Dielectric properties of raw milk as influenced by frequency, salts, and salt contents

Abstract

AbstractTo understand the effect of salts and salt contents on dielectric properties (dielectric constant ε′ and dielectric loss factor ε″) of milk, dielectric properties of raw cow's milk samples at the total salt content (in mass) of 0.75–0.87%, 0.75–0.93%, and 0.75–0.90% by adding NaCl, MgCl2, and KCl, respectively, were obtained from 19 to 3,000 MHz at 25 °C using an impedance analyzer. The results showed that ε′ decreased with increasing frequency, and ε″ changed with “V” shape and had minimums at about 1,500 MHz. At a given frequency and the same salt addition level in molar, the milk added with NaCl and MgCl2 had the smallest and the biggest ε″, respectively. At about 40 MHz, ε′ had a very good positive linear relationship with the total salt content of milk, whose coefficients of determination were 0.96, 0.98, and 0.95 for NaCl, MgCl2, and KCl, respectively. ε″ increased linearly with increasing total salt contents with the coefficients of determination higher than 0.99 below about 900 MHz and higher than 0.86 above 900 MHz no matter for which salt.Practical applicationsThis work shows that there were linear relationships between dielectric properties and total salt contents. The study is helpful to understand the influence of salts and salt content on dielectric properties of raw cow's milk, and it offers useful information for developing portable salt detector based on dielectric properties in the future.