Determination of the Fat Content in Cow’s Milk Based on Dielectric Properties

The aim of the work was to obtain a relationship between the dielectric properties (dielectric constant and dielectric loss factor) of milk and its fat content that could be used to develop a rapid and portable milk fat sensor. The dielectric properties of cow’s milk with a fat content of 0.06–4.04 % were measured from 20 to 4500 MHz at 25–45 °C using a network analyzer and an open-ended coaxial-line probe. The results showed that the values of dielectric constant decreased with increasing either frequency or temperature over their investigated ranges. The values of the dielectric loss factor decreased with increasing frequency to minimums at about 2000 MHz and usually decreased as temperature increased at a given frequency. Both dielectric constant and loss factor had negative linear relationship with the fat content at a given frequency below about 2000 MHz and a temperature between 25 and 33 °C, with the coefficients of determination higher than 0.92 and 0.88, respectively. Compared with the measured fat contents using a standard method, the absolute errors of calculated fat contents using obtained dielectric constant and loss factor at 41 MHz and 25 °C were −0.17~+0.18 and −0.24~+0.43 %, respectively. The study indicates that the fat content of cow’s milk could be determined using obtained permittivity values at a frequency and a temperature.