The Influence Of Protein Content In Raw Milk On Dielectric Properties

Protein content is the key indicator to measure the quality of milk. Traditional methodsfor detection of milk protein are too time-, cost-and labor-consuming and cannot realizeonline detection. RF/MF dielectric properties, because of its high efficiency, simple and canrealize online detection, have been widely applied in food quality analysis in recent years. Inthis research, with raw milk as the research samples, the influence of protein content on thedielectric properties of raw milk in the RF/MF range (10MHz~4500MHz) was studied, andon this basis, the relation models between protein content and dielectric properties of rawmilk was established. Based on dielectric theories, the correlation mechanism between proteincontent and dielectric properties of raw milk was analyzed as well. The conclusions are asfollows:(1) Within whole test frequency range, the dielectric constants of raw milk weredecreased with increasing temperature, there was a significant nonlinear relationship betweentemperature and the dielectric constants. Within10MHz~800MHz, dielectric loss factorswere increased with increasing temperature. When the frequency was more than800MHz,dielectric loss factors were decreased with increasing temperature. Within whole testfrequency range, there was a significant nonlinear relationship between temperature and thedielectric loss factors. Within whole test frequency range, the dielectric constants of raw milkwere decreased with increasing frequency, the dielectric loss factors were changed fromincrease to decrease with increasing frequency (The turn points were at about2G Hz).(2) Within10~450MHz, the dielectric constants of the raw milk were increased withincreasing whey protein content, when the frequency was more than450MHz, the dielectricconstants were decreased with increasing whey protein content, there was a significant linearrelationship between whey protein content and the dielectric constants. Within whole testfrequency range, the dielectric loss factors were increased with increasing whey proteincontent, there was a significant linear relationship between whey protein content and thedielectric loss factors. Addition of whey protein can increase the interfacial polarization effectand ionic conductivity of milk solution was the main reasons for this phenomenon. (3) Within whole test frequency range, the dielectric constants of raw milk wereincreased with increasing egg protein content, there was a significant linear relationshipbetween egg protein content and the dielectric constants. Within whole test frequency range,the dielectric loss factors were increased with increasing egg protein content, there was asignificant linear relationship between egg protein content and the dielectric loss factors.Within whole test frequency range, Effects of the addition of egg protein on the dielectricproperties of raw milk was greater than whey protein. The main reason for this phenomenonwas: molecular polarity of egg protein was greater than that of whey protein, ionicconductivity of milk solution with added egg protein was gteater than that of whey protein.(4) At frenquency of40MHz, the relation models between whey protein (egg protein)contents and dielectric parameter data of raw milk among test temperatures range achievedthe highest correlation. Model verification result showed the coefficient of determinationbetween predicted values and measured ones was0.996.This research encourages to continue investigations aimed at developing a rapid methodfor the assessment of protein content of raw milk based on measurements of dielectricparameters.