Efficient and selective extraction of oleanolic acid from grape pomace with dimethyl carbonate†

Grape pomace is a major winery solid residue and several tons are annually produced worldwide. Since it is a valuable source of high value-added compounds, many strategies have been implemented for its valorization. The extraction of bioactive molecules with a broad range of applications is certainly the most investigated topics. In this context, oleanolic acid, a triterpenoid with a relevant biological activity, has been recently detected in grape pomace in remarkable quantities (0.45 mg per gram of fresh pomace). Herein, we report on a selective extraction of oleanolic acid from grape pomace by using dimethyl carbonate (DMC), a recommended green solvent as a better alternative to fossil-based solvents. Chemical–physical properties, Hildebrand's solubility and Kamlet–Abboud–Taft parameters have been considered to select a greener alternative to fossil-based solvents and theoretical calculations have been performed to determine the interaction between DMC and the oleanolic acid. The obtained grape pomace extracts were characterized by means of NMR and LC-MS. DMC allows the recovery of oleanolic acid from grape pomace, due to its weak polarity and poor ability to form H-bonds, with a molar selectivity of 61%, thus promoting the adoption of alternative green and sustainable technologies for biomass residue valorization. Also, DMC was recycled and reused in three consecutive extractions and no significant losses in terms of oleanolic acid extraction yield were detected.