Study of the application of dielectric spectroscopy to predict the water activity of meat during drying process

Abstract

Drying is considered the most expensive operation because of the time and control required; therefore, it is necessary to optimize this stage of the production process. The measurement of dielectric properties appears to be a promising method for on-line monitoring of the drying process in the meat industry. Permittivity was measured for raw and dried Longissimus dorsi pork samples. The dielectric spectra were measured with an Agilent 85070E open-ended coaxial probe connected to an Agilent E8362B Vector Network Analyser in the frequency range of 500 MHz to 20 GHz. With this technique it was possible to conclude that there is a direct relationship between the dielectric loss factor at 20 GHz, considering the number of water molecules on the surface of sample. It was possible to determine the point of water activity at which the surface temperature reaches the air drying temperature, by using the loss angle at 20 GHz. At this point of water activity, the liquid phase disappears and internal transport controls the drying process. As a result, it was possible to develop a useful tool to predict the surface water activity by using the loss angle at 20 GHz.