Effect of lactose content on dielectric properties of whole milk and skim milk

Dielectric properties (dielectric constant epsilon and dielectric loss factor epsilon) of whole milk and skim milk with the lactose content of 4.56-6.44% and 4.57-6.47%, respectively, were measured over the frequency range of 20-4500 MHz at 25 degrees C using a vector network analyzer. The results showed that epsilon decreased with increasing frequency, and epsilon changed with V shape and its minimum was noted at about 2000 MHz. Whole milk had lower dielectric properties than skim milk at almost same lactose content and a given frequency. epsilon had weak positive linear relationship with lactose content for whole milk, but had negative linear relationship for skim milk. No matter for which milk, epsilon had very good negative linear relationship with lactose content below 1000 MHz and had good positive linear relationship above 2300 MHz. The study provides information on developing rapid lactose detector for milk in future.