Optimization of extraction conditions of antioxidant phenolic compounds from mashua (Tropaeolum tuberosum Ruíz & Pavón) tubers

Optimal conditions for the extraction of phenolic compounds, anthocyanins, flavanols and ORAC antioxidant activity for two mashua genotypes were determined using the conventional liquid-solid method. Phenolic contents and antioxidant activity were affected by the type of solvent, pH level, solvent-water ratio and extraction time. In general, no significant differences in total phenolic recovery and ORAC values were observed when 90% methanol or methanol/acetone/water (45/45/10), both with 0.1% HCl, were used. By contrast, the 90% methanol solution with 0.1% HCl extracted the highest level of anthocyanins, whereas the solvent mixture extracted the highest level of flavanols. The purified extracts from the mashua genotypes presented total phenolics and ORAC contents within the ranges 14.4-18.7 mg gallic acid equivalents/g mashua dry matter (DM) and 221-359 μmol of trolox equivalents/g mashua DM, respectively. The HPLC-DAD phenolic profiles obtained for the purified phenolic extracts for both mashua genotypes showed differences in proportions (% total area at 280 and 520 nm) depending on the solvents selected in this study. The high content of phenolic compounds and antioxidant activity found in the purified extracts for both mashua genotypes indicated that mashua extracts might be considered as a potential source of nutraceuticals in the future.