Dissolution of Wheat Bran by NaOH/Urea Solutions and Structure of Soluble Materials

Abstract

Wheat bran is an abundant low-cost byproduct of the wheat milling industry that can be used as a renewable resource for the production of biofuels, chemicals, feed, and food ingredients. In this study, destarched and deproteinized wheat bran (DSDPB) was treated with a mixture of either 7 or 9% sodium hydroxide and 12% urea solvent, and the structure of the extracted polymers was investigated. Three and 6 cycle dissolution schemes were examined involving the repeated cooling of the solvent bran mixture to −12.6 °C and then agitating it at 25 °C. When 7% NaOH/12% urea (6 cycle) was applied to DSDPB, 84.1% of the material was solubilized including 89.8% of the arabinoxylans (AX). The high molecular weight fraction constituted 62.9% of the AX originally in the DSDPB. This procedure recovered more wheat bran arabinoxylans for characterization than any previous study using alkaline dissolution. The percent solubilization and its molecular weight significantly increased with more dissolution cycles. The material insoluble in NaOH/urea contained crystalline cellulose, which may have provided the cell wall with structure, along with cross-links, to prevent complete solubilization. Enzymatic treatment of the high molecular weight fraction provided evidence of carbohydrate–protein conjugation.