Studies On The Quality Changes Of Red Swamp Crayfish And Its Specific Spoilage Organisms During Low Temperature Storage

Red swamp crayfish(Procambarus clarkii)is highly popular among consumers because of its unique flavor and nutritive value when well cooked.However,crayfish is a kind of seasonally strong aquatic product.The purpose of this study was to seek suitable methods which can prolong the shelflife of crayfish and solve the problem of tight supply and high price in its off-season.This paper compared the effect different frozen methods,storage temperature on its freshness quality and researched the specific spoilage organisms and the quality changes of red swamp crayfish during low temperature storage,indentifing its SSOs during cold storage.This study aims at finding out the internal cause of quality change in crayfish meat,providing the theoretical theory to maintain freshness quality during its cold chain transport,storage,processing.The mian results were as follows:(1)To improve the quality of the red swamp crayfish,the crayfish samples were frozen by the liquid nitrogen frozen,individual quick frozen and refrigerator frozen respectively and were stored at-18 ?.The effect of different frozen methods on the quality of crayfish during frozen periods was investigated by physiochemical indexes,such as TBA,TVB-N,texture,AG and NAG activity.The SDS-PAGE and scanning electron microscopy(SEM)were also used to compare the freezing effect.The results showed that TBA and TVB-N values of red swamp crayfish increased with the storage time,but showing a relatively slow tendency in the samples treated by liquid nitrogen frozen.After 180 days storage,the TBA values treated by three freezing methods(refrigerator,individual quick,liquid nitrogen)reached 1.05,0.89,0.74 MDA mg/kg respectively.And the TVB-N values reached 30.33,25.48,23.43 mg/100 g respectively,which suggests that liquid nitrogen frozen could effectively keep fresh of red swamp crayfish.In addition,texture values and SEM profiles also proved red swamp crayfish had better quality with liquid nitrogen frozen.(2)To improve the quality of the red swamp crayfish,the crayfish samples frozen by the liquid nitrogen were stored at-18 ?,-40 ?,-60 ? respectively.The effect of different storage temperatures on the quality of crayfish during frozen periods was investigated by physiochemical indexes,such as TBA,TVB-N,texture,AG and NAG activity.The SDS-PAGE and scanning electron microscopy(SEM)were also used to compare the effect.The results showed that TBA and TVB-N values of red swamp crayfish increased with the storage time,but showing a relatively slow tendency in the samples treated at-60 ?.After 180 days storage,the TBA values treated by three storage temperatures(-18 ?,-40 ?,-60 ?,)reached 0.74,0.54,0.51 MDA mg/kg respectively.And the TVB-N values reached 23.43,10.83,8.21 mg/100 g respectively,which suggests that low temperature freezing storage could effectively keep fresh of red swamp crayfish.In addition,texture values,SDS-PAGE patterns and SEM profiles also proved red swamp crayfish had better quality at-60 ?.(3)The changes of volatile compounds of raw and cooked crayfish during frozen storage were analysed by SPME-GC-MS.The influence of different storage temperature on volatile compounds of crayfish were also investigated.The volatile compounds of them were mainly composed of aldehydes,esters,ketones,aromatics,amine,nitrogenous compounds and hydrocarbons.The content of aldehydes,esters and hydrocarbons were gradually decreased during storage,while ketones,aromatics,amine,nitrogenous compounds which caused unpleasant flavor of crayfish were showed opposite trend.The results revealed that-60 ? could effectively maintain the original volatile compounds and fresh quality of crayfish.(4)In order to reveal the microbial diversity and specific spoilage organisms(SSOs)of red swamp crayfish under 4 ? refrigerated condition,the SSOs were individually isolated using the culture dependent method in this study.And their spoilage ability was analyzed to ensure its SSOs.Meanwhile,high-throughput sequencing technology was also used to identify the bacterial species of the red swamp crayfish during its freshness,the middle and the end of corruption period,which researched the changing trend of microbial community during storage at 4 ? and compared the differences between these two methods.The results showed that there were 11 strains of SSOs by culture medium,and Aeromonas jandaei had the strongest spoilage ability while Citrobacter freundii had the weakest one.In addition,high-throughput sequencing methods revealed Shewanella spp.,Carnobacterium spp.,Brochothrix spp.,Psychrobacter spp.,Vagococcus spp.and Acinetobacter spp.shared a total of 90.57%species abundance during the end of corruption.Comparing this two methods,the results showed that the SSOs in chilled crayfish mainly include Shewanella spp,Carnobacterium spp.,Brochothrix spp.,Psychrobacter spp.,Vagococcus spp.,Acinetobacter spp.,Aeromonas jandaei,Trichococcus spp.,and so on.