Simple preparation and purification of citrus pectic oligosaccharides: structural analysis and antioxidant potential

Pectic oligosaccharides (POS) exhibit promising bioactive properties, primarily attributed to their simple structure, low viscosity, high solubility, and low molecular weight (Mw). In this study, a simple method based on the Fenton reaction and ethanol precipitation was used to prepare and isolate citrus pectic oligosaccharides (CPOS). The structural characteristics of the resulting CPOS were analyzed using FTIR, SEM, NMR, and UPLC-Q-TOF-MS, and their antioxidant activities were evaluated. Structural characterization revealed that the obtained CPOS consisted mainly of galacturonic acid (GalA). Further analysis via NMR and UPLC-Q-TOF-MS confirmed that CPOS with a degree of polymerization (DP) up to 13 was rich in GalA and galactose (Gal). Antioxidant activity assays demonstrated that CPOS exhibited strong DPPH (91.57% at 2 mg/mL) and ABTS (87.14% at 1 mg/mL) scavenging rates. This study indicated that a simple method based on Fenton reaction and ethanol precipitation can be used to produce CPOS with antioxidant activity, providing a technical reference for the industrialized low-cost production of POS and the development of functional food ingredients.