Water usability: a descriptive parameter of thermodynamic properties and water mobility in glucose/whey protein isolates composite solid matrices

Abstract A classic problem in preservation is the microbes can grow in low-moisture foods. In this paper, the water sorption and thermodynamic properties of glucose/WPI solid matrices were measured, while their molecular mobility was analyzed and associated with the microbial growth of D. Hansenii at various aw and 30 ºC. Although the sorption isotherms, Tg, and relaxation processes of studied matrices were affected by aw and WPI, the microbial growth showed highly dependent on water mobility rather than aw. Hence, we introduced water usability (Uw), derived from the mobility difference between system-involved water and liquid pure water explicating from the classical thermodynamic viewpoint, to describe the dynamic changes of water mobility in glucose/WPI matrices. Despite to aw, the yeast growth rate was enhanced at high Uw matrices concomitantly with a rapid cell doubling time. Therefore, the proposed Uw provides a better understanding of the water relationships of microorganisms in food preservation.