Analysis And Evaluation Of Nutritional Composition In Chinese Soft-shelled Turtle(Trionyx Sinensis)

Evaluation of nutritive value is fundamental to understanding of foods. It contains many types of nutrients, including moisture, protein, fat, carbohydrate, ash, vitamin, minerals, etc. Many of the nutrients, protein quality is a very important indicator reflecting the nutritive value of foods. Chinese soft-shelled turtle is a traditional food in china, and is good for our health, whose body is a treasure, the various parts of the body could be used as medicine.In this paper, the general nutrition composition, amino acids and fatty acids in muscle(legs and carina) of Trionyx sinensis were investigated. In addition, the protein composition were separated, then analyzed the isolated components of legs by studying amino acid composition and molecular weight distribution. Finally, in vitro and in vivo digestion trials were made for the determination of protein digestibility of legs muscle before and after heat-treatment. The main research results are as follows.Compared with other animals, such as bullfrog, giant salamander, chub, chicken, pork and beef, Trionyx sinensis showed lower content of crude fat. The protein content in carina is 20.97 g/100 g sample which was significantly higher(p<0.05) than that in legs 18.20 g/100 g, while crude fat content was very significantly lower(p<0.01) than that of legs, they were 0.42 g/100 g and 0.96 g/100 g, respectively. So as far as content of nutrients, carina was more fit for the trends of consumer demands. In the aspect of amino acids(AA), 18 kinds of AA were detected in muscle. In legs, the glutamic content(2.84g/100g) was the highest. The ratio of total essential AA(TEAA) to total amino acid was 40.83%, the ratio of TEAA to nonessential AA(TNEAA) was 69.01%, which was fit to the good protein resource reference values recommended by FAO/WHO. In carina, the content of TEAA was lower than the protein recommended pattern, tryptophan was the first limiting acid, while it was rich in delicious AA(DAA), which was dominated by glycine. The differences among the two tissues may related with protein composition, maybe the carina contained more collagen. In terms of fatty acids(FA), 20 and 12 kinds of FA were determined in legs and carina, respectively. The content of polyunsaturated FA(PUFA) in legs(25.30%) was significantly higher than that in carina(22.17%), especially DHA. According to AA and FA composition, it was showed that the the legs muscle of Chinese soft-shelled turtle was of good quality compared with carina muscle.Depending on the solubility, the protein composition was separated. Significant differences between legs and carina was found(p<0.05). Composition of protein in carina was relatively onefold, it contained 92.25% stroma protein, then is myosinogen protein 5.60% and myofibril protein 2.07%. The protein composition of legs was contrary to carina. In descending order of content, they were myofibril protein(39.47%), myosinogen protein(31.79%) and stroma protein(28.72%). Further, amino acid composition and molecular weight distribution of the isolated components of legs were studied. According to content of AA and amino acid score(AAS), it was showed that excepted for stroma protein, AA composition of other components met the FAO/WHO standard. The characteristic of stromat protein was similar with carina, it had lower TEAA but higher DAA content. The result of SDS-PAGE electrophoresis displayed that the molecular weight of sarcoplasmic protein, myofibrillar protein, stroma protein were 10-90 k Da, 20-100 k Da, 100-200 k Da, respectively.From the digestibility perspective, in vivo and in vitro digestion trials were made. In addition, digestibility the difference between raw and heat-treated legs muscle were studied. The results showed that, before heat-treatment, the in vitro and in vivo digestibility were 83.68% and 95.05%, after heat-treatment, that heat-treatment increased significantly(p<0.05). Based on AAS and true digestibility, the protein digestibility-corrected amino acid scores(PDCAAS) was evaluated. Since the cooking loss, PDCAAS reduced from 100% to 76.94%. Compared the digestibility and PDCAAS with beef, Trionyx sinensis showed higher nutritive value.