Identification Of Specific Spoilage Organisms And Their Effects On The Physiochemical Properties Of Little Yellow Croaker

As one of the four most famous commercial seafood in East China Sea,little yellow croaker(Larimichthys polyactis)are popular with customers due to their freshy and tender fish meat.However,the fish are easily spoiled due to microorganism activities,and the relevant research on specific spoilage organisms(SSOs)is rather rare.Therefore this study focused on the SSOs of refrigerated little yellow croaker in different packing conditions as well as their effects on the physiochemical properties,as a basic fundermental for further specific inhibition of SSOs.Sensory evaluation showed that the shelf-lives of refrigerated little yellow croaker in air,vacuum packing(VP)and modified atmosphere packing(MAP)conditions were 4 days,6 days and 10 days respectively.Culture-dependent and culture-independent methods were applied to identifiy the SSOs from refrigerated little yellow croaker at the end of shelf-lives.Results showed the SSOs of refrigerated little yellow croaker stored in air were Shewanella glacialipiscicola,Proteus hauseri,Providencia heimbachae and Planococcus,while Aeromonas salmonicida,Carnobacterium maltaromaticum,P.hauseri and S.glacialipiscicola in VP and Carnobacterium maltaromaticum and S.glacialipiscicola in MAP.The spoilage potential of SSOs were identified.The sensory evaluation showed the scores of fish cubes inoculated by Planococcus in air and P.hauseri in VP falled relatively slowly.In the second round,chemical spoilage indexes,including Total viable counts(TVC),Total volatile basic nitrogen(TVB-N),Trimethylamine(TMA)and K-values,were measured in every inoculated fish cubes.The results showed that the changes of TVC,TVB-N and TMA values could be well separated in every inoculated samples,while the change of K-values are correlated more with food materials rather than SSOs and packing conditions.Yield factors showed the spoilage potential of S.glacialipiscicola is inferior to P.hauseri but stronger than P.heimbachae in air.The spoilage potential of C.maltaromaticum is inferior to S.glacialipiscicola but stronger than A.salmonicida in VP,and The spoilage potential of C.maltaromaticum is inferior to S.glacialipiscicola in MAP.The new evaluation method showed spoilage potential of S.glacialipiscicola is inferior to P.hauseri but stronger than P.heimbachae in air,while C.maltaromaticum and S.glacialipiscicola were the same in spoilage potential both in VP and MAP.The accurency of TVB-N values applied in the new method was higher than TMA did.The properities of little yellow croaker cubes inoculated by SSOs was measured.SSOs would accelerate the increase of pH values in all conditions,but no significant difference caused by SSOs was found at the same condition.Results of texture analysis showed that S.glacialipiscicola and P.hauseri showed great effect on texture,especially leading to the drastic decrease on hardness and chewiness.VP and MAP themselves would affect the hardness of cubes.A regression analysis showed that significant correlation between sensory scores and texture parameters was found,which means sensory scores can be well predicted by texture parameters,GC-MS showed the numbers and amount of volatile compounds in air ranked first and last in MAP.The species of volatile compounds in one condition were similar among each SSO.The specific spoilage volatile compounds of each SSOs was selected by Principal Component Analysis(PCA),and most of them are nitrogenous and sulfurous compounds,ester,alcohol aldehydes and ketones.Correlation research showed that most of the specific spoilage volatile compounds were extremely significant with TVB-N values on a SSO,suggesting it is alternative for these volatile compounds to evaluate the spoilage potential of SSOs.