Dual microwave-ultrasound treatments outperform the single modifications of tef flour. In-depth analysis of physical, hydration, pasting and rheological properties

Abstract

Physical modification of native whole-grain gluten-free flours is an effective strategy to enhance their functionality and industrial applicability. The present study investigated single and dual physical modification of tef flour using microwave (MW) treatment at two moisture contents (MC) (25% and 30%), and ultrasound (US) treatment. The effects of these modifications were assessed through changes in particle morphology, hydration and pasting properties of the flours, and rheological properties of gels and doughs made with them. Both single and dual MW and US treatments significantly altered particle size distribution, with MW inducing agglomeration [D50 = 136 μm (MW25) and 146 μm (MW30)] and US promoting particle fragmentation [D50 = 100 μm (US)], resulting in improved water interactions and increased gel stability. The gels obtained from the dually modified flours exhibited improved solid-like behavior [tan(δ)1 reduction of 8.0% (MW25-US), 13.3% (US-MW25), and 12.6% (US-MW30)] and greater resistance to deformation (λc increase > 200%). Dough rheology revealed that replacing 30% of corn starch with treated tef flour increased the maximum shear stress [τmax up to 14.4 Pa (MW30-US)], reduced tan(δ)₁ (>20% in all dual treatments), and improved recovery capacity [10.0% (US-MW25), 15.1% (US-MW30), 19.9% (MW25-US) and 30.4% (MW30-US)], denoting an enhanced elastic behavior and higher rupture resistance in the dually treated samples compared to the control dough. Principal component analysis, explained 83.15% of total variance, confirmed that MC strongly influenced the extent of modification caused by MW treatment and demonstrated a synergistic effect of dual treatments, particularly when US was applied after MW.