Molecular migration in high-protein intermediate-moisture foods during the early stage of storage: Variations between dairy and soy proteins and effects on texture

Effect of molecule migration on the hardening of high-protein intermediate-moisture foods (HPIMF) in the early stage of storage was investigated through low-field NMR, texture analysis, confocal laser scanning microscopy, scanning electron microscopy, and protein solubility analysis. Model systems were made of water, glycerol and sorbitol, together with sodium caseinate (NaCN), soy protein isolate (SPI) or whey protein isolate (WPI), and stored at 25 °C to monitor molecular migration and the changes of texture, microstructure, and protein solubility. Both yield strain and yield stress of NaCN and SPI systems increased rapidly right after preparation, together with decreases in small molecules mobility and changes of microstructure, while WPI system showed more uniform structure without significant change of small molecules mobility. In addition, changes in protein solubility were observed in the SPI systems, but not in NaCN and WPI systems. These results suggested that the migration of small molecules (water, glycerol, and sorbitol) into protein particles during the early stage of storage could reduce the mobility of small molecules and might cause changes in microstructure, which could further cause hardening of HPIMF. In addition, the variation in protein sources was also a major factor contributing to the difference in texture properties.