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

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.