Effect of retentate heat treatment and spray dryer inlet temperature on the properties of milk protein concentrates (MPCs)

High protein (>80%) milk protein concentrates (MPCs) dried under mild conditions were utilized to determine if preheat treatment would affect the particle size characteristics of MPC. Increasing the preheat treatment from 72degreesC to 76degreesC and 80degreesC caused a change in viscosity of 26 and 60% as compared to the retentate heated to 72degreesC. Increasing the preheat treatment from 72 to 76degreesC had no significant effect on the volume weighted particle size D[4,3] or mean particle size D[0.5], but it resulted in increased surface weighted particle size D[3,2] and decreased surface area. The ease of dissociation of hydrated particles with ultrasonication and beta-mercaptoethanol was least for the MPC in which the retentate had been pre-heat treated above 72 degreesC. Medium protein (similar to 70%) MPCs dried under more severe outlet conditions were utilized to determine the effect of varying the inlet temperature from 200 to 250 and 300 degreesC on particle size distribution characteristics of the MPCs. Increasing the inlet temperature caused an increase in the volume weighted particle size D[4,3] and mean particle size D[0.5], with the effect on the surface weighted particle size D[3,2]. Specific surface area were only changed for the samples dried at 250degreesC as compared to those dried at 200degreesC. The ease of dissociation of the hydrated particles was significantly decreased as the inlet temperature was decreased as noted by all 4 particle size characteristics.