Extraction of Bioactive Compounds from Fresh Blueberry Pomace Using Choline Chloride-Based Systems: Influence of Formulation and Treatment Conditions

Cold-press processing of blueberries for juice production generates a wet pomace that retains bioactive compounds of interest. To recover these compounds from the by-product, this study evaluated the extraction performance of five choline chloride-based natural deep eutectic solvents (NADES), formulated with urea, fructose, malic acid, oxalic acid, or lactic acid at a 1:1 molar ratio and containing 15% water, under three extraction conditions: heating with agitation, ultrasound, and microwave treatment. Six independent extracts were prepared for each combination. In each of six independent pressing operations, 250 g of fruit were processed, yielding 175.3 ± 1.6 g of juice and 70.0 ± 1.5 g of fresh pomace. Solvent formulation and extraction technology significantly affected the recovered amounts of phenolics, flavonoids, and monomeric anthocyanins. Heating with agitation using the choline chloride:lactic acid solvent produced the highest total phenolic and flavonoid values, at 667.43 ± 15.33 mg gallic acid equivalents and 256.36 ± 10.37 mg catechin equivalents per 100 g fresh pomace, respectively. The highest monomeric anthocyanin content was obtained with choline chloride:oxalic acid under heating (187.39 ± 7.18 mg cyanidin-3-glucoside equivalents per 100 g). The acidic formulations emerged as promising candidates for further analytical validation, chromatographic characterization, and process optimization.