The Effect Of Transglutaminase On The Gel Character Of Grass Carp Surimi

Surimi products occupies an important position in processing industry of aquatic products. The raw material of surimi and surimi products mostly are seafood. But the supply of seafood is reducing and it can't meet the market demands of surimi and surimi products, because marine fishing and aqua culture production is stagnated to varying degrees. Therefore the development of freshwater surimi products is an important issue in the future surimi processing industry. However the gelation of freshwater surimi is generally poor, especially after frozen storage. It has been found that transglutaminase can enhance surimi gel strength. In this thesis which focuced on grass carp, we studied the characterization of transglutaminase (TGase) from grass carp under different conditions, effects of FTG and MTG on cross-linking of natural actomyosin, and effects of MTG on gel strength of grass carp.The activity of TGase from grass carp can be affected by PH, setting temperature, ionic strength, activator, inhibitor, frozen storage time and other factors. The results showed that optimal pH and optimal temperature of transglutaminase from grass carp were 8-9 and 25-45℃, respectively. It could be activated by calcium. Dithiothreitol (DTT) at low concentrations (0～1 mM)can protect the active groups of enzyme, so as to increase the enzyme activity. Cu2+,Ba2+,Zn2+,Mn2+,Fe2+,Pb2+,Fe3+,Li+ Mg2+,K+,Na+ and other metal ions can inhibit the activity of TGase, and even lead to enzyme inactivation. Enzyme activity can also be affected by frozen storage time of surimi, enzyme activity decreases with frozen storage time.It was measured that the concentration of natural actomyosin (NAM) in solution which was added TGase was lower than which wasn't added in the heating process. It indicated adding TGase in solution can enhance the craoss-linking of NAM. Cross-linking of NAM in solution was more improved by MTG when MTG and FTG were added to solution both at 3 U TGase/ml. The concentration of NAM was greatly affected by temperature. It reduced to a minimum in 40～45℃. It indicated the cross-linking of NAM was best in this temperature. As the temperature increased further, the cross-linking of NAM significantly reduced, probably because of cathepsin is activated in higher temperatures.Surimi gel strength of grass carp was biggest under sunch conditions as 1～1.5% enzyme dosage, setting 0.5h at 42℃with natural PH value. Studies on whiteness, water holding capacity, cooking-loss of surimi gels under different conditions have shown whiteness of surimi gels had a certain relationship to gel strength and water content of surimi gels, and water holding capacity and cooking-loss of surimi gels is generally positively related to the gel strength of surimi. Calcium could improve the gel strength of surimi in concentration of 20-50mmol/kg. The gelation of surimi became bad by adding EDTA or NHUCl.Under optimized conditions, surimis adding potato starch, wheat starch or corn starch would form good gels. The adding amount of potato starch in 10～15%, surimi gels quality was better. The adding amount of water in 15～25%, surimi gels quality was better.