Effect of cold enzymatic treatment of milk by transglutaminase on textural properties of yogurt

Protein gel is mainly established by weak noncovalent interactions. The introduction of new covalent bonds leads to gel formation with different structure and properties. It has been supposed that heightening the new protein cross linking by transglutaminase (TG) increases the degree of protein polymerization and thereby improves the physical and sensory properties of the yogurt. Therefore, the purpose of this study was to investigate the effect of cold enzymatic treatment of the milk by transglutaminase on the yogurt textural properties. The transglutaminase enzyme at 4 concentration levels (0, 0.01, 0.02, and 0.03 %) and 3 different incubation time (12, 24 and 48 h) was applied at 5°C. The results showed that milk treatment by TG at different periods of incubation can improve the textural characteristics, increase viscosity and decrease syneresis of the yogurt. All treated samples with different TG levels had better texture and consistency than control sample (without enzyme). For instance, by utilizing 0.01 per cent TG, the hardness and consistency significantly increased from 0.096 to 0.131 g and 0.872 to 1.049 g/s, respectively. Among yogurts, sample containing 0.03 per cent TG incubated for 48 h had the highest hardness and consistency and its mean values during 20 days of storage were recorded as 0.204 g and 1.645 g/s, respectively. However, results indicated that sample containing 0.03 per cent TG incubated for 24 h had significantly higher viscosity (24.32 Pa.s) than other yogurts.