Effect of Adding Glutamine Transaminase on the Quality of Set-style Yogurt

The objective of this work was to study the difference of physical and chemical indexes and sensory indexes between set-style yogurt with TG enzyme and plain set-style yogurt (without TG enzyme) in the fermentation process. The changes of acidity, viscosity, hardness, water holding capacity and viable count of yogurt during fermentation were measured by phenolphthalein indicator method, rheometer, texture analyzer, centrifugation and plate counting method, respectively. The changes of color, taste and smell were measured by electronic eye, electronic tongue and electronic nose, respectively, and sensory evaluation was carried out. The results showed that adding 0~5 U TG enzyme per gram of milk protein, the acidity of yogurt at the end of fermentation was within the range of 71.12~73.64 ^oT, and there was no significant difference in the acidity of yogurt (P>0.05). During the fermentation process, the viscosity and hardness increased significantly after 3 h (P<0.05), and the viscosity and hardness of set-style yogurt with TG enzyme increased significantly at the end of fermentation (P<0.05). With the increase of TG enzyme content, the water holding capacity increased significantly (P<0.05). Adding different concentrations of TG enzyme had no significant effect on the number of viable bacteria in set-style yogurt (P>0.05). The main color number of TG enzyme set-style yoghurt and common set-style yoghurt were both 4095, and there was no significant difference in color at the end of fermentation (P>0.05). By principal component analysis, adding different concentrations of TG enzyme after fermentation had no significant effect on the taste and smell of yogurt (P>0.05). According to sensory evaluation, yogurt that 1 g milk protein supplemented with 2 U TG enzyme had the best sensory. Therefore, compared with the plain set-style yogurt without TG enzyme, the coagulated yogurt with TG enzyme was not significantly different in acidity, live bacteria count, color, taste and odor (P>0.05); it was significantly higher in viscosity, hardness and water-holding capacity (P<0.05), and the addition of appropriate amount of TG enzyme was beneficial to the improvement of the quality of coagulated yogurt.