Abstract
Four citrus pectins were extracted from different discarded citrus peels. PPG, CJ, and QC pectins presented degrees of esterification (DE) values that exceeded 80%; in contrast, WG pectin presented a notably lower DE, which was reduced to approximately 65%. All four pectins are composed of seven monosaccharides: galacturonic acid, arabinose, galactose, glucose, rhamnose, mannose, and xylose, with galacturonic acid emerging as the predominant constituent (more than 50%). The molecular weights (Mws) of the four pectins all exceeded 100 kDa. Two Aureobasidium strains (40 and 44), which were isolated from CWs, harboured genomes enriched with pectin-depolymerizing carbohydrate-active enzymes (CAZymes). Following temperature and pH optimization of the pectin-degrading enzyme systems in the two black yeast strains, both effectively depolymerized the four pectins into lower-Mw oligosaccharides. All four pectin oligosaccharide products exhibited significant radical scavenging capacities against DPPH, superoxide anion and hydroxyl radicals, demonstrating their effectiveness as natural free radical scavengers. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10068-025-02023-6.