Synthesis, characterization and application of sugar beet pectin-ferulic acid conjugates in the study of lipid, DNA and protein oxidation

In this study, ferulic acid (FA) was enzymatically grafted onto sugar beet pectin (SBP) via laccase catalysis. Structural characterization of sugar beet pectin-ferulic acid conjugates (SFC) with varying substitution degrees was performed using UV–vis, FT-IR, and NMR analyses. Mechanistic analyses revealed that phenolic hydroxyl groups (-OH) on FA reacted with carboxyl groups (-COOH) of SBP via enzymatic catalysis, forming covalent linkages. Additionally, amide bond formation between FA's carboxyl groups and amino groups (-NH₂) of pectin-associated proteins was observed. Compared to unmodified pectin, SFC exhibited reduced crystallinity, lower apparent viscosity, and smoother surfaces, whereas thermal stability and in vitro antioxidant capacity were markedly improved. Notably, SFC with high substitution (>159.60 ± 0.60 mg/g) effectively inhibited malondialdehyde (92.18 %) and peroxide (61.29 %) formation in linoleic acid oxidation systems, while demonstrating DNA (66.07 %) and protein (17.79 %) oxidation inhibition through reduced carbonyl generation. These findings highlight SFC's potential as a multifunctional antioxidant in food and pharmaceutical applications.