Ferulic Acid Content and Appearance Determine the Antioxidant Capacity of Arabinoxylanoligosaccharides

To investigate the antioxidant capacity of ferulic acid (FA) in conjunction with prebiotic arabinoxylanoligosaccharides (AXOS), procedures for the production of FA-enriched, -depleted and cross-linked AXOS were developed, and samples were analyzed using the Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) assays. Results showed that not only the level of FA but also the condition under which it appears (free, bound, or dimerized) impacts the antioxidant capacity of FA-containing AXOS samples. Although esterification of FA on AXOS and cross-linking of AXOS through dehydrodiferulic acid formation lowered the antioxidant capacity of FA by 30 and 55%, respectively, as determined with the TEAC test, the antioxidant capacity of these components still remained high compared to Trolox, a water-soluble vitamin E analog. Total antioxidant capacity of the AXOS samples determined by the ORAC assay resulted in less prominent differences between the different forms of FA than those seen with the TEAC test. Feruloylated AXOS can hence function as strong, water-soluble antioxidants.