Quality changes of yellow grouper(<I>Epinephelus awoara</I>) fillets stored under vacuum packaging at 0 ℃

Abstract

Sensory attributes,total number of bacteria,physical and chemical parameters ( proximate composition,texture analysis,color measurements,pH,TBA,TMA-N,TVB-N,K-value,Ca2 +-ATPase activity, SDS-PAGE) changes of yellow grouper ( Epinephelus awoara) stored under vacuum packaging at 0 ℃ were investigated.The results showed that yellow grouper was a fish with low level of fat but high level of protein.During the storage,sensory attributes( odor and taste) exhibited significant variations and correlations in storage time( r=0.94 and 0.98,respectively) .Taste score increased faster than the odor score,however,neither of them reached the reject limit of 3 scores.There were significant linear increases in total viable counts( TVC) in the storage( r=0.97) .TVC on the 12th day was lower than 4 Log CFU/g,indicating the fillets kept at first grade of freshness,and was 4.34 Log CFU/g at the end of 15 days storage,kept at second grade of freshness.With regards to the texture profile,hardness( r =-0.89) ,gumminess( r =-0.73) ,chewiness( r =-0.87) showed a significant and negative correlation with storage time.L and the chroma values decreased,and b values increased,reflecting the colour changes experienced by the fillets over time.No significant differences were found in pH and TBA concentrations during the storage and they displayed a weak correlation with time, so they may not be the suitable indicators for reflecting the quality changes of yellow grouper fillets during the storage.The amount of TVB-N and TMA-N significantly increased with time,at the final of storage,TVB-N and TMA-N reached 12.94 mg N/100 g and 0.75 mg N/100 g respectively,and both of them were lower than limit.The proteolytic degradation of muscle protein was observed by SDS-PAGE,the results showed that MHC and Actin were hydrolyzed continuously throughout storage.Ca2 +-ATPase activity declined fast from the initial value of 0.25 μg Pi/( min·mg) to the final value of 0.07 μg Pi/( min·mg) .K value increased fast with time ( r =0.98) and reached 54.91% at the end of storage,keeping the middle level of freshness.The results suggested that total viable counts( TVC) increased slowly under vacuum packaging at 0 ℃,and it kept good sensory characters,inhibited the changes of the paraments( TVB-N value,etc.) and hydrolysis of protein.The sensory attributes,microbiological counts,texture( hardness,cohesiveness and chewiness) ,colour( L ,b ,and Cab) ,TVB-N,TMA-N,Ca2 +-APTase activity and K value exhibited strong correlations with storage time and were sensitive.Therefore,they may be considered as good indicators for evaluating yellow grouper spoilage during the storage under vacuum packaging at 0 ℃ for 15 days,but the consideration of shelf-life should be combined with all those indicators.