It is likely that endogenous or intrinsic TGase forms the G–L bonds in protein during cooking, since a variety of living organisms contain TGase in their tissues and organs1 and 4. The temperature elevation in food materials during cooking is frequently very slow, such that endogenous TGase can exert enzymatic activity for some time. Thus, it is quite reasonable to conclude that cooked or processed foods contain greater amounts of the G–L moiety than raw food materials due to the catalytic activity of endogenous TGase.