Hydrothermal Treatment and Enzymatic Hydrolysis of Wheat Bran and Their Effects on Physical Structure

Wheat bran was enzymatically and hydrothermally treated to solubilize the bran. Unlike previous research, in this study, the starch and protein were kept and not removed before the xylanase treatment. This simplified process could be more economical. The retained hydrolyzed protein and starch could provide functional benefits in addition to the arabinoxylan (AX). Wheat bran was hydrolyzed with thermostable α-amylase at 95 °C for 2 h at pH 6.7, protease at 70 °C for 3 h at pH 6.3, and xylanase at 50 °C for 24 h at pH 5.5 as the recommended treatment because of high bran and AX solubilization. The percentage of AX that was solubilized from wheat bran was 50%, and the percentage of AX in the solubles was 23%. The combined solubles had low-, medium-, and high-molecular-weight ranges that corresponded to 152–1012, 1023–8111, and 8111–318 346 g/mol, respectively. A cooking step (>95 °C) followed by xylanase was required before the aleurone structure, comprised of lowly substituted AX and low levels of cellulose, was completely lost and disorganized. The pericarp structure, comprised of highly branched AX and cellulose, was not affected by enzymatic or hydrothermal treatments. X-ray diffraction, small-angle X-ray scattering, solid-state NMR, and light microscopy indicated that hydrothermal and enzymatic treatments did not destroy cellulose crystallinity or disrupt the cell wall polymer organization in the insoluble bran fractions.