Structural, antioxidant, prebiotic and anti-inflammatory properties of pectic oligosaccharides hydrolyzed from okra pectin by Fenton reaction

To elucidate optimum conditions for the production of pectic oligosaccharides (POSs) with excellent antioxidant, prebiotic, and anti-inflammatory activities, okra pectin (OP) was hydrolyzed by Fenton reaction with different concentrations (3 mM, 5 mM, and 7 mM) of FeSO4. Molecular weight of OP was 112.31 kDa. After Fenton reaction with 3 mM, 5 mM, and 7 mM of FeSO4 (products were named as POS3, POS5, and POS7, respectively), molecular weights were significantly reduced to 6.09 kDa, 4.89 kDa, and 1.79 kDa, respectively. This indicates that Fenton reaction is an efficient way to hydrolyze pectin to obtain POSs. Regarding monosaccharide compositions, FT-IR spectra, and NMR spectra ascertained that ·OH produced by Fenton reaction attacked the homogalacturonan region and neutral side chains of rhamnogalacturonan-I. POSs had higher antioxidant activities (DPPH and ABTS radical scavenging activities) than OP due to their lower molecular weights. POSs also increased the number of probiotics (Lactobacillus rhamnosus ATCC 7469 and Bifidobacterium longum ATCC 15707) and promoted generation of SCFAs. Furthermore, POSs with lower molecular weights inhibited LPS-induced nitrite and inflammatory cytokines (including interleukin (IL)-1β and IL-6) as well as inducible nitric oxide synthase (iNOS)/nuclear factor (NF)-κB signaling axis in RAW 264.7 cells. Therefore, it can be concluded that Fenton reaction can successfully prepare POSs having better biological activities than OP. Among three POSs produced, POS7 had the highest antioxidant and anti-inflammatory activities and good prebiotic capacity.