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

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 a w and 30 ºC. Although the sorption isotherms, T g , and relaxation processes of studied matrices were affected by a w and WPI , the microbial growth showed highly dependent on water mobility rather than a w . Hence, we introduced water usability ( U w ), 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 a w , the yeast growth rate was enhanced at high U w matrices concomitantly with a rapid cell doubling time. Therefore, the proposed U w provides a better understanding of the water relationships of microorganisms in food preservation.