Cross-linked Arabinoxylan Research Articles

Potential of dry fractionation of wheat bran for the development of food ingredients, part II: Electrostatic separation of particles

Wheat bran is a composite material made of several layers, such as pericarp, testa and aleurone. It could be fractionated into purified fractions, which might either be used as food ingredients, or serve as a starting material for extraction of bioactive compounds. The aim of this work was to evaluate the potential of using electrostatic separation as a way to obtain purified fractions from wheat bran. Ultrafine-ground bran obtained either by cryogenic grinding or by grinding at ambient temperature was used as starting material. The ultrafine bran was then charged by tribo-electrification and introduced in a chamber containing two high voltage electrodes, where bran particles were separated depending on their acquired charge, allowing positively and negatively charged fractions to be collected separately. The particle size distribution, microstructure and biochemical composition of the obtained fractions were studied. The charge of the particles was influenced by their biochemical composition: particles rich in highly branched and cross-linked arabinoxylans (pericarp) were separated from particles rich in β-glucan, ferulic acid and para-coumaric acid (aleurone cell walls). The testa and the intracellular compounds from aleurone were not highly charged, neither positively nor negatively. The most positively charged fraction represented 34% of the initial bran, and contained 62% of the ferulic acid present in the initial bran. The yield of the separation process was good (5.4% loss), and could be further increased.

Effect of molecular size on physical properties of wheat arabinoxylan

A water-soluble wheat arabinoxylan was fractionated by molecular sieve chromatography into five polysaccharide fractions with limiting viscosities of 8.5 (F1), 6.2 (F2), 4.3 (F3), 3.8 (F4), and 3.4 (F5) dL/g. Compositional, 13C NMR, and 1H NMR analyses revealed very little structural variation among these fractions. The flow behavior of arabinoxylan fractions in dilute and concentrated solutions showed two critical concentrations (c and c). Oxidative gelation of the arabinoxylan fractions, involving intermolecular cross-linking via feruloyl residues, was followed by dynamic rheometry. Almost linear relationships between the storage modulus (G') of the gel network and polymer concentration were found for all fractions. However, while G' values of F1 and F2 increased very rapidly with increasing polymer concentration, F3, F4, and F5 exhibited much less concentration dependence of G'. Positive linear relationships between rigidity (G') of cross-linked arabinoxylan gels and intrinsic viscosity [171 of arabinoxylan fractions were found. The effectiveness of cross-linking reactions, ne(exp)/ne(theor) (ratio of cross-link density experimentally determined to the theoretical value), increased with increasing molecular size of the arabinoxylan fractions. Fractions that formed networks with a high density of cross-linking (F1 and F2) were the most effective in their ability to entrap and hold water. The arabinoxylan fractions were also effective in stabilizing protein foams against thermal disruption in the order F1 > F2 > F3 > F4 > F5.