Effect of power ultrasound pre-treatment on the physical and functional properties of reconstituted milk protein concentrate

This work investigated the impact of power ultrasound (PUS) pretreatment on the physical and functional properties of reconstituted milk protein concentrate (MPC) 80. Ultrafiltered/diafiltered (UF/DF) milk protein retentates were treated with PUS (12.50 +/- 0.31 W and 50% amplitude) for 0.5, 1, 2, and 5 min prior to spray drying. Results revealed that the particle size (D50) reduced from 28.45 mu m to 0.13 mu m after 0.5 min of sonication. Solubility increased significantly from 35.78% to 88.30% after 5 min of PUS pre-treatment. Moreover, the emulsifying activity index (EAI) of MPC samples increased significantly as the time of ultrasonic treatment was prolonged. Additionally, the emulsion stability index (ESI) initially increased after ultrasound treatment for 1 min. Surface hydrophobicity was greatly increased with more hydrophobic groups exposed to the environment. PUS pre-treatment also promoted an increase in the storage modulus (G') of the MPC solutions. Viscosity significantly decreased after PUS pre-treatment. This result was confirmed by the microstructure of the powder, with small particles formed and trapped in dents of large particles. However, sodium-dodecyl sulfate-polyacrylamide gel electrophoresis showed no significant change in protein molecular weight. (C) 2013 Elsevier Ltd. All rights reserved.