Milk protein concentrates with more than 80% protein (that is, MPC80) are underutilized as the primary protein source in high‐protein nutrition bars as they impart crumbliness and cause hardening during storage. High‐protein nutrition bar texture changes are often associated with internal protein aggregations and macronutrient phase separation. These changes were investigated in model high‐protein nutrition bars formulated with MPC80 and physically modified MPC80s. High‐protein nutrition bars formulated with extruded MPC80s hardened slower than those formulated with toasted or unmodified MPC80. Extruded MPC80 had reduced free sulfhydryl group exposure, whereas measurable increases were seen in the toasted MPC80. High‐protein nutrition bar textural performance may be related to the number of exposed free sulfhydryl groups in MPC80. Protein aggregations resulting from ingredient modification and high‐protein nutrition bar storage were studied with sodium dodecyl sulfate polyacrylamide gel electrophoresis. Disulfide‐based protein aggregations and changes in free sulfhydryl concentration were not consistently relatable to high‐protein nutrition bar texture change. However, the high‐protein nutrition bars formulated with extruded MPC80 were less prone to phase separations, as depicted by confocal laser scanning microscopy, and underwent less texture change during storage than those formulated with toasted or unmodified MPC80.