Optimization of Ultrasound-Assisted Extraction of Natural Antioxidants from Sugar Apple (Annona squamosa L.) Peel Using Response Surface Methodology

Sugar apple (Annona squamosa L.) is a popular tropical fruit and its peel is a municipal waste. An ultrasound-assisted extraction method was developed for the recovery of natural antioxidants from sugar apple peel. Central composite design was used to optimize solvent concentration (13.2%-46.8%), ultrasonic time (33.2-66.8 min), and temperature (43.2-76.8 °C) for the recovery of natural antioxidants from sugar apple peel. The second-order polynomial models demonstrated a good fit of the quadratic models with the experimental results in respect to total phenolic content (TPC, R²=0.9524, p<0.0001), FRAP (R²=0.9743, p<0.0001), and TEAC (R²=0.9610, p<0.0001) values. The optimal extraction conditions were 20:1 (mL/g) of solvent-to-solid ratio, 32.68% acetone, and 67.23 °C for 42.54 min under ultrasonic irradiation. Under these conditions, the maximal yield of total phenolic content was 26.81 (mg GA/g FW). The experimental results obtained under optimal conditions agreed well with the predicted results. The application of ultrasound markedly decreased extraction time and improved the extraction efficiency, compared with the conventional methods.