Study On The Changes Of The Quality Of White Shrimp(Penaeus Vannamei) During Storage

In this paper,extraction and characteristics of polyphenol oxidase from white shrimp(Penaeus vannamei)was mainly research.On the basis of this,the quality preservation of P.vannamei during storage was studied.The effects of cooking and storage on the volatile components of P.vannamei were studied.Study on the flavor quality of P.vannamei by cooked and stored;Study on the quality changes of shrimp production of P.vannamei stored at different temperatures.1 The extracted optimization and biological characteristics of polyphenol oxidase(PPO)of white shrimp(Penaeus vannamei)were studied.Firstly,the extraction of PPO from P.vannamei as a function of three experimental parameters including liquid ratio,p H and extraction time were examined with single factor experiment.Then,based on single factor test results,taking optimization of extraction used Response Surface Analysis Method.The extracted enzyme was characterized.The highest PPO activity was obtained after 3 h of extraction with 2:1 liquid ratio at p H 8.0,and which was 94.8 U.It could be used to predict the effect.Kinetic study obeyed the Michaelis-Mentent equation.The Km and Vmax were calculated to be 30.322 mmol/L and 0.281 A/min,respectively.2 To investigate the effects of cooked and stored on the volatile compounds of white shrimp(Penaeus vannamei),the electronic nose(e-nose)and headspace solid phase micro-extraction gas chromatography-mass spectrometry(HS-SPME-GC-MS)were used to analyze the volatile compounds in shrimp meat.The relative odor activity value(ROAV)and sensory evaluation methods were used to evaluate flavor change of shrimp meat.The results of E-nose showed that the effects of cooked and stored treatments were highly remarkable on the volatile compounds of white shrimp.According to GC-MS analysis,50,63,68,49,and 41 volatile compounds were detected in shrimp meat with raw shrimp,cooked shrimp,cooked shrimp cooling,cooked shrimp for placing at 4 ? overnight,and second cooked shrimp,respectively.After the secondly cooked,the key flavor substances were slightly weakened and fresh aroma also decreased slightly in the shrimp meat.However,the first cooked had little effect on shrimp flavor.The raw shrimp meat had been detected nonanal and decanal,which had a significant impact on flavor.Cooked shrimp had been detected nonanal,decanal,tetradecanal and others.The secondly cooked shrimp meat had been detected octadecanal,and butylated hydroxytoluene,which had a greater impact on flavor.The detected types and contents of volatile compounds were reduced in the cooked shrimp after storing,but the total difference was not significant.The results showed that the types and contents of volatile compounds of the second cooked shrimp could be significantly increased,and the key flavor species and contents of P.vannamei were also significantly lower than those first cooked shrimp.The flavor difference of cooked shrimp was not significant at 4 ? for 12 h storage.3 The effects of different cooking on the flavor quality of white shrimp(P.vannamei)were investigated by using electronic nose(e-nose)and electronic tongue(e-tongue)combining with the taste activity value(TAV)and the equivalent umami concentration(EUC).The taste components,flavor nucleotides and free amino acids were determined by Amino acid analyzer and high performance liquid chromatography(HPLC).The results showed that e-tongue and e-nose can effectively distinguish 4 kinds meat of different cooked shrimps(shrimp meat with raw shrimp,cooked shrimp,cooked shrimp for placing at 4 ? for 12 h,and cooked for the second time after storing).Compared with raw shrimp meat,the contents of IMP and AMP decreased in cooked shrimp meat.The contents of ATP,ADP,IMP and AMP in the secondary cooked shrimp meat were significantly increased,in comparison with the cooked shrimp meat.And the contents of flavor nucleotide in the shrimp meat treated with placing at 4 degree centigrade for 12 h was significantly higher(p<0.05).The total amounts of fresh sweet amino acids in raw shrimp and cooked shrimp were relatively high,while the total amounts of bitter amino acids and free amino acids were reduced;And the EUC of second cooked shrimp meat treatment group was lower by about 1 times as compared to the meat of cooked shrimp.However,there was no significant difference in the TAV value of shrimp treated by firstly and secondly cooked treatments.4 In this paper,the effects of different water holding agents on the thawing loss rate,color difference,texture and thiobi thiobarbituric acid(TBA)of frozen shrimp were studied during storage with different temperatures(-20,-50,-80 ?).The results showed that no phosphorus water holding agent group(Sodium citrate 1 %,sodium alginate 0.5 %,sodium chloride 2 %)and composite phosphate group(3 %)could effectively delay the increase of thawing loss rate and a* value of single-frozen shrimp,and had some control effect on ice dry consumption.The thawing loss rate and TBA value of single shrimp under the conditions of-20 ? and-80 ? were significantly different(p<0.05).During the storage process,the no phosphorus water holding agent group and composite phosphate group could significantly retard the decrease of the hardness of shrimp comparing with the control group(distilled water).TBA value can reflect the degree of fat oxidation of aquatic products,the no phosphorus water holding agent group and composite phosphate group can effectively slow down the oxidation.Compared with the control group,chitosan and vitamin C can significantly reduce the quality of shrimp during storage decline,while the vitamin C better.