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

## TL;DR

This study explores a new method to extract polyphenols from Cinchona calisaya using subcritical water, showing better results than traditional methods and potential antimicrobial properties.

## Contribution

The first study to use subcritical water extraction for polyphenols from Cinchona calisaya, optimizing key parameters and analyzing antimicrobial activity.

## Key findings

- Optimal extraction conditions achieved higher total phenolic content in bark and heartwood compared to traditional hot water extraction.
- Heartwood contained a higher content of phenolic compounds than bark, as identified by UHPLC-Q-Orbitrap HRMS.
- Extracts showed strong inhibition of Staphylococcus aureus and weak inhibition of Escherichia coli at high concentrations.

## Abstract

This study expands research on Cinchona calisaya, 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 Cinchona calisaya 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 Staphylococcus aureus, weak inhibitory activity against Escherichia coli at high concentrations, and no inhibitory effect on Candida albicans. This study provides a theoretical basis and technical support for the comprehensive utilization of Cinchona calisaya resources and the green development of natural antioxidants and antimicrobial agents.