Low-frequency ultrasonication modulates the impact of annealing on physicochemical and functional properties of rice flour

Ultrasonication (US) is a green technology used to physically modify flours to increase their industrial range of applicability. The aim of this work was to study the combined effect that dual US and annealing (ANN) treatments have on starch and protein structure of rice flour, at 20, 40, 50 and 60 °C. Results showed clear modifications of functional, thermal and pasting properties of flours, as well as rheological properties of gels made from them. US + ANN led to generation of small-size particles, which markedly increased the swelling power and starch damage. X-Ray Diffraction and FTIR indicated that starch crystallinity and protein secondary structure was affected by the shear forces of cavitation. The combination of US + ANN improved the crystalline structure arrangement within the starch granules, causing narrowing of the gelatinization temperature range (ΔT). Pasting viscosities were significantly decreased by ultrasonication, following an increasing trend with increasing temperature, while pasting temperature was increased, agreeing in the achievement of a thermodynamically more stable structure. The rheological properties indicated a reduction of the elastic (G′) and viscous (G″) moduli after ultrasonication, as well as lower values of tan (δ), reflecting a higher predominance of elastic modulus versus viscous one than the non-sonicated flours. The rice flour's properties were found to be highly sensitive to the applied treatment conditions, showing a synergetic effect when sonicating at the highest studied temperature.