| Leiocassis longirostris is belong to the siluriformes, bagridae, which is known for its tender and delicious muscle and less intermuscular bone, so there is a proverb called ―if you have not eaten Leiocassis longirostris, that means you have not known fish‖.Its back is black, and abdomen is pale, the whole body is smooth。It widely distributes throughout China’s Yangtze river and major tributaries in China. Due to environmental degradation and the reduction of resources, the number of Leiocassis longirostris sharply reduced. To solve the problem, the Chinese aquaculture researchers has carried out a series of studies on Leiocassis longirostris growth, breeding, reproduction technology, now sichuan, guangdong, guangxi, hunan, hubei, jiangsu and other places have going on artificial breeding technology about Leiocassis longirostris, now there are multiple breeding mode such as ponds, cages, factory and other breeding modes. At present, there are not any integrated public reporting on nutrition, volatile flavor analysis of farmed and wild Leiocassis longirostris. The subject research is to study chemical composition, volatile flavor composition between farmed and wild Leiocassis longirostris, then making a comprehensive evaluation about them. In the end, providing the basic theory for aquaculturing, feed formula, the quality improvement and processing techniques of Leiocassis longirostris.The main conclusions are as follows:1. In order to compare the differences in muscle nutrient composition between cultured and wild Leiocassis longirostris, the nutrient components of muscles between cultured and wild Leiocassis longirostris were analyzed. The general nutrient compositions were determined with routine methods. Amino acid compositions were determined with amino acid analyzer. Fatty acid compositions were inspected with gas chromatograph-mass spectrometry. The results showed that the moisture content in muscle of farmed Leiocassis longirostris was significant higher than that of wild Leiocassis longirostris(P<0.01), while the contents of crude protein and crude fat were significant lower than those of wild Leiocassis longirostris(P<0.01), and no significant difference was found in the content of ash content between farmed and wild Leiocassis longirostri(P>0.05). There were 18 kinds of amino acids found in the muscles of farmed and wild Leiocassis longirostris, the content of total amino acid(TAA)of farmed Leiocassis longirostris was significant higher than that of wild Leiocassis longirostris(P<0.05). No significant difference was found in the content of total essential amino acid(EAA) between farmed and wild Leiocassis longirostris(P>0.05). It was clear that the content of the different amino acids in muscle of farmed and wild Leiocassis longirostris was stable, and the constitutional rate of the essential amino acids met FAO/WHO standards. According to nutrition evaluation in amino acids score(AAS) and chemical score(CS), the first limited amino acid of farmed and wild Leiocassis longirostris was tryptophan. The delicious amino acids(DAA) of farmed Leiocassis longirostris was significant higher than that of wild Leiocassis longirostris(P<0.01). There were 25 and 27 kinds of fatty acids detected in farmed and wild Leiocassis longirostris, respectively,and no significant difference was found in the content of saturated fatty acids(SFA) between farmed and wild Leiocassis longirostri(P>0.05), the content of monounsaturated fatty acids(MUFA) was significant lower than that of wild Leiocassis longirostri(P<0.01), the total content of n-6 polyunsaturated fatty acids(PUFA) was higher than that of wild Leiocassis longirostri(P<0.01), no significant difference was found in the content of n-3 polyunsaturated fatty acids(PUFA) between the muscles of farmed and wild Leiocassis longirostri(P>0.05), while the total content of polyunsaturated fatty acids( PUFA) was significantly higher than that of wild Leiocassis longirostri(P<0.01). No significant differences was found in the index of atherogenicity(IA) and index of thrombogenicity(IT) between farmed and wild Leiocassis longirostri(P>0.05). In conclusion, the nutritional quality of farmed Leiocassis longirostri which were fed formula feed was not decreased by comparison with wild Leiocassis longirostris. We could improve the nutritional quality of farmed Leiocassis longirostris by means of adjusting the feed formula.2. The volatile flavor composition of wild and cultured Leiocassis longirostris muscles were analyzed by simultaneous distillation extraction(SDE) and gas chromatography and mass spectrometry(GC-MS). The results showed that 70, 60 volatile compounds were detected in wild and cultured Leiocassis longirostris muscles, respectively. Among these compounds, most were aldehydes, alcohols, ketones, hydrocarbons, acids and esters. The contents of major volatile compounds were hydrocarbons, aldehydes, alcohols, which accounted for 1555.74 ng/g, 693.46 ng/g, 380.38 ng/g in wild Leiocassis longirostris and 3270.53 ng/g, 348.8 ng/g, 104.11 ng/g in cultured Leiocassis longirostris, respectively. Wild and cultured Leiocassis longirostris both showed fishy, fatty and grassy, and volatile carbonyl compounds and alcohols made a greater contribution to the odor characteristics of wild and farmed Leiocassis longirostris muscles. At the same time, esters, benzene and naphthalenes, which came from feed and water environment, also affected the odour of Leiocassis longirostris meat. According to the results, the fishy smell of wild Leiocassis longirostris muscles was heavy than cultured Leiocassis longirostris.3. The routine biochemical assays were used to evaluate the nutritional composition and quality of cultured Leiocassis longirostris between dorsal and ventral, the results showed that moisture content of the dorsal is higher than ventral of Leiocassis longirostris significantly, the protein, fat and ash are lower than ventral significantly. Amino acids were analyzed in dorsal and ventral of cultured Leiocassis longirostris, including 18 kinds of amino acids totally, 8 kinds of essential amino acid(EAA), 2 kinds of semi-essential amino acids(NEAA), 8 kinds of non-essential amino acids(NEAA), The TAA、EAA of dorsal are higher than ventral,the amino acid composition of dorsal and ventral both completely accords with the standards of the FAO/WHO. The delicious amino acid of dorsal are higher than ventral significantly, which showed that the dorsal of cultured Leiocassis longirostris is more delicious; There are 25, 24 kinds of fatty acids detected in dorsal and ventral of cultured Leiocassis longirostris, saturated fatty acids and n-6 polyunsaturated fatty acids of dorsal are lower than ventral,while monounsaturated fatty acids and n-3 polyunsaturated fatty acids are higher than ventral,and there are extremely significant difference between them.4. The volatile flavor compounds in dorsal and abdominal meat of cultured Leiocassis longirostris were extracted by headspace solid phase microextraction(HS-SPME) and gas chromatography and mass spectrometry(GC-MS). A 65 μm Polydimethylsiloxane/ Divinylbenzene(PDMS/DVB) fibre was selected for HS-SPME. The results showed that 31 volatile flavor compounds were isolated and identified from the dorsal muscles, and 47 compounds were detected from the abdominal muscles, in which 25 compounds including alcohols, adehydes, ketones, hydrocarbons and esters were the same. 1-penten-3-ol, 1-octen-3-ol, pentanal, hexanal, heptanal and nonanal made a great contribution to the flavor of cultured Leiocassis longirostris. According to the comprehensive analysis, the odour of dorsal meat was stronger than abdominal meat, which may be associated with the content of carbonyl compounds and alcohols. |
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