Effects of Tea Polyphenols and Thermal Pretreatment on the Gel Properties and Storage Stability of Yogurt

This study investigated the effects of tea polyphenols (TPs) and thermal pretreatment on the gel properties and storage stability of set yogurt. Yogurt formulations were prepared with TP concentrations ranging from 0% to 0.3% and subjected to two heat treatments of 65 °C and 95 °C. Rheological measurements (storage modulus G', loss modulus G″, and complex viscosity η*) showed that the addition of TPs improved gel viscoelastic properties, with greater effects under the 95 °C treatment. At a polyphenol level of 0.2%, the gel exhibited the highest stiffness and the most uniform microstructure, as confirmed by microscopy. Under 65 °C heating, increasing TP content led to reduced texture parameters, lower water-holding capacity, and greater syneresis, indicating an unstable gel. Conversely, the 95 °C-treated samples containing 0.2% TPs displayed optimal stability. During storage, all samples experienced declines in pH, water-holding capacity, and viscosity; however, the TP-enriched yogurts maintained significantly higher values for these parameters (p < 0.05) compared with controls, demonstrating superior structural retention. These results indicate that 0.2% TPs combined with 95 °C pretreatment improve yogurt gel properties and storage stability, with TPs showing potential as a functional ingredient for dairy applications.