Comparative Characterization of Oxidative Enzymes for Arabinoxylan and Protein Cross-Linking via Ferulic Acid and Tyrosine in Model Systems

This study comparatively investigated various oxidoreductases (laccase, peroxidase, tyrosinase, and glucose oxidase) and their combinations for their conversion capability of available connection points, tyrosine in proteins and ferulic acid (FA) in arabinoxylans, as useful cross-linking tools. Therefore, substrate specificity and pH- and temperature-dependent activity were studied in different substrate ratios. Enzyme characteristics varied notably across standard assays, where even substrate-dependent shifts in pH optima occurred. Combining enzymes significantly reduced the <i>K</i>_m for laccase with tyrosinase (0.504 to 0.238 mM) for tyrosine, whereas for FA, the <i>K</i>_m increased from 0.057 to 0.107 mM but decreased for peroxidase with glucose oxidase from 0.250 to 0.045 mM. The substrate ratio was found to be crucial to target homo- or heterocross-linking and the most effective simultaneous substrate conversion was reached by combining peroxidase with glucose oxidase at a 1:5 (FA:tyrosine) ratio. These outcomes provide valuable insights into the cross-linking behavior of oxidoreductases, supporting a rational selection for food structure improvements.