Subcritical Water Extraction Enables the Production of Cichoric and Caftaric Acid-Standardized Echinacea purpurea Root Extracts with Defined Composition and Favorable Biological Properties

This study investigates subcritical water extraction (SWE) as an alternative to hydroalcoholic extraction for the production of Echinacea purpurea root extracts standardized to hydroxycinnamic acids (cichoric and caftaric acids). Extractions were performed at 100 °C, 125 °C, 150 °C, and 170 °C for 10–30 min. The recovery of cichoric and caftaric acids was significantly (p < 0.05) influenced by extraction temperature, with the highest values obtained within the range of 100–125 °C. Further experiments identified 110 °C for 10 min as the optimal condition, yielding the highest cumulative recovery of cichoric and caftaric acids (1.87 ± 0.10% of dry material). In the resulting dry extracts, SWE at 100–125 °C produced hydroxycinnamic acid contents of 5.5–7.1%, whereas the total dry extract yield in-creased from 24–28% at 100 °C to 40–41% at 150–170 °C (p < 0.05). Higher temperatures, however, reduced cichoric and caftaric acid cumulative content to 0.6–1.7% (p < 0.05), indicating a degradation of the target compounds. In contrast, total polyphenol recovery in-creased continuously with temperature, reaching 4.86% at 170 °C for 30 min. This was accompanied by marked increases in rutin, gallic and caffeic acid, reaching 458.5 mg/100 g dry weight (DW), 175.5 mg/100 g DW and 945.7 mg/100 g DW (p < 0.05), respectively, suggesting the release of bound phenolics following partial disruption of plant cell wall structures. SWE also enhanced the extraction of carbohydrates, uronic acids, fructans, proteins and organic acids, demonstrating an extensive temperature-dependent modification of the root matrix. 5-HMF was not detected in extracts obtained below 125 °C, but increased progressively at higher temperatures, reaching 200 mg/100 g (p < 0.05) at 170 °C. Biological evaluation in the human colorectal adenocarcinoma cell line (HT29) showed favorable cytocompatibility of SWE extracts, confirmed by cell viability, morphological assessment and low DNA damage in the Comet Assay. Overall, SWE enables the production of cichoric and caftaric acid-standardized E. purpurea extracts without organic solvents, supporting its application in pharmaceutical, nutraceutical, food and cosmeceutical products.