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| Purpose: The purpose of this reported research was to use the thermodynamic property based theoretical approach of strong electrolyte aqueous solutions to calculate the water activity of selected saturated salt solutions at 15C and 35C. |
| Abstract: A theoretical approach was used to predict the water activity (aw) at 15C and 35C of selected saturated salt solutions used as standards in the range of microbial growth (~0.57-0.97). For this purpose a rigorous thermodynamic model to predict osmotic coefficient was used. The results agreed very well with experimental measurements at 15C and 35C for most salts studied, which included NaBr, NaCl, (NH4)2SO4, KCl, BaCl2, and K2SO4. For KNO3 the agreement at the higher temperature was somewhat less satisfactory and the reasons for this behavior are discussed. |
| Experimental: Water activity was measured using a Novasina Humidat-TH2 Thermoconstanter hygrometer. It was determined that the theoretical preductions could be used to determine the microbiological quality control needs in a food. The approach in this paper may help to find ways to reach a general agreement on the aw of standards used to calibrate aw measuring devices. |
The aw of NaCl and KCl saturated solutions between 15C and 37C.[modified]
| TEMPERATURE,C | NaCL | KCl |
| 15 | 0.753 | 0.859 |
| 17 | 0.753 | 0.856 |
| 19 | 0.752 | 0.852 |
| 21 | 0.752 | 0.849 |
| 23 | 0.751 | 0.846 |
| 25 | 0.751 | 0.842 |
| 27 | 0.750 | 0.840 |
| 29 | 0.750 | 0.836 |
| 31 | 0.750 | 0.833 |
| 33 | 0.749 | 0.830 |
| 35 | 0.749 | 0.827 |
| 37 | 0.748 | 0.823 |
Unsaturated NaCl solutions used as isopiestic standards for calibration of the Novasina Thermoconstanter hygrometer at 15 C and 35C [modified].
| Concentration %(w/w) | Aw (15C) | Aw (35C) |
| 23.50 | 0.795 | 0.795 |
| 22.50 | 0.808 | 0.808 |
| 21.50 | 0.821 | 0.821 |
| 20.50 | 0.833 | 0.833 |
| 19.02 | 0.852 | 0.850 |
| 18.38 | 0.859 | 0.857 |
| 17.70 | 0.867 | 0.864 |
| 17.01 | 0.874 | 0.872 |
| 15.25 | 0.891 | 0.889 |
| 13.42 | 0.908 | 0.906 |
| 11.98 | 0.921 | 0.920 |
| 10.71 | 0.930 | 0.929 |
| 8.25 | 0.949 | 0.948 |
| 6.18 | 0.963 | 0.962 |
| 2.44 | 0.986 | 0.986 |
Updated: Thursday, September 6, 2007.
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