Migration of small molecules and its effect on texture hardening in high- protein nutritious bars made of WPI during early storage

High- protein nutritious bars are suffering from texture hardening,which limits their shelf life. The mechanisms for the hardening of high- protein nutritious bars are rather complicated.In this research,protein bar model systems were prepared with WPI,water,and glycerol.By adjusting the proportion of water and glycerol in the solvent fraction,a series of models with different storage stability were obtained. Texture analyzer,confocal laser scanning microscope,and low- field nuclear magnetic resonance were used to investigate the relationship between migration of small molecules and texture hardening of the systems in the early stage of storage.It was suggested that the changes in texture of the model system converted from“keeping constant”to“hardening rapidly”as the proportion of glycerol in solvent increased. WPI- water system formed a uniform structure without undissolved protein particles.Migration of small molecules or change of microstructure was not observed and the system kept soft during the early stage of storage. However,as the proportion of glycerol was increased,undissolved protein particles could be observed and the small molecules such as glycerol and water migrated into the particles during the storage,which caused texture hardening. In conclusion,the migration of small molecules was a key factor for the rapid hardening of high- protein nutrition bars in the early stage of storage.