Influence of grain particle sizes on the structure of arabinoxylans from brewer's spent grain

Abstract

BSG was milled and sieved and six different grain fractions of different particle sizes (PS) were obtained: PS ≤ 63 μm (PSA); 63 μm < PS ≤ 90 μm (PSB); 90 μm<PS ≤ 125 μm (PSC); 125 μm < PS ≤ 180 μm (PSD); 180 μm<PS ≤250 μm (PSE) and PS>250 μm (PSF). SEM images showed that for the highest particle sizes, cells were still intact while for the smallest particles disruption of cells occurred. The sugar analysis of the grains showed the constant presence of arabinoxylans (AX) and the maximum amount was observed in PSC. AX rich extracts were obtained for all grain fractions presenting different estimate degrees of polymerisation (DP) and degrees of branching (DB). With the decreasing of grain PS, smallest and more branched polymers were extracted; the smallest AX in PSC, and the more branched AX in PSA and PSB. Residual arabinogalactans (AG) were extracted from PSD to PSA. Starch was present in all extracts accounting for 8-10% of the composition of the extract. AX rich extracts with different DP and DB were obtained from different grain PS.

Keywords: Arabinoxylans; Branched arabinoxylans; Brewer's spent grain; Chemical structure; Particle sizes.