Optimising ultrasound-assisted extraction conditions for maximising phenolic, flavonoid content and antioxidant activity in hog plum peel and seed: A response surface methodology approach

This study optimised ultrasound-assisted extraction (UAE) temperature, time, and ethanol concentration to investigate total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH free radical scavenging activity assay) from hog plum peel and seed. Optimisation used Response Surface Methodology (RSM) with a Box-Behnken design (BBD) of three factors at three levels. The variables for both peel and seed were temperature (40–60 °C), time (30–60 min), and ethanol concentrations (40–80 %). Fifteen experimental runs were conducted, using a second-order polynomial model (quadratic) and analysis of variance (ANOVA) to predict the responses and validate the model. The results revealed that the moisture, protein, fat, crude fibre, ash, and carbohydrate content of hog plum seed and peel differences in their nutrient content. Additionally, peel contains a TPC of 95–104 mg GAE/100 g DM, DPPH activity of 68–92 %, and TFC of 1.622–2.312 mg QE/g DM, while TPC varies between 97 and 110 mg GAE/100 g DM, DPPH activity ranges from 71 to 95 %, and TFC of 1–22 mg QE/g DM for seed. The R² value of both peel and seed for TPC, TFC, and DPPH activity was 0.99, indicating that the quadratic model is satisfactory for analysing interactions between response and independent variables. Furthermore, RSM analysis identified the optimal extraction conditions of both peel and seed for maximising TPC, TFC, and DPPH activity at a temperature of 59.82 °C, a time of 41.08 min, and 76.64 % ethanol concentration. Under the optimal settings, the observed values were 108.34 ± 7.23 (peel) and 101.45 ± 3.65 mg GAE/100 g DM (seed) for TPC, 2.98 ± 2.10 (peel), and 3.98 ± 1.34 mg QE/g DM (seed) for TFC, and 85.13 ± 5.43 (peel), and 84.35 ± 4.10 % (seed) for DPPH activity. This study establishes a framework for further investigation into UAE parameters and extraction solvents to enhance the extraction efficiency of hog plum seed and peel.