Deep eutectic solvents to extract anthocyanins from red grape skins: Experimental and computational approaches for solvent selection

Resumen

Grape skins are a winery by-product with a great potential as source of phenolic compounds tobe used as antioxidant in dietary supplements. In red grape skins, anthocyanins are water-solublepigments which stand out as food colouring. They are the 3-O-monoglucosides and 3-O-acylatedmonoglucosides of the main anthocyanidins (delphinidin, cyanidin, petunidin, peonidin andmalvidin). Deep eutectic solvents (DES) have been proposed as a sustainable and green methodfor the extraction of bioactive compounds from agri-food industry wastes and as a safe alternativefor nutritional, pharmaceutical and cosmetic applications because they are more respectful of theenvironment and avoid the safety issues that traditional organic solvents entail due to their toxicity,volatility and flammability. In silico studies using COSMO-RS (COnductor-like Screening MOdelfor Realistic Solvents) allows DES screening for the solute extraction. They are based on thecalculation of solute and DES molecules -profiles and the activity coefficients at infinite dilution( ) of the solute in the DES. In this communication, the results of COSMO-RS with malvidin-3-O-glucoside and malvidin-3-O-(6-p-coumaroyl)glucoside as model solutes for a DES screeningto find mixtures with high affinity for these compounds are presented. The computational studyshowed that potassium carbonate, sodium acetate and sodium propionate were better candidatesas hydrogen bond acceptors (HBA) than those reported to date in literature for the recovery ofanthocyanins from agri-food by-products. Moreover, the efficiencies of the ultrasound-assistedextraction of anthocyanins using different choline chloride and betaine-based DES and thoseobtained with the novel DES suggested by COSMO-RS are compared. Finally, to establish the mostfavourable extraction conditions, a study of the sonication time and the aqueous percentage in theDES was carried out using a design of experiments and the response surface methodology. The useof microwave-assisted extraction and the effect of temperature on anthocyanin recovery was alsostudied. Anthocyanins in the extracts were identified by LC-MS/MS, and their concentrations weredetermined by HPLC-vis (520nm).