| The tiger frog (Hoplobatrachus rugulosus) is one of the important economic frogs in China. It is highly appreciated by people because of its unique pleasant aroma, delicious taste and high nutritional value. However, owning to the destruction of habitat and overhunting, the number of wild tiger frog is getting smaller and smaller. It has been listed as the Class II national protected species in China. In order to alleviate the contradiction between the protection and consumption, captive breeding of tiger frog has been carried out widespread. But, until now there is no breeding research reported on tiger frog. In this research, wild tiger frog harvested at four different regions of China:Jinhua in Zhejiang, Xuancheng in Anhui, Yiyang in Jiangxi and Jian'ou in Fujian, were subjected to common nutrition indexes (proximate composition, hydrolytic amino acids, fatty acids and minerals), free amino acids (FAA) and volatile flavor compounds analyses. And nutritional quality and flavor quality of tiger frog from different regions were systematically evaluated and compared, in order to provide the theory basis for the better utilization and development of tiger frog germplasm resource and promote the healthy development of the aquaculture of tiger frog. Main research results are as follows:1. A comparative study on nutritional quality of tiger frog from different regionsAfter comparing the nutritional quality of tiger frog from different regions, we found, the meat yield was higher (37.01%-45.29%) and of no significant different (p>0.05) among the four regions. Jinhua tiger frog had the highest of protein and fat contents (21.82 g/100g and 0.67 g/100g), but there existed some degree of difference compared with others. Yiyang tiger frog had the lowest protein and fat contents (19.19 g/100g and 0.50 g/100g), and was no significant difference (p>0.05) from Jian'ou tiger frog. Jinhua tiger frog had the highest content (21.07 mg/100g) of total hydrolytic amino acids (TAA), but there existed some degree of difference compared with others. Yiyang tiger frog had the lowest content of TAA (17.66 mg/100g), and was no significant difference (p>0.05) from Jian'ou tiger frog. The essential amino acid (EAA) contents of Jinhua and Xuancheng tiger frog were also no significant difference (p>0.05), and higher than that of others regions. The EAA contents of Yiyang and Jian'ou tiger frog were also no significant difference (p> 0.05). However, there existed limiting amino acid in Jinhua and Xuancheng tiger frog. Yiyang and Jian'ou tiger frog had well-balanced EAA compositions. Xuancheng tiger frog had higher contents of glutamic acid (Glu), aspartic acid (Asp), leucine (Leu), lysine (Lys), isoleucine (Ile) and valine (Val).The fatty acids of tiger frog meat was dominated by unsaturated fatty acid (UFA) (66.59%-69.28% of the total fatty acids). Jinhua tiger frog had the highest UFA content, but there existed some degree of difference compared with others. Yiyang tiger frog had the lowest UFA content, and was no significant difference (p>0.05) from Jian'ou tiger frog. The contents of monounsaturated fatty acid (MUFA) of Jinhua and Xuancheng tiger frog were higher than that of polyunsaturated fatty acid (PUFA). The contents of PUFA of Yiyang and Jian'ou tiger frog were higher than that of MUFA. The highest content of PUFA was found in Jian'ou tiger frog which had higher contents of arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosaheraenoic acid (DHA). For n-6/n-3PUFA, tiger frog meat was an n-3 PUFA rich food in usual diet. Jinhua tiger frog had higher the ratio of n-3/n-6 and maybe higher nutritional value.The tiger frog meat contained rich minerals. Cu is one of the important minerals of tiger frog meat. Xuancheng tiger frog had higher levels of Cu, Fe and Zn, and the nutritive value of it was superior to that of others.2. A comparative study on flavor quality of tiger frog from different regions Jinhua tiger frog had the lowest content of total FAA (1559.13 mg/100g), and Yiyang tiger frog had the highest content of total FAA (2364.78 mg/100g). Taurine (Tau) was the major FAA of tiger frog meat and taken 18.03%-44.39% of total FAA content. Jinhua tiger frog had the highest content of Tau (692.07 mg/100g), and was no significant difference (p> 0.05) from Xuancheng tiger frog. Yiyang tiger frog had the lowest content of Tau (426.33 mg/100g), and was no significant difference (p> 0.05) from Jian'ou tiger frog. Umami amino acid Asp and Glu were the main taste-active amino acids. According to the taste activity values (TAVs) of these two amino acids, the umami taste of Jinhua tiger frog was more intense, while that of Yiyang tiger frog was more weaker, when compared with those of others.Volatile flavour compounds of tiger frog meat extracted by headspace-solid phase microextraction (HS-SPME) were analyzed by gas chromatography-mass spectrometry (GC-MS). By analyzing and comparing the qualitative and quantitative results of volatile flavour compounds of tiger frog from different regions, we found, the content and composition of volatile flavour compounds of tiger frog existed some differences among different regions. Principal component analysis (PCA) was performed to further identify difference of volatile compounds of tiger frog from different regions, and the result showed that Jinhua area was separated from other areas. By analyzing potential contribution on the overall flavor of different volatile flavour compounds of tiger frog and combining the method of "relative odor activity value" (ROAV), we found, the key odor compounds of tiger frog from different areas were different, and flavor characteristics were also different to some extent, however, tiger frog from different areas had essential consistent meat aroma and differences of flavor intensity were shown. Overall, Jinhua tiger frog was superior to others, while the flavor of Yiyang tiger frog was lighter.
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