β-Lactoglobulin–sodium alginate interaction as affected by polysaccharide depolymerization using high intensity ultrasound

The purpose of this study was to provide insights into the interaction between β-lactoglobulin (BLG) and sodium alginate (ALG, before and after sonication) using isothermal titration calorimetry (ITC), streaming current detector (SCD), turbidity measurement, dynamic light scattering and electrophoretic mobility methods. High intensity ultrasound could effectively decrease the intrinsic viscosity of the ALG solution. Time and amplitude of the sonication treatment had a direct effect on the viscosity depression, while the sonication temperature had an inverse effect. ITC measurements indicated that the sonication decreased the interaction strength between ALG and BLG. The isoenthalpic plateau was obtained at higher ALG (US)/BLG weight ratio compared to ALG (IN)/BLG weight ratio. The zeta-potential of the nanoparticles produced from ALG (US)–BLG attractive interaction was lower than of those produced from ALG (IN)–BLG interaction. These differences were attributed to the lower charge density of the ALG (US) as a result of sonochemical interactions. Particle size measurements showed that the effect of the sonication treatment was the homogenization of the nanoparticles in the mixed dispersion. The biopolymeric nanoparticles formed may therefore be useful as a delivery system for fortification purposes of transparent liquid food products.

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► Sonication decreased the viscosity of the sodium alginate solution.
► Alginate sonication reduced its interaction strength with β-lactoglobulin.
►  Sonication downsized nanoparticles formed in the mixed dispersion with protein.