Texture and other changes during storage in model high-protein nutrition bars formulated with modified milk protein concentrates

•Extruded milk protein concentrates (MPC80) produced softer protein bars.•Protein bars made with extruded MPC80 had lower initial sample stress.•Toasted MPC80 performed similar to unmodified MPC80 in protein bars.•Free-amine reduction was slower in protein bars made extruded MPC80.

Extruded or toasted milk protein concentrate with approximately 80 g protein per 100 g were incorporated into model high-protein nutrition bars formulated at 30 g protein per 100 g. The model high-protein nutrition bars also contained other constituents, including glycerol, palm kernel stearin, sugar alcohol syrup, and high-fructose corn syrup, to mimic commercial high-protein nutrition bars. The bars were stored at room temperature (∼22 °C), 32 °C, or 42 °C for up to 42 days. Texture, water activity, and color were measured periodically over the storage period. High-protein nutrition bars formulated with unmodified milk protein concentrate served as the control and maintained similar texture to those high-protein bars formulated with toasted milk protein concentrate. High-protein nutrition bars prepared with milk protein concentrate extruded at 65 °C were significantly softer than the control. Significant differences in hardness and fracturability between high-protein nutrition bars formulated with milk protein concentrate extruded at 120 °C and the control were intermittent over the storage period. Water activity of the high-protein nutrition bars increased slightly during storage, but remained less than 0.65, which assured shelf stability. Surface color change was minimal at 22 °C storage, but increased at 32 °C and 42 °C.