Application of green deep eutectic solvents for anthocyanins extraction from grape pomace: Optimization, stability, antioxidant activity, and molecular dynamic simulation

The wine-making industry produces a large amount of grape pomace, which is rich in anthocyanins. To avoid wasting these resources, choline chloride: lactic acid (molar ratio of 1:2) (DES-1) was selected as the optimal solvent. The optimal extraction conditions were as follows: temperature 60 degrees C, time 60 min, water content 25%. The anthocyanins yield was 5.73 mg (cyanidin-3-glucoside) equivalent/g under the optimal conditions, which was significantly higher than that obtained by DES-3 (Choline chloride: 1,4 butanediol), DES-5 (Choline chloride: 1,2 propylene glycol), and ethanol. The DES-1 extract showed significant higher color stability and antioxidant activities compared with the anthocyanins extracted by DES-3, DES-5, and ethanol. A total of eight individual anthocyanin compounds were identified in each extract, with delphinidin 3-O-glucoside, peonidin 3-O- glucoside, petunidin, and delphinidin as the dominant compounds. Molecular dynamics simulation confirmed that DES-1 system showed a larger average number of hydrogen bonds (11.63), average lifetime of hydrogen bonds (364.21 ps) and with a reduced total interaction energy (-706.82 kJ/moL), thus improving the extraction efficiency and stability of anthocyanins. This study would provide new protocols for the extraction of anthocyanins from grape pomace.