Extraction by three processes of arabinoxylans from wheat bran and characterization of the fractions obtained

Abstract

Arabinoxylans (AXs) were extracted from destarched wheat bran (DWB) according to different processes, with a view to their production at industrial scale. Two fractions (F3a and F3b, respectively, purified on 10kDa and 100kDa ultrafiltration membranes) were obtained with low yields by treating DWB with an endoxylanase and this process left a solid residue exhausted in enzyme-extractable AXs (EDWB). F1 and F2 AX fractions were obtained by treatment with sodium hydroxide of, respectively, DWB and EDWB. The fraction F4 resulted from a hydrothermal treatment of EDWB in a pressure reactor, followed by ethanol precipitation. The different AX fractions were characterized and compared for the composition in monosaccharides, for the contents in fats and in ferulic, phytic and uronic acids, for the molecular mass distribution and the degrees of methylation and acetylation. The alkaline extractions gave one deesterified AX population with molecular mass (MM) higher than 670kDa and arabinose/xylose ratios (Ara/Xyl) around 1. The enzyme and thermal treatments yielded AXs with two main populations in size-exclusion chromatography (the largest one at 5–12.5kDa and a second one at 140–160kDa), having overall Ara/Xyl of, respectively, 0.7 and 0.5 for both processes. These data bring information about the influence of the process on the characteristics of AX fractions obtained from pretreated wheat bran. Here are also reported processes that enabled to recover enzyme-unextractable AXs from DWB, including an original and up-scalable hydrothermal extraction. Phytate contents of isolated AXs are described for the first time.