Radio frequency assisted extraction of pectin from apple pomace: Process optimization and comparison with microwave and conventional methods

Abstract

Extraction methods directly influence the pectin yield (PY), physicochemical and structure properties from fresh fruits. Radio frequency assisted extraction (RFAE) was used for obtaining pectin from apple pomace by response surface methodology. The kinetics, physicochemical and structure properties of pectin used by RFAE, microwave assisted extraction (MWAE), and conventional extraction (CE) were compared under the same operating conditions. The optimized RFAE conditions include solvent pH of 2.2 (citric acid), heating temperature of 88 °C, and holding time of 19 min. The PY was 11.24 ± 0.69, 10.58 ± 0.59 and 7.46 ± 0.92%, respectively, for RFAE, MWAE and CE. The initial extraction rate of MWAE was larger than that of RFAE, but both of them were much larger than that of CE. Among three extracted samples, RFAE pectin showed the highest degree of esterification, galacturonic acid content and ABTS scavenging capacity with the lightest color appearance. FTIR, XRD and 1H NMR analysis also confirmed that the samples extracted from all three methods contained characteristic functional groups naturally existing in pectin, but no significant difference was observed in the main chemical structures among them. Surface morphology of both RFAE and MWAE showed rougher with more cracks as compared to a relatively intact and smoother surface observed in CE. Overall, RFAE can be considered as a promising extraction technology in terms of PY and quality as compared to MWAE and CE.