Characterisation of soluble and insoluble cell wall fractions from rye, wheat and hull-less barley endosperm flours

Within cereal endosperm flours, arabinoxylan and beta-glucan molecules exist in either a soluble or an insoluble form. From a nutritional functionality viewpoint, soluble and insoluble forms offer different potential health advantages, so it is important to define both the features controlling solubilisation and the properties of each of the soluble and insoluble fractions. Factors known to affect the stability of arabinoxylan (AX) and beta-glucan (BG) solutions include AX branching extent and type, and the ratio of cellotriose to cellotetraose units (DP3/DP4) in BG. Through studying the solubilisation of AX and BG from wheat, rye, and hull less barley endosperm under conditions that avoid the use of alkali or ethanol during the solubilisation process, we report (a) similar A/X ratios and fine structures for extracted soluble arabinoxylan and the corresponding insoluble AX within the cell walls for rye and wheat endosperm flours, (b) comparable DP3/DP4 ratios for soluble beta-glucan, flour and insoluble beta-glucan within the endosperm cell wall of hull less barley, and (c) evidence for enrichment of beta-glucan at the exterior of residual insoluble cell walls. Therefore, the factors determining solubilisation of AX and BG from endosperm cell walls are different to those that determine the stability of aqueous solutions of the same polymers, and beta-glucan may show limited solubilisation by being trapped within restraining cross-linked arabinoxylans in the cell wall. (C) 2014 Elsevier Ltd. All rights reserved.