Rapid And Non-invasive Technology To Evaluate The Oyster Freshness

Oyster is one of the most popular seafood products with a high nutritive value,quality protein,variety of amino acids and other physiologically active components.When an oyster is shucked,death ultimately occurs,innate body defences cease and tissue decomposition is initiated via metabolic activities of microbial organisms as well as through biochemical reactions such as oxidation and autolytic enzyme activity.The spoiled oyster would lead to some potential health risks for consumers.Thus,freshness is one of the main quality characteristics for evaluation of oyster safety.Biogenic amines are degradation products generated through enzymatic and microbial processes during food spoilage,which may pose a health hazard to consumers at elevated levels.Therefore,a rapid detection method for biogenic amines is urgently needed.Trimethylamine(TMA)is a good target for the detection of biogenic amines due to its volatility and fishy odor.In this study,we developed a stand-alone dopant-assisted positive photo ionization ion mobility spectrometry(DAPP-IMS)for rapid and sensitive detection of TMA.Response of TMA was enhanced by the addition of dopants and characteristic product ions with reduced mobility 2.26 cm2V-1s-1 were formed.2-Butaone was chosen as the optimal dopant for better separation between reactant ion peak and product ion peak of TMA as well as higher sensitivity,and the limits of detection(LODs)for TMA standard sample was 1 ppbv.The potential application of DAAP-IMS was evaluated by the detection of TMA generated during oyster and shrimp storage.Analysis of two kinds of seafood showed the same characteristic peak to TMA standard sample,and the intensity of TMA increased over the storage time.The results of this study testify to the potential of DAPP-IMS for qualitative and quantitative analytical determination of TMA in real food samples.Besides the generation of TMA,the change of moisture migration and distribution is also occurred during the process of decomposition.In this study,LF-NMR technology was used to monitor the moisture distribution and migration in oyster during storage(25 ?,4 ?,-18 ?).The physical and chemical indicators of oysters(volatile base nitrogen,color,sensory)data were obtained during the process of storage.As shown in the result:The four states of water was named as strong bound water(T2b),bound water(T23),immobilized water(T22)and free water(T21).Conditions and the result reveal that LF-NMR monitoring oyster which storage at-18 ? was not ideal Pearson method and partial least squares regression(PLSR)were used to analysis the correlation between freshness index and NMR data in the process of oyster storage(25 ?,4 ?)respectively:high correlation coefficient(-0.87 ? r?-0.83,0.85? r? 0.95)were obtained between transverse relaxation time(T22,T23)and TVB-N,L*,Whiteness by Pearson;The correlation analysis between T2 relaxation data and the physical and chemical indexes by partial least squares(PLSR),the root mean square error of validation(RMSEC)were less than 2.9.The correlation coefficient(Rc)were greater than 0.94.The prediction for volatile base nitrogen,whiteness and brightness was ideal based on T2 relaxation data of LF-NMR.The results indicated that the novel method based on LF-NMR technology provide a potential application to evaluate the freshness of oyster.