Optimization of PEF-assisted extraction of polyphenols from potato peels by using response surface methodology

In this study, conventional solid liquid extraction (SLE) and pulsed electric field (PEF)-assisted extraction of polyphenols from discs of potato peels (1 cm in diameter) were optimized using response surface methodology (RSM). The evaluation of the cell disintegration index (Zr), based on the measurement of electrical impedance of samples treated at different intensities (E = 0.25 - 3 kV/cm; WT = 1 - 20 k]/kg), was used to select suitable electrical conditions (1 kV/cm; 5 kJ/kg) to carry out subsequent PEF-assisted diffusion tests. The effect of ethanol concentration in water (0-100%), extraction time (30 - 240 min), and diffusion temperature (20-50 °C) on the extractability of phenolic compounds (Folin-Ciocalteu reagent), as well as on the antioxidant activity (DPPH) of the extracts from both untreated and PEF treated samples were investigated. The optimal set of process parameters predicted by the "central composite design" applied model, which gave the highest total phenolics yield (TPY), were: 54% ethanol, 233 min and 50 °C for the SLE, and 52% ethanol, 230 min and 50 °C for the PEF assisted extraction, giving a TPY of 1180 mg GAE/kg wet potato peels and 1295 mg GAE/kg wet potato peels, respectively. Coherently with these results, the antioxidant activities of extracts were 755 mg AAE/kg of wet potato peels for SLE and 859 mg AAE/kg of wet potato peels for PEF pre-treated samples. The highest increment obtained due to the PEF pre-treatment (104% increase in phenolic content, and 80% increase in antioxidant activity) was recorded when using water as solvent. Finally, HPLC analyses of 50% Ethanol extracts revealed that the concentration of the main phenolic compounds detected (chlorogenic, caffeic, syringic, protocatechuic and p-coumaric acids) were higher in the case of PEF-assisted extraction from potato peels, as compared to the conventional SLE.