Treatments with Xylanase at High (90 %) and Low (40 %) Water Content Have Different Impacts on Physicochemical Properties of Wheat Bran

Abstract

The aim of the work was to elucidate the impacts of treatment with xylanase at high (90 %) and low (40 %) water contents on the structural and physicochemical properties of wheat bran. The bran treatments at 40 % water content, both with and without added xylanase, resulted in a smaller average bran particle size, more changes in bran microstructure, and higher solubilization of polysaccharides than the corresponding treatments at 90 %. Also, the water holding capacity of bran (3.6 ± 0.1 g water/g bran dm), determined by Baumann method, decreased more already after 4-h xylanase treatments at 40 % (2.4 ± 0.1) than at 90 % (2.9 ± 0.2). The solubility of salt-extractable bran proteins decreased during the treatments, especially at 40 %, also without added xylanase. Protein aggregation was detected in the SDS + DTT-extractable bran fraction, which also contained small proteins of 10–20 kDa not detectable in the untreated bran. The use of xylanase had only minor effect on bran proteins as compared to the treatments without added xylanase. The results indicate the large role of mechanical shear on the bran properties at 40 % water content. The low arabinose/xylose ratio (0.32) in the bran water extract after 24-h xylanase treatment at 40 %, however, suggests that the solubilization of arabinoxylan was caused by enzymatic action, and not by mechanical degradation. Arabinose/xylose ratio of the bran water extract decreased similarly during all the treatments, suggesting similar solubilization pattern of arabinoxylan at both water contents. The study showed that bran properties can be significantly modified by adjusting the water content and mechanical energy used in processing.