Sustainable valorization of cherry (Prunus avium L.) pomace waste via the combined use of (NA)DESs and bio-ILs

Abstract

Sweet cherry pomace waste (CPW) obtained after juice production still contains high amounts of dietary fiber and added value compounds such as polyphenols. For this reason, it can be employed as renewable feedstock to produce novel commodities, bioactive compounds and bio-functional materials. In this study, a sustainable biorefinery approach has been developed combining the use of natural deep eutectic solvents (NADESs) for the recovery of polyphenolic compounds and bio-based ionic liquids (bio-ILs) for the treatment and conversion of the remaining lignocellulosic residue into an ionogel. The extraction efficiency and selectivity of different classes of (NA)DESs were evaluated varying both the hydrogen bond acceptor, HBA (choline chloride (ChCl), betaine (Bet) and L-proline (Pro)) and the hydrogen bond donor, HBD (carboxylic acids and polyols). The extracted phenolic compounds were qualitatively and quantitatively analyzed by UHPLC-HR-ESI-MS leading to the identification of more than 25 compounds, classifiable into four main subclasses (phenolic acids, flavonoid glycosides, flavonoid aglycones, and anthocyanins). The majority of ChCl-based DESs improved the total phenol extraction compared to classical solvents (up to twice). ChCl : ethylene glycol 1 : 2 was identified as the best performing system in terms of total phenolic content (total phenol 759 ± 85 μg g⁻¹ of dried CPW) and was employed as the extraction medium for further optimization of the operative conditions and recycling study. The solvent was quantitatively recovered for three cycles with retention of the extraction efficiency towards all the identified subclasses of phenols. Finally, cholinium arginate (ChArg) allowed for obtaining cellulose enriched material (35 wt% of dried biomass) that was subsequently dissolved at 2 wt% in cholinium levulinate (ChLev) to prepare a weak physical ionogel, a functional biomaterial potentially useful in medical and pharmaceutical sectors.