Effect of barley and oat β-glucan concentrates on gluten-free rice-based doughs and bread characteristics

The impact of commercial oat or barley β-glucan concentrates incorporated at different levels (1.3–3.9 % actual β-glucan concentration, flour basis) into gluten-free (GF) rice-based dough formulations differing in water content (89–141%, flour basis) on dough rheology (empirical and fundamental tests) and breadmaking performance has been investigated. The effect of the baking process on the content and molecular weight of β-glucan in the final bread has been also evaluated. The rheological properties of the dough were dramatically influenced by dough water content; i.e. optimization of dough hydration is indeed of primary importance on improving GF bread quality. The bread specific volume was negatively correlated with the dough elastic modulus (G′) and the viscosity (η0), and positively with the loss tangent. At optimum hydration, the rheological properties of barley β-glucans-enriched doughs and the quality attributes of breads derived therefrom were notably affected by the soluble fibre content; the G′ at 1 Hz increased up to ∼100% and the bread volume decreased ∼32% with respect to the values of the control dough and bread. In contrast, the impact of concentration of the oat-β-glucan preparation in the fortified doughs and bread was much less pronounced. These findings could be explained by the ability of the low molecular weight barley β-glucans to develop a gel network structure at higher concentrations, whereas the preparation of the high molecular weight oat β-glucan exhibits a more viscous-like rheological response. The added β-glucans to doughs were also quantitated in the bread crumbs, and a significant decrease in their molecular weight was noted, most likely due to the β-glucanase activity in the raw materials incorporated in the GF flour mixtures. Consequently, although the EFSA claims are achievable in gluten-free breads enriched with commercial β-glucans concentrates, control of β-glucanase activity in the raw materials may be a critical issue in exerting all the physiological benefits associated with the consumption of these bioactive polysaccharides.