Optimization of Subcritical Water Extraction Process for Polyphenols from Cinchona calisaya and Their Activity Analysis

This study expands research on <i>Cinchona calisaya</i>, which has traditionally focused on alkaloids, to address the insufficient comprehensive utilization of its resources. It is the first to explore the feasibility of extracting phenolic compounds from <i>Cinchona calisaya</i> using subcritical water extraction (SCWE) technology. Combining single-factor experiments with Box-Behnken design-response surface methodology (BBD-RSM), the study optimized three key process parameters, namely extraction temperature, extraction time, and liquid-to-solid ratio, with total phenolic content (TPC) as the response variable. Optimal extraction conditions were 165 °C, 20 min, and a liquid-to-solid ratio of 70:1 mL/g. Under these conditions, the TPC values were 98.41 ± 1.06 mg/g for bark and 37.96 ± 1.18 mg/g for heartwood, significantly higher than those obtained by traditional hot water extraction (THWE). Ultra-high performance liquid chromatography-Q-orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS) identified 1198 and 1156 metabolites in the bark and heartwood, respectively, with a higher content of phenolic compounds in the heartwood. The extracts showed strong inhibitory activity against <i>Staphylococcus aureus</i>, weak inhibitory activity against <i>Escherichia coli</i> at high concentrations, and no inhibitory effect on <i>Candida albicans</i>. This study provides a theoretical basis and technical support for the comprehensive utilization of <i>Cinchona calisaya</i> resources and the green development of natural antioxidants and antimicrobial agents.