Impact of ferulic and vanillic acids on soluble and insoluble dietary fiber utilization from maize bran by the human gut microbiota†

Ferulic (FA) and vanillic (VA) acids are phenolic compounds with antioxidant activity and health benefits. Our previous research indicated that the utilization of maize dietary fiber by the human gut microbiota might be negatively impacted by phenolic compounds. This study investigated the effects of FA and VA at different concentrations (0, 0.3, 3, 30 mg g⁻¹) on soluble and insoluble maize bran fibers during in vitro fecal fermentation. High VA (30 mg g⁻¹) reduced insoluble fiber utilization (p = 0.016), increased branched-chain fatty acid production (p = 0.024), and was associated with increased Veillonellaceae and Bacteroidaceae abundances. Low FA (0.3 mg g⁻¹) improved soluble fiber utilization (p = 0.017) and enhanced propionate production (p = 0.013). High FA (30 mg g⁻¹) elevated propionate (p = 0.015) and butyrate (p = 0.004) production. FA and VA reduced Streptococcaceae and Peptostreptococcaceae abundances. These findings highlight the complex interplay between phenolic compounds and dietary fiber utilization with implications for dietary strategies promoting gut health.