Journal of Food Engineering, Vol.149, 105-113, 2015
Rehydration characteristics of milk protein concentrate powders
Low-(MPC35, MPC50), medium-(MPC60, MPC70) and high-(MPC80, MPC85, MPC90) protein content milk protein concentrate (MPC) powders, manufactured at pilot-scale, were evaluated for their rehydration characteristics. Optical tensiometry confirmed that water droplets were imbibed more slowly as protein content of the MPCs increased, indicating impaired wetting. Casein micelles comprised only <2% of the particle population by volume in MPC70, MPC80, MPC85 or MPC90 after 90 mm of rehydration at 25 degrees C, as primary particles which had not dispersed fully remained in suspension. The quantity of sediment, measured using analytical centrifugation, increased in the order MPC70 < MPC80 < MPC85 < MPC90 after 90 mm of rehydration at 25 degrees C, with lower protein MPCs forming no sediment. No sediment formation was observed in any of the MPCs after 24 h of rehydration at 25 degrees C, despite the predominance of primary particles in suspensions of high-protein MPCs. Increasing the temperature of reconstitution from 25 to 50 degrees C during 90 mm of rehydration caused a 41.4% decrease in sediment height for MPC90 in water; however, reductions in sediment height of 89.9% and 99.5% were achieved when MPC90 was rehydrated in milk permeate or 80 mM KCl, respectively. It is evident that low ionic strength (confirmed using conductimetry) has a strong negative effect on the rehydration properties of high-protein MPCs, and that the synergistic effect of increasing ionic strength and temperature can substantially accelerate rehydration. (C) 2014 Elsevier Ltd. All rights reserved.