Author:

Abstract:

Water-extractable arabinoxylan (WE-AX) was isolated from rye flour and on average 58% of total rye flour WE-AX could be recovered. The purified WE-AX contained 90.2% AX with an arabinose-to-xylose ratio of 0.53 and an apparent peak molecular weight higher than 1,600,000. The purified WE-AX was fractionated by stepwise ethanol precipitation into different WE-AX fractions (F(0-20%), F(20-30%), F(30-40%), F(40-50%), F(50-60%), F(60-70%), F(70-80%) and F(80+%)). AX was mainly recovered in the F(50-60%) and F(60-70%) fractions and the arabinose-to-xylose ratio of the AX increased with increasing ethanol concentration. Molecular weight, H-NMR and viscosity determinations revealed differences in the structure of the different WE-AX fractions. The purified WE-AX and the ethanol precipitated WE-AX fractions (F(30-40%) – F(70-80%)) were degraded by a glycoside hydrolase family (GHF) 10 Aspergillus aculeatus endoxylanase (XAA), a GHF 11 Bacillus subtilis endoxylanase (XBS) and a GHF 8 Pseudoalteromonas haloplanktis endoxylanase (XPH). The hydrolysis end products were characterised by reducing end sugar residue content, molecular weight and viscosity measurements. The results showed that the enzymic degradability of the rye flour WE-AX fractions is affected by the structural characteristics of the AX and the substrate specificity of the endoxylanase used.