Association Studies Between Muscle Degradation And Flavor Variation Of Grass Carp During Storage

Grass carp, Ctenopharyngodon idellus, is of largest aquaculture production of freshwater fish in China. Because of its tenderness, nutritiousness and moderate price,grass carp is favored by the majority of consumers. But it can be easily spoiled during storage, transportation and processing. Flavors and qualities are regarded as important indicators of fish products. Lipid peroxidation and protein degradation are the main causes of the flavor change in fish products. Therefore, it is important to conduct in-depth research to investigate the relationship between lipid, protein degradation and flavor change of grass carp muscle during storage. It is hopeful to provide a theoretical basis for the improvement and stability of its product flavor.In the present study, dynamics of lipid peroxidation, protein degradation and flavor variations were investigated for grass carp muscles stored at 25?( room temperature, RT) and 4?(Low temperature, LT) separately. Lipid peroxidation caused indices such as total fat, acid value(AV), thiobarbituric acid value(TBARS), total fatty acid(TFA), free fatty acid(FFA) and phospholipids, as well as protein degradation related indices such as non-protein nitrogen(NPN) and free amino acid(FAA) were studied. Electronic nose, electronic tongue, and solid phase microextraction(SPME)-gas chromatography-mass spectrometer(GC-MS) were combinedly used to trace the flavor change of grass carp muscle each certain time point to clarify the relationship between lipid and protein degradation and flavor deterioration of grass carp muscle. Building a new theoretical guidance to corruption mechanism based on the studies. The concrete findings are as follows:(1)With the extension of storage time, the crude fat contents of grass carp muscle declined, while AV and TBARS values rose. TBARS values declined rapidly after 12 th day of LT and 12 th hour of RM, it can be speculated that these were the two important time points of freshness change of grass carp muscle during preservation.(2)As to TFA, at the 15 th day of LT, monounsaturated fatty acid(MUFA)and polyunsaturated fatty acid(PUFA)decreased by 10.62% and 26.96%, while at the 24 th hour of RT, MUFA and PUFA decreased by 11.64% and 46.18%, respectively. For FFA, at the 15 th day of LT and 24 th hour of RT, PUFA decreased by 32.96% and 52.23%, linoleic acid by 19.03% and 46.29%, and arachidonic acid by 14.25% and 82.51%, respectively. Phospholipids contents were also declined with the extension of storage.(3)During storage at RT, the NPN content variations of grass carp muscle took on the trend increased firstly, and then declined, finally increased again. Stored at LT, NPN content increased first and then declined. FAA content was generally higher in back muscles than in abdominal muscles. The characteristic FAA were mainly composed of taurine, histidine, glycine, lysine and alanine. The amplitude of variation of FAA content stored at RT was wider than that stored at LT. Most of the detected FAA was those displaying sweet, sour, umami and bitter.(4)Compared with LT, grass carp muscle stored at RT produced characteristic smell of corruption more quickly, and corrupted more rapidly. Results found that nitrogen oxides, amines and aliphatic aromatic substances representative sensors response intense with the extension of preservation time. Nitrogen oxides representative sensor responded more obvious at the 12 th day of LT. For the later two substances, sensors response more obvious after stored at the 12 th hour of RT, and can be used as an important basis for grass carp muscle freshness detection. PCA analysis showed that the 12 th day of LT and the 12 th hour of RT were two important points of freshness changes of grass carp muscle. Results found that acerbity, bitter and umami played a dominant role in different storage time, variation trend of each taste components was broadly in line with the FAA. PCA found that the main difference of taste in abdominal muscles at different storage periods was bitterness, but that was umami in back muscles. Compared to abdominal muscles, back muscles had a stronger sense of taste, and relative to LT, taste index changes more obvious than at RT.(5)Correlation analysis found that there were significant correlations between peroxidation dynamics of linoleic acid and oleic acid and 1-hexanol content(y=1.787x-16.857 R~2=0.530, and y=2.410x-93.424 R~2=0.852). The peroxidation dynamics of oleic acid also had a significant correlation to 1-octene-3-ol(y=1.535x-46.149 R~2=0.411). Linoleic acid had a significant correlation to ethanol sensor, methane sensor and chloral hydrate-sulfur sensor(y=-5.237x+87.318 R~2=0.912, and y=-4.070x+68.035 R~2=0.931, and y=-2.876x+48.579 R~2=0.803). Oleic acid had a significant correlation with aliphatic-methane sensor(y=-0.353x+17.730 R~2=0.929). And histidine had a significant correlation with umami(y=1.963x-10.764 R~2=0.801). These sensors could be used as the important indices for freshness evaluation.The present study had analyzed the relationships between lipid peroxidation, protein degradation and the flavor change of grass carp muscle during preservation systemly, and had established the correlation models. These findings would provide a theoretical basis for the rapid detection of the freshness of freshwater fish, and mechanisms of antisepsis and flavor generation.