New approaches for the effective valorization of papaya seeds: Extraction of proteins,phenolic compounds,carbohydrates, and isothiocyanates assisted by pulsed electric energy

The study compares the efficiency of common aqueous extraction (CE) at different pH (2.5–11) and temperatures (20–60 °C) and extraction assisted by pulsed electric energy (pulsed electric fields, PEF or high voltage electrical discharges, HVED) of nutritionally valuable and antioxidant compounds from papaya seeds. The exponential decay pulses with initial electric field strengths of ≈ 13.3 kV/cm and ≈ 40 kV/cm for PEF and HVED treatments, respectively, were used. The number of pulses n was changed within 1–2000. The impacts of temperature and pH on extraction efficiency of different components (proteins, total phenolic compounds, carbohydrates, isothiocyanates) and antioxidant capacity were ambiguous. The highest values of nutritionally valuable and antioxidant compounds were obtained for HVED-assisted extraction. However, the application of HVED-treatment may produce undesirable contaminants (chemical products of electrolysis, free reactive radicals, etc.) and extracts were unstable and cloudy. On the other hand, the application of the two-stage procedure PEF + supplementary aqueous extraction (+ SAE) that include PEF-assisted extraction as the first step, and + SAE at 50 °C, pH = 7 during 3 h as the second step, allowed noticeable enhancement of the yields (+ 200%) and antioxidant capacities (+ 20%) even at neutral pH. This method has high prospects of industrial applications for release of valuable components from papaya seeds.