Molecular basis of water activity in glycerol-water mixtures

Nakagawa, Hiroshi   ; Oyama, Taiji*

Water activity is thermodynamic value defined as the ratio of the equilibrated vapor pressure of the sample to the vapor pressure of pure water at the same temperature. It is known that this value is a reliable indication of the microbial growth, enzymatic activity, and preservation and quality of foods. However, a molecular basis of water activity is still under debate in the related multiple area. Glycerol-water mixtures can provide the variation of water activities by controlling the ratio of glycerol and water. In this study, molecular basis of water activity was examined by using differential scanning calorimetry, attenuated total reflection Fourier-transform infrared spectroscopy and incoherent quasi-elastic neutron scattering based on isotherm sorption curve of glycerol-water mixtures. We found that diffusive dynamics of water is correlated with hydrogen bond related local vibrational dynamics in the glycerol-water mixtures. More importantly, water activity of glycerol-water mixtures can be explained by the hydrogen boding network and molecular dynamics of water in the solutions.