The Effect of Transglutaminase and Protease A2SD on Sensory Characters and Physical–Chemical Properties of Soy Sauce

<i>N-acetyl-amino acids</i> were additives for improving kokumi of soy sauce, which was obtained by Transglutaminase (TG) and protease A2SD using amino acid and acetic acid in aqueous solution. In this study, we studied sensory characters and physical-cheimcal properties of soy sauce treated with TG, TG and acetic acid, protease A2SD, protease A2SD and acetic acid (T, TA, P and PA). T and P had higher umami, sweetness, saltiness, kokumi, amino acid nitrogen and colour, and lower bitterness than control. Addition of acetic acid could increase this effect which increased by 103%, 17%, 18%, 18%, 5%, 21%, respectively, and decreased by 30% in TA. Chemical compound analysis indicated soy sauce treated with TG and protease A2SD had lower molecular weight distribution and higher free amino acids, <i>N-acetyl-amino acids</i> and <i>N-acetyl-dipeptides</i> content, which might resulted in taste difference of different soy sauces. This study offered an alternative method for improving kokumi of soy sauce by <i>N-acetyl-amino acids</i>.