Influence of dairy proteins on textural changes in high-protein bars

The effects of milk protein type, formulation and storage were investigated in model bar systems to gain improved insight into deteriorative, textural changes. Texture analysis, water activity measurements, confocal laser scanning microscopy and Fourier transform infrared (FT-IR) spectroscopy were used to monitor interactive physical and chemical changes in bars during storage. Hardness of bars was dependent on protein type, concentration and co-solvents. Microstructural changes in bars during elevated temperature storage showed swelling and fusion of powder particles. FT-IR spectra suggest a molecular contribution to hardening due to solvent-induced plasticisation and reconformation of protein secondary structures. Hardness development in high-protein bars appears to result from non-equilibrium changes due to the hydration behaviour of individual components and the competition for available moisture. Minimisation of water activity differences between ingredients provides a means of controlling hardness. The work provides improved understanding of textural changes in highly-concentrated food systems.