冻结方式对不同部位草鱼呈味物质的影响

以草鱼腹肉、背肉和红肉为研究对象，采用－40?℃速冻、－20?℃乙醇液体冻结和－20?℃静止空气冻结对草鱼进行冻结处理，采用高效液相色谱法、氨基酸自动分析法以及电子舌测定不同冻结方式的鱼肉中呈味物质含量变化，并测定各部位鱼肉的乳酸含量。结果表明，冻结方式对鱼肉的鲜度和呈味物质含量有一定影响。肌苷酸（inosine monphosphate，IMP）和一磷酸腺苷（adenosine monophosphate，AMP）含量、游离氨基酸总量与冻结速率呈正相关，但乳酸、次黄嘌呤核苷（insoine，HxR）和次黄嘌呤（hypoxanthine，Hx）的含量与冻结速率呈负相关，在－20?℃冻藏条件下贮藏3?d后，－40?℃速冻组K值最小，－20?℃静止空气冻结组K值最大。红肉部分IMP、AMP含量低，而HxR和Hx含量较高，其滋味和鲜度较差，3?种冻结方式中红肉的K值分别为28.99%、40.92%、46.58%；腹肉与背肉中游离氨基酸含量相近，且高于红肉部位，但红肉中天冬氨酸、谷氨酸含量明显高于腹肉和背肉；红肉中乳酸含量显著高于腹背肉，且不同冻结方式对其影响较大。电子舌能有效区分不同冻结方式和不同部位的草鱼肉。

Effect of Freezing Methods on the Taste Components in Different Parts of Grass Carp Meat

The contents of taste components in the belly, dorsal meat and red meat of grass carp frozen by different methods: quick freezing at ?40 ℃, liquid alcohol freezing at ?20 ℃, and static air freezing at ?20 ℃ were determined and compared by high performance liquid chromatography (HPLC), amino acid auto-analyzer and electronic tongue. The lactic acid content of fish meat was also determined. The results were obtained as follows. The freezing methods had an influence on fish freshness and taste components. The freezing rate was positively correlated with the contents of inosine monphosphate (IMP), adenosine monophosphate (AMP) and total free amino acids, whereas it was inversely correlated with lactic acid, insoine (HxR) and hypoxanthine (Hx). Fish samples frozen by the first and third freezing methods showed the lowest and highest K values (freshness index) after 3 d of frozen storage at ?20 ℃, respectively. Of the three meats, red meat contained the highest contents of IMP and AMP but lowest contents HxR and Hx, which led to poor taste and freshness. The K values of red meat frozen by three freezing methods were 28.99%, 40.92%, and 46.58%, respectively. The contents of free amino acids in belly meat were similar to those of dorsal meat, but higher than those of red meat. Notably, red meat was significantly richer in asparagic acid and glutamate as well as lactic acid than belly meat and dorsal meat, and the lactic acid content of red meat was greatly affected by the freezing methods. The different parts of fish meat and fish samples frozen by the different freezing methods were clearly distinguished with an electronic tongue.