Optimization of ultrasound assisted organic acid extraction of pectin from pomelo peel by response surface methodology and its preliminary characterization

The approach of converting fruit by-products to produce value-added products contributes to sustainable development and environmental protection. Ultrasound assisted extraction technique was applied to extract pectin from waste pomelo peel (PP) using eco-friendly organic acid (citric acid). A Box-Behnken design (BBD) of response surface methodology (RSM) was employed to optimize the extraction conditions and investigate the individual and interactive effect of process variables (citric acid concentration, ultrasound temperature and ultrasound power) on the pectin yield. A second-order polynomial model was developed using multiple regression analysis and it showed higher adequate in predicting the pectin yield. The results showed that the maximum pectin yield of 21.68% was obtained at optimal conditions of citric acid concentration 1.66%, ultrasound temperature 75 °C and ultrasound power 191 W. The optimized pectin was classified as high methoxyl pectin due to its high esterification degree 67.26 ± 0.32%. The galacturonic acid content and ash content of the pectin were 82.89 ± 1.35% and 1.47 ± 0.21%, respectively, indicating its higher degree of purity. In addition, the pectin presented higher emulsion properties, emulsion activity of 54.3% and the values of emulsion stability of 76.9% to 85.7%. The PP pectin presented a smooth, but wrinkled and loosen surface. The pectin degradation was found in the temperature range from about 220 to 280 °C.