Influence of protein concentration on the physical characteristics and flow properties of milk protein concentrate powders

• As protein content increased, milk protein concentrate powders exhibited altered physical characteristics.
• Increased specific surface area with increasing protein content had a strong negative effect on flowability.
• Increased interstitial air with increasing protein content resulted in powders with high compressibility values.
• High protein powders had poor flowability and significantly different requirements for the design of mass-flow hoppers.

This study investigated the physical characteristics and flow properties of seven milk protein concentrate (MPC) powders, ranging from 36.6 (MPC35) to 89.6 (MPC90) % (w/w) protein in dry-matter. MPC80, MPC85 and MPC90 had the smallest particle sizes (P < 0.05) and significantly higher (P < 0.05) specific surface areas, as measured using nitrogen adsorption. The bulk density of MPC powders decreased with increasing protein content, due to increased (P < 0.05) levels of interstitial and occluded air. Flow testing indicated that high protein MPC powders were more compressible (P < 0.05), had lower flow index values (P < 0.05) and required larger (P < 0.05) outlet diameters for optimal flow in mass-flow hoppers compared to lower protein MPC powders.