High-protein nutrition bars and other shelf-stable, intermediate moisture foods often harden to unpalatable levels during storage; however, a new study published in the Journal of Food Science suggests adding ground extruded milk protein concentrates (MPC) with 80 percent protein can enhance the texture and other sensory attributes of high-protein nutrition bars.

Previous instrumental study of high-protein nutrition bars formulated with extruded MPC indicated slower hardening compared to bars formulated with unmodified MPC. However, hardness, and its change during storage, insufficiently characterizes high-protein nutrition bar texture.

For the study conducted by researchers at Iowa State University, MPC80 was extruded at two different conditions and model high-protein nutrition bars were prepared. A trained sensory panel and instrumental techniques were used to measure high-protein nutrition bars firmness, crumbliness, fracturability, hardness, cohesiveness and other attributes to characterize texture change during storage.

The researcher found extrusion modification, storage temperature and storage time significantly affected the instrumental and sensory panel measured texture attributes. The high-protein nutrition bars became firmer and less cohesive during storage. When evaluated at the same storage conditions, the texture attributes of the high-protein nutrition bars formulated with the different extrudates did not differ significantly from each other; however, textural differences were noted most of the time between the control and the high-protein nutrition bars formulated with extruded MPC80. An adapted high-protein nutrition bars crumbliness measurement technique produced results that were correlated with sensory panel measured crumbliness (r = 0.85) and cohesiveness (r = -0.84). Overall, the high-protein nutrition bars formulated with extruded MPC80 were significantly softer, less crumbly and more cohesive than the control during storage.

The researchers concluded extruding milk protein concentrate with 80 percent protein produced a functional ingredient that, when incorporated in high-protein nutrition bars, resulted in favorable texture attributes, for example, reduced firmness and improved cohesiveness, when compared to the unmodified control.