Optimization of Ultrasonic-Assisted Extraction of Polyphenols, Anthocyanins, and Antioxidants from Raspberry (Rubus coreanus Miq.) Using Response Surface Methodology

Ultrasonic-assisted extraction (UAE) was employed for highly efficient extraction of polyphenols, anthocyanins, and antioxidants from raspberry. Process variables were investigated, including ethanol concentration, sonication time, and extraction temperature. A central composite design consisting of three variables and five levels was used to assess the significance of each process variable in UAE applied to raspberry. Analysis of variance confirmed the ethanol concentration as the most significant variable, and reduction of anthocyanins was not observed during UAE. Optimal UAE conditions were an ethanol concentration of 36.2 %, extraction time of 12.84 min, and temperature of 50 °C estimated using overlapped contour plots, which gave predicted maximal values for total polyphenol content (48.67 mg gallic acid equivalent/g), total anthocyanin content (15.23 mg cyanidin-3-glucoside equivalent/g), and antioxidant activity (253 μmol/L trolox equivalent). Verification experiments were carried out under optimal conditions, and good agreement was found between estimated values and experimental values, suggesting that the fitted model was valid and accurate for the UAE process.