Synergistic Effects of Pressure–Temperature Conditions on Quality, Enzymatic Stability, and Functional Properties of Yanang Leaf Juice

Yanang ( Tiliacora triandra ) leaf juice is highly susceptible to enzymatic browning, chlorophyll degradation, and microbial spoilage after extraction, limiting its industrial utilization. This study investigated the effects of high pressure processing (HPP) under different pressure–temperature combinations on the physicochemical properties, enzymatic activity, bioactive compounds, antioxidant capacity, microbiological quality, and sensory attributes of Yanang leaf juice. Samples were treated at 400–600 MPa and 25–50°C for 20 min. Combined high pressure and moderate temperature conditions, particularly 600 MPa/50°C, markedly improved product quality by enhancing phenolic and flavonoid contents, antioxidant capacity, enzyme inactivation, and microbial reduction. Polyphenol oxidase and peroxidase residual activities were reduced to 74.58% and 60.73%, respectively, under the most intensive treatment condition. In contrast, ascorbic acid and chlorophyll contents showed partial degradation at elevated temperatures, indicating sensitivity to thermal effects. HPP treatments also reduced microbial populations to levels complying with Thai Community Product Standard (TCPS 1443/2009) while maintaining desirable sensory attributes. These findings demonstrate that HPP combined with moderate temperature is a promising non-thermal technology for producing safe, high-quality Yanang leaf juice with enhanced functional properties.