Ultrasonic process affecting interactions between sodium caseinate and whey proteins

Ultrasound has been widely explored for several applications, such as emulsification or structural modification of food materials such as proteins. In this work, the effect of ultrasound on the control of whey proteins (WPI) aggregation was evaluated in the presence of sodium caseinate (NaCas). Solutions of NaCas, WPI and both (1:1) were treated with ultrasound under different power and time conditions and were initially evaluated in terms of particle size distribution, charge density, pH and polyacrylamide gel electrophoresis. Three pairs of conditions were adopted to provide the same energy density -A1 (450 W / 300 s, 6750 MJ/m3), A2 (150 W / 900 s, 6750 MJ/m3), A3 (600 W / 300 s, 900 MJ/m3), A4 (202.5 W / 900 s, 9112.5 MJ/m3), A5 (742.5 W / 300 s, 11137.5 MJ/m3) and A6 (247.5 W / 900 s, 11137.5 MJ/m3). Best conditions of transmitted energy -A1, A3 and A5 -were studied for surface hydrophobicity, circular dichroism and infrared spectroscopy. The decrease of surface hy-drophobicity of NaCas:WPI mixtures pointed to a protective effect of NaCas against WPI denaturation, confirmed by the presence of more ordered structures by FTIR analysis that were not observed in the absence of NaCas. Finally, the effect of these structural changes on the gelation capacity of the ultrasound-treated proteins was assessed. Ultrasound was able to reduce the stress at rupture from 1988.59 Pa (control) to 1655.31 Pa (A3) and 1871.24 Pa (A5), and more markedly increase the Young modulus from 113.69 kPa (control) to 243.30 kPa (A3) and 392.44 kPa (A5). This study identified that higher power values with shorter times were able to provide greater protein changes that affected gelation properties, showing that the modulation of ultrasound conditions can produce ingredients with different techno-functional properties.