Effects of casein on gelling properties of surimi paste

The effects of casein on the gelation of walleye pollack surimi paste were investigated. When the surimi paste with or without casein was preincubated (setting) at 25 degrees C for up to 12 h, followed by cooking at 90 degrees C for 30 min, the addition of casein interfered not only with heat-induced gelation but also setting response. The addition of 1% and 5% casein to the surimi paste decreased the myosin content by about 9% and 32% on a protein basis, respectively. Since casein did not show a composite reinforcing effect on the surimi gel, the dilution of myosin-myosin interaction may be a major cause of the inferior gelation. Although myosin heavy chain was a better substrate for transglutaminase (TGase) than casein, casein added into the surimi paste effectively inhibited the enzyme-catalyzed myosin heavy chain crosslinking, particularly depressed the formation of its large polymers (n greater than or equal to 3) during the setting, and resulted in the weakening of cooked gels. A large amount of casein added to actomyosin also inhibited the TGase-catalyzed cross-linking of myosin heavy chain. TGase catalyzed the formation of hybrid proteins from a mixture of actomyosin and casein, but their amounts seemed to be too small to influence the gelling properties of the surimi paste.