Effects of Heat Treatment and Transglutaminase on the Quality of Set Yoghurt

Abstract:In order to reveal the effect of heat treatment and transglutaminase(TGase) treated on the quality of set yoghurt, the set yoghurt milk was prepared with raw milk by different heat treatment(70℃ for 15 min,80℃ for 15 min,90℃ for 15 min,95℃ for 5 min),and different concentration TGase(0,5 and 10 U) along with fermentation. The total color variation value(ΔE),water holding capacity, hardness,pH and sensory characteristics of set yoghurt were measured. The results showed that the ΔE of set yoghurt(0 U TGase) increased by 18.86% with heat treatment temperature increasing from 70℃ to 95℃,and its water holding rate increased by 12.39%,hardness increased by 7.48%,and the pH decreased by 0.19 and 0.13 after storage for 24 h and 21 d, and finally the set yoghurt got a richer mastic. TGase treatment could improve the sensory characteristics(consistency,mouth feel,tissue structure) of set yoghurt,increase the water holding capacity,reduce ΔE and slow post-acidification rate. While its effect was positively correlated with the concentration of TGase. The set yoghurt heated at 95℃ for 5 min and added 10 U of TGase had better quality characteristics than other samples. Its ΔE was 8.11% lower than the set yoghurt at the same temperature without added TGase,its water holding rate increased by 5.56%,its pH decreased by 0.08 and 0.38 after storage for 24 h and 21 d, and its hardness had also been greatly improved by 23.30%. The above results had shown that heat treatment and TGase could synergistically improve the quality and gel structure of yoghurt. Heated at 95℃ for 5 min with 10 U TGase addition could be the best way to produce set yoghurt.