Effect of sonication on the viscosity of reconstituted skim milk powder and milk protein concentrate as influenced by solids concentration, temperature and sonication

Skim milk powder (SMP) and milk protein concentrates (MPCs) are manufactured by evaporation followed by spray drying and are widely used as functional and nutritional ingredients. This study investigated the effects of temperature (40-60 °C) and total solids content (TS) on the viscosity of reconstituted MPC (rMPC) (≥30% TS) and SMP (rSMP) (≥46% TS) in laboratory conditions. Additionally, the influence of sonication in batch (70% amplitude) and flow through systems (90% amplitude) was studied in a laboratory setting. The viscosity increased for all treatments with an increase in TS and decreased with an increase in temperature. Overall, sonication in both batch (30 s) and flow through systems (10.1, 20.2, and 30.2 s) resulted in significant decreases in viscosity for both rSMP and rMPC. An increase in viscosity was observed after post-sonication circulation; however, the viscosity did not return to the pre-sonication values.