Statistical optimization of ultrasound-assisted extraction of polyphenols from olive pomace

Ultrasound-assisted extraction (UAE) is a technique commonly used in combination with solvent extraction and effectively enhances the extraction of polyphenols. This technique has successfully solved the problem of polyphenols in biotechnology. The present study was carried out to optimize the extraction of phenolic compounds (total phenols, flavonoids, orthodiphenols, and flavonols) and the evaluation of antioxidant activities (reducing power and antiradical activity) from oil mill waste (OP, olive pomace). The three independent variables selected were sonication amplitude (20–100%), extraction time (2–20 min), and solvent acetone concentration (40–80%). The optimization study was carried out using the Box-Behnken design. The results revealed that all developed models regarding phenolic contents and antioxidant activities, through experimental design, expressed high levels of significance (F-values = 0.0004–0.0210) with good concordance between predicted and experimental data (R2 = 0.929–0.987). The optimal conditions for phenolic extraction and antioxidant activity were achieved using 57.34% acetone, 83.69% sonication amplitude, and 2 min of extraction. Under these conditions, the obtained contents for TPC, flavonoid, orthodiphenol, and flavonol were 23.43 g GAE/kg, 10.33 g CE/kg, 17.72 g GAE/kg, and 5.43 g QE/kg, respectively, resulting in a global desirability of 84.41%. Moreover, the predicted optimal conditions were experimentally validated. Considering all statistical parameters, it can be concluded that the developed models are suitable for achieving the highest recovery of phenolics from OP.