the indexes of Chinese mitten crabs after freezing found,the main reason for the deterioration of odor after freezing is the decomposition of unsaturated fatty acids and the decomposition of nitrogenous substances.The resulting benzaldehyde and nonanal are the main contributors of the smell.Trimethylamine is the main contributor to ammonia.Octene-3-ol has an important contribution to the smell of soil,2,4-decadienal is the product of linoleic acid oxidation,oil consumption.