Abstract
Selecting factors that significantly affect the extraction process and optimizing them are essential to obtain high extraction efficiency. This study aimed at optimizing the ultrasonic-assisted extraction (UAE) of polyphenols from Romanian blackthorn fruits using aqueous solutions of ethanol as green extraction solvents. Six process factors, including solvent/plant material ratio (R(LS) = 4.95-15.1 cm(3)/g), ethanol concentration in the extraction solvent (c(et) = 16.4-83.6%), extraction temperature (t = 30-70 °C), pH of the solvent (pH = 2-7), amplitude of the ultrasonic probe (A = 30-70%), and extraction time (τ = 5-15 min), were screened and optimized based on a Plackett-Burman design (PBD) and a central composite design (CCD). Statistical analysis indicated that R(LS), c(et), and t significantly affected the process response variables in terms of total phenolic content (TPC), total anthocyanin content (TAC), and antioxidant capacity (AC). Under optimal conditions (R(LS)(,opt) = 15.1 cm(3)/g, c(et)(,opt) = 33.2%, t(opt) = 66.8 °C, pH(opt) = 7, A(opt) = 50%, and τ(opt) = 10 min), the following levels of response variables were experimentally determined: TPC(opt) = 14.45 ± 0.718 mg GAE/g DM, TAC(opt) = 0.405 ± 0.057 mg C3GE/g DM, and AC(opt) = 16.75 ± 1.144 mg TE/g DM. Six phenolic compounds were identified in the extract obtained at optimal levels of process factors, i.e., rutin (7.12 ± 0.06 mg/100 g DM), protocatechuic acid (6.83 ± 0.01 mg/100 g DM), neochlorogenic acid (4.88 ± 0.01 mg/100 g DM), vanillic acid (3.70 ± 0.01 mg/100 g DM), chlorogenic acid (1.93 ± 0.02 mg/100 g DM), and caffeic acid (1.51 ± 0.01 mg/100 g DM).