Ultrasound-Assisted Extraction of Syzygium cumini Anthocyanins Using Natural Deep Eutectic Solvents

Syzygium cumini (S. cumini) is an excellent source of anthocyanins, which are valuable natural compounds with potential pharmacological and food-related applications. In this study, the combination of natural deep eutectic solvents and ultrasound-assisted extraction was explored as green alternatives to conventional solvents for efficient anthocyanin extraction from the pulp of S. cumini. Eight different solvent systems were prepared with choline chloride (Cho) and citric acid (Ci) as hydrogen bond acceptors and oxalic acid, lactic acid, fructose, ethylene glycol, 1,2-propanediol, urea and maltose (Oxa, Lac, Fru, Eth, Prop, Ur, Ma) as hydrogen bond donors. The solvent systems were prepared using heating, stirring, and ultrasonication methods. The extraction yield was optimized based on the selection of the best natural deep eutectic solvent mixture, ultrasonication time, and extraction temperature using a single-factor experimental methodology. It was found that choline chloride and propylene glycol (ChoProp) was the most efficient NADES system. The maximum extraction of anthocyanins was observed at 25 °C for 5 min of ultrasonication, resulting in a total anthocyanin content of 308.81 mg C3G/100 g dry extract. Furthermore, ChoProp served as an efficient solvent for polyphenol extraction, resulting in a total phenolic content of 1.6 mg GAE/g dry extract. The radical scavenging assay (87.4%) and ferric reducing antioxidant power (0.058) were approximately equivalent to conventional solvents, indicating the natural deep eutectic solvents as a potential alternative. Overall, the integrative technique of natural deep eutectic solvents and ultrasound-assisted extraction showed to be a promising green alternative for efficient anthocyanin extraction, where S. cumini proved to be a great source of anthocyanins, yielding higher total anthocyanin content.