Effects of Covalent Binding of Ferulic Acid to Arabinoxylan from Wheat Bran on Its Structure, Antioxidant Activity, and in Vitro Fermentation Properties

This study investigated the effects of covalent binding of ferulic acid (FA) on the structure and bioactivity of arabinoxylan (AX). The AX-FA conjugates were prepared using the N,N’-carbonyldiimidazole (CDI) catalysis method. The degree of FA substitution and AX solubility were measured by the Folin-Ciocalteu method and centrifugal precipitation, respectively. The monosaccharide composition of AX was analyzed via acid hydrolysis combined with GC-MS, while its conformational changes were characterized by HPSEC-MALLS. Antioxidant activity was assessed in Caenorhabditis elegans (C.elegans), and intestinal fermentation characteristics were evaluated using an in vitro pig colon digesta model. The results showed that the CDI method achieved a FA substitution degree of 68.1±0.6 mg/g, while significantly decreased the solubility of AX (P<0.001). The catalysis process did not alter the monosaccharide composition and the conformation of AX, but caused molecular degradation, reducing its molecular weight from 505.9 kDa to 51.83 kDa. Bioactivity analysis indicated that FA binding enhanced the antioxidant activity of AX in C. elegans, increasing the activities of superoxide dismutase (SOD) and catalase (CAT) by 5.2% and 6.7%, respectively, and reducing reactive oxygen species (ROS) levels by 5.7%. Although FA covalent binding partially weakened AX's intestinal health benefits, such as short-chain fatty acid production, the AX-FA complex still promoted the growth of beneficial gut bacteria, including Lactobacillus and Bifidobacterium, while inhibiting harmful bacteria such as Escherichia-Shigella. Thus, compared to FA and AX monomers, the AX-FA covalent complex possesses both antioxidant and probiotic properties. This study provides valuable insights for the preparation and application of polysaccharide-polyphenol conjugates in product development.