Effects of particle size and aging of milk protein concentrate on the biophysical properties of an intermediate-moisture model food system.

This study investigates the effects of particle size (22.4 and 7.5 μm diameters) and aging history (40 °C, 20 days) of milk protein concentrate (MPC) powders on their rehydration properties as well as the biophysical properties including molecular migration, microstructure, and texture of a high-protein nutrition bar (HPNB) made using these MPC powders. It was observed that the rehydration properties (wettability and solubility) of MPC powders decreased with aging but increased with the decrease in the MPC particle sizes. The migration of small molecules (water, glycerol and sorbitol) was slower for HPNB formulated with aged powders of the same sizes but faster for those formulated with small-sized powders of the same aging history. Plasticization of powder particles was lesser for HPNB formulated with aged powders having the same sizes, but greater for those formulated with small-sized powders with the same aging history. The increase in hardness during storage was smaller for HPNB formulated with fresh and small-sized powders, compared to those formulated with aged and large-sized powders. The cohesiveness was higher for HPNB formulated with small-sized powders, compared to those formulated with large-sized powders. These results suggest that the reduction of the MPC powder particle size by manipulating the spray airflow rate offers a potential route to manipulate the textural properties of HPNB. • MPC powder rehydration decreased with aging and with particle size increase. • Molecular migration was faster for HPNB containing small MPC particle size. • Plasticization of particle was greater for HPNB containing small MPC particle size. • Hardness increase with storage was smaller for HPNB with small MPC particle size. • Cohesiveness was higher for HPNB containing small MPC particle size. [ABSTRACT FROM AUTHOR]