An approach to subcritical fluid and natural deep eutectic solvent-ultrasound assisted extractions as green alternatives for Pecan nutshell phenolic compounds recovery

Abstract

Green alternatives for Pecan nutshell phenolic compounds recovery were assessed in the present work. Subcritical fluid extraction and ultrasound-assisted extraction with natural deep eutectic solvent were optimized to maximize phenolic compounds extraction and antioxidant activities. Subcritical fluid was analyzed by varying temperature (180-220°C), flow rate (2.5-7.5 g/min) and solvent composition (0-100% (v/v) ethanol/water mixtures). The optimal Subcritical fluid method involved operating at 220°C with 50% (v/v) ethanol/water at a flow rate of 5 g/min, resulting in a remarkable 200% increase on total phenolic compounds and a substantial 500% increase on antioxidant activity measured by ferric reducing ability of plasma when compared to stirring, a conventional method used as control. Moreover, several ultrasound-assisted extractions with natural deep eutectic solvent were produced with choline chloride and lactic or malic acids; after selecting choline chloride-malic acid, the ratio and water % were optimized through response surface methodology. The optimal ultrasound-assisted extraction with natural deep eutectic solvent employed a 1:1 mol:mol ratio, with a water content of 35.82% (v/v), yielding a 39% and 25% increase on total phenolic compounds and ferric reducing ability of plasma compared to stirring, respectively. Finally, a full evaluation of the most relevant characteristics regarding process, estimation of equipment and extraction costs and a comparison regarding simplicity, safety, selectivity, cost vs. benefit and applicability among the employed methods was included. This research contributes to the development of environmentally friendly technologies and its advantages/drawbacks applied to phenolic compounds recovery from Pecan nutshell with potential applications in food, cosmetics and pharmaceutical industries.