Effect of epigallocatechin gallate on the fermentative and physicochemical properties of fermented milk

Yogurt, a traditional fermented dairy product, is made with a starter that contains Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The aim of this study was to investigate the effects of different concentrations of epigallocatechin gallate (EGCG; 0, 0.5, 1.0, 3.0, and 5.0 mg/mL) on the growth, metabolism, and acid production of lactic acid bacteria, as well as the texture, stability, and antioxidant activity of fermented milk (yogurt). The results showed that a low concentration of EGCG had no significant effect on the acid production capacity of the starter or on the water-holding capacity of the yogurt but did increase its viscosity. A high concentration (5.0 mg/mL) of EGCG delayed the acid production rate of the starter and decreased the water-holding capacity, but significantly increased the antioxidant activity of yogurt. The addition of EGCG significantly increased the hardness of yogurt. Therefore, EGCG can improve the texture of fermented milk and enhance its antioxidant activity and stability, thus improving the overall quality of yogurt.