Abstract: To understand the dielectric properties of different types of protein in aqueous solutions and further to develop a method for detecting protein adulteration of liquid foods, an open-ended coaxial-line probe was used to explore the changing patterns of the dielectric constant ε’ and dielectric loss factor ε” of aqueous protein solutions (soy protein, whey protein and egg albumin) at a concentration of 0%–4.63% in the frequency range of 20–4 500 MHz at 25 ℃. The results showed that ε’ decreased with increasing frequency, and ε” decreased at first and then increased. At the same protein concentration, the values of ε’ and ε” in soy protein and whey protein solutions had no significant difference, but they were smaller than those in egg albumin at a certain frequency. There were good linear correlations between protein concentration and dielectric properties with a correlation coeffiient of 0.90 and 0.99, respectively. This study indicated that different proteins and their concentration had different influences on dielectric properties of protein solutions, which makes it possible to detect protein types and concentration in protein-based beverage based on dielectric properties.

Key words: soy protein, whey protein, egg albumin, mass fraction, dielectric properties