Recovery of antioxidant and antiproliferative compounds from watercress using pressurized fluid extraction

Abstract

In this work, pressurized fluid extraction was explored to recover isothiocyanates (ITCs) and phenolic compounds from watercress. Pretreatment of the raw material was studied, using different conditions of temperature (25 °C; 35 °C), pressure (P_atm; 25 MPa), incubation time (0; 30; 60; 120 min) and moisture content (125; 250; 900% of water, dry basis), aiming at promoting the enzymatic hydrolysis of glucosinolates in ITCs. Extractions of ITCs were performed with supercritical CO₂, and different mixtures of CO₂ : ethanol (0–50, % w/w) were applied to obtain phenolic-enriched ITCs extracts. Extractions were performed at 35 °C and 25 MPa for 2 h and extracts analyzed concerning total ITCs, phenethyl isothiocyanate (PEITC) content, phenolic composition, antioxidant capacity (using ORAC, HORAC and HOSC assays) and antiproliferative effect in a human colorectal cancer cell line (HT-29). Results showed that supercritical CO₂ was highly selective in isolating ITCs from watercress (up to 31.7 ± 1.6 μmol ITC per g). When mixtures of CO₂ : ethanol were used, extraction of phenolics (up to 10.1 ± 0.8 mg GAE per g) and antioxidants (up to 204.4 ± 21.5 μmol TE per g concerning ORAC, 70.8 ± 10.7 μmol CAE per g for HORAC and 189.5 ± 22.9 μmol TE per g for HOSC), was promoted. PEITC was the main compound responsible for the inhibition of cancer cell growth of all extracts (EC_{5024 h} = 27.8 ± 1.9 μM PEITC). However, extracts obtained by supercritical CO₂ extraction after a 30 minute incubation period with CO₂ and with CO₂ : ethanol mixtures (80 : 20 and 60 : 40, % w/w) were revealed to be effective in isolating other bioactive compounds that enhanced the antiproliferative response of extracts (EC_{5024 h} values of 23.1 ± 0.9; 20.7 ± 1.9 and 19.8 ± 0.7 μM PEITC, respectively).