Dielectric Properties of Raw Milk as Functions of Protein Content and Temperature
2015
Zhu, Xinhua | Guo, Wenchuan | Jia, Yunpeng | Kang, Fei
To understand the effect of protein content on dielectric properties (dielectric constant ε ′ and dielectric loss factor ε ″) of raw milk and to provide information for developing protein content detector being suitable for routine laboratory analysis or real-time quality monitoring, the values of ε ′ and ε ″ of raw cow’s milk with the protein content of 3.21–7.12 % were measured over the frequency range from 10 to 4500 MHz at temperatures from 25 to 75 °C by using a vector network analyzer and an open-ended coaxial-line probe. The results showed that the ε ′ decreased with increasing either frequency or temperature. ε ″ decreased linearly with frequency in a log-log plot at low frequency end and had minimums at about 2000–3500 MHz. The minimums increased with temperature. Below about 600 MHz, ε ″ increased with increasing temperature and decreased above 1000 MHz. ε ′ increased linearly with an increase of protein content below about 150 MHz and decreased linearly above 600 MHz, and ε ″ increased linearly with increasing protein content over full investigated frequency range. The developed third-order polynomial models could describe the dielectric properties of raw cow’s milk as functions of protein content and temperature at a given frequency exactly. If the dielectric properties and temperature of milk can be obtained, its protein content could be sensed.
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