Microorganisms require water for their metabolic activities. Only a fraction of water in foodstuffs, the so-called “free water”, is available for this purpose. The amounts of “free” water previously estimated by two different methods [J. Phys. Chem. A 114 (2010), 11933–11942; J. Phys. Chem. A 155 (2011), 4563–4563; Journal de Recherches Atmosphériques 4 (1969), 65–78] are compared for aqueous solutions of four electrolytes, NaCl, NH4Cl, Na2SO4, (NH4)2SO4: (i) Vapour pressure measurements of the solutions relative to that of pure water (water activities). (ii) Low-wavenumber Raman spectra in the R(ν)-representation. For each electrolyte deviations were found between results from the two methods. All water molecules in the illuminated volume contribute to the Raman data. The vapor pressure measurements refer to water molecules at the water/atmosphere interface where surface tension is important. Differences in surface tension for the four electrolytes qualitatively explain deviations between the amounts of “free water” observed by the two methods.
IOS Press, Inc.
6751 Tepper Drive
Clifton, VA 20124
Tel.: +1 703 830 6300
Fax: +1 703 830 2300 email@example.com
(Corporate matters and books only) IOS Press c/o Accucoms US, Inc.
For North America Sales and Customer Service
West Point Commons
Lansdale PA 19446
Tel.: +1 866 855 8967
Fax: +1 215 660 5042 firstname.lastname@example.org