Enzymatic oxidative treatments of wheat bran layers: Effects on ferulic acid composition and mechanical properties

Enzymatic treatments known to induce the gelation of feruloylated arabinoxylans solutions were applied to tissue strips isolated from peripheral layers of wheat grain to tentatively produce in situ arabinoxylan reticulation. The treatments by horseradish peroxidase (HRP) and manganese dependent peroxidase (MnP) induced a dimerization of ferulic acid (FA) in wheat bran with concomitant decrease of arabinoxylan solubility. Similar results were obtained, but to a lesser extent, by simple incubation of bran strips in water, suggesting the action of endogenous peroxidases. The fact that these treatments proved to be ineffective on the isolated aleurone layer and pericarp suggested that dimerization occurred mostly at the aleurone-pericarp interface. In addition, the MnP system generated a consumption of monomer and dimer of ferulic acid in the pericarp, perhaps due to their incorporation into lignin. Micro-mechanical tests using DMTA were performed on isolated tissue strips and showed that oxidation of wheat bran increased their mechanical strength (increase of stress and strain to rupture).