Purification And Characterization Of Endogenous Transglutaminase From Bighead Carp And Evaluation Of Its Effect On Setting

The bighead carp (Hypophthalmichthys nobilis) is delicious and nutritious, which has been known as one of the four important freshwater fish in china. The bighead carp is a lucrative aquaculture fish, however the deep processing rate of bighead carp is very low. As fish stocks are in free-fall all over the world the processing of bighead carp to obtain surimi can be a good alternative use for this abundant resource. In this paper the nutrition of bighead carp were analyzed. Transglutaminase (TGase) from bighead carp muscle was successfully purified to electrophoretic homogeneity after three purification steps and the biochemical characteristics of this novel enzyme was investigated. Also, the optium conditions for setting were evaluated. The difference in flavor compositions between bighead carp and bighead carp surimi was also analyzed. The bighead carp has a rich amount of protein.Its essential amino acid index (EAAI) reached91.15, indicating that bighead carp is a high quality protein source with a well-balanced amino acid composition. The amount of polyunsaturated fatty acid (PUFA) was42.15%of total fatty acid in bighead carp. The total amount of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) was15.11%. Also the bighead carp has a rich amount of potassium, magnesium, calcium, and sodium. And inorganic arsenic, methyl mercury, lead content is lower than the limit standard of toxic and harmful substances in aquatic products.The bighead carp is eutrophy which makes it an ideal material for producing surimi.Setting is important in surimi production, endogenous TGase has been proved to be essectial in setting. So an evaluation on the properties of endogenous TGase can provide the theoretical guidance for processing bighead surimi. In this chapter, the TGase from muscle of bighead carp was purified and characterised. TGase was purified after three steps. The yield and purification fold was5.69%,6.25, respectively. TGase’s molecular weight was estimated to be around62kDa. Optimal temperature for TGase was37-45℃. Optimal pH for TGase was around7. TGase from bighead carp was calcium-dependent and the optimal concentration was at0.42mM. TGase activity decreased as the NaCl concentration increased. Dthiothreitol (DTT) could increase TGase activity. The optimal concentration of DTT was at4.2mM. Ethylene diaminete traacetic acid (EDTA) could totally inhibit TGase activity. TGase was strongly inactivated by Cu2+, Zn2+, Pb2+, Ba2+and N-ethylmaleimide.In order to evaluate the effect of endogenous TGase in setting, we studied the effect of different setting conditions, TGase activator and inhibitor on setting. The optimal setting temperature for bighead carp surimi was40℃, the suitable setting time was one hour. With addition of calcium ions, gel stength increased with calcium chloride concentration. The decrease in Myosin Heavy Chain (MHC) was shown on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and protein solubility decreased as calcium ions increased. This result indicated that TGase activity increased with the addition of calcium ions which could lead to more polymerization of MHC. Gel strength decreased at the presence of EDTA and Cu2+, Zn2+, Pb2+, Ba2+. Also MHC was more retained and protein solubility increased with increasing concentration of EDTA and the presence of Cu2+, Zn2+, Pb2+, Ba2+. This indicated that these TGase inhibitors could inhibit TGase acticity leading to lower gel strength.In order to understand the volatile flavor compounds of bighead carp, we studied the difference between bighead carp surimi and bighead carp. There were34kinds of volatile flavor compounds in bighead carp surimi and41kinds of volatile flavor compounds in bighead carp. The content of unsaturated alcohols could be decreased by processing bighead carp into surimi, which could lead to the flavor loss of bighead carp surimi.The key odor compounds for bighead carp surimi was1-Octen-3-ol, Tetradecanal, Hexanal, Myrcene, Nonanal, Naphthalene,2-Nonanone, Dibutyl Phthalate. While the key odor compounds for bighead carp was1-Octen-3-ol, Octanal, Nonanal,1-Heptanol, Tetradecanal, Hexanal.