Effect Of Homogenization On Dielectric Spectroscopy And Prediction Accuracy Of Main Components Of Raw Milk

Raw milk is raw material of dairy products.Quality testing of raw milk is important to ensure the quality and safety of dairy products.The traditional detection method for milk component has the disadvantages of time-consuming,laborious operation and process complexity,which cannot meet the requirements of rapid detection.However,rapid,accurate and convenient detection of component content of raw milk is the focus of research on dairy detection technology.Dielectric spectroscopy has the advantages of fast detection,and suitable for on-line or on-site detection,which is of great significance for the rapid detection of milk components.Homogenization is an important part of processing of raw dairy products.However,effect of homogenization on physical and chemical properties of milk is not clear,and influence of homogenization on the detection of dielectric spectroscopy has not been studied.Therefore,raw milk and homogeneous milk under different homogeneous conditions were studied in this paper,and effect of homogenization treatment on the particle size distribution parameters of milk was studied.Dielectric properties of raw milk and homogeneous milk were studied based on RF/microwave dielectric spectroscopy.The quantitative prediction models of protein,fat and solids-not-fat content of raw milk and homogeneous milk were established,respectively,and the results of the prediction model were compared.The methods to improve the accuracy of model prediction based on dielectric spectroscopy were proposed,which provided a research basis for the development of raw milk quality detector based on dielectric spectroscopy.The main contents and conclusions of this paper are as follows:(1)When the homogenization inlet temperature was 25°C and second-stage pressure was the same,the particle size distribution parameters of milk decreased with increasing first-stage homogenization pressure,and raw milk had largest value under the same particle size parameter.Effect of Two-stage homogenization was better than one-stage homogenization,but the second-stage pressure had little effect on the particle size distribution parameters.Under the same homogenization pressure,the particle size distribution parameter value of the homogenization inlet temperature of 50°C of milk was smaller than homogenization inlet temperature of 25°C.(2)The dielectric constant(?')and loss factor(?")of milk with homogenization inlet temperature of 25°C generally increased with increasing homogenization pressure at any selected frequency over the frequency range of 20 ~ 4500 MHz.When the first-stage homogenization pressure was 0~40MPa and the second-stage pressure is 5MPa,the ?' and ?" of the milk increased with increasing first-stage homogenization pressure.What's more,the ?' and ?" of raw milk and homogeneous milk of first-stage homogenization pressure was 70 MPa and second-stage homogenization pressure was 5MPa had the minimum value and the maximum value,respectively.(3)Under the same homogenization pressure,the ?' and ? " of milk with homogeneous inlet temperature of 50°C was larger than that of milk with homogeneous inlet temperature of 25°C.The ?' and ?" of milk with homogeneous inlet temperature of 50°C didn't change significantly with change of the homogenization pressure.However,they were obviously greater than ?' and ? " of raw milk.When homogenization inlet temperature was higher than 40°C,fat viscosity and fat particles in milk were smaller,and the degree of dipole orientation was higher and the ionic conductivity was larger,resulting in larger value of ?' and ?" of milk with homogeneous inlet temperature of 50°C.(4)The Residual Predictive Deviation(RPD)of the optimal model for protein,fat and solids-not-fat of raw milk based on dielectric spectroscopy was 1.613,1.883 and 1.594,respectively,while the RPD of protein,fat and solids-not-fat of homogeneous milk was 2.278,2.149 and 1.748,respectively.The results of dielectric spectroscopy prediction model of homogeneous milk were better than that of raw milk,indicating that homogenization treatment could improve prediction accuracy of milk composition.(5)Homogenization had some effects on the dielectric spectroscopy of milk and the improvement of component prediction accuracy based on dielectric spectroscopy.The study found that milk sample was heated to 40°C and processed by ultrasonic treatment instead of manually stirring,which helped to improve the repeatability of dielectric spectroscopy of raw milk.This study provided theoretical basis and technical support for the development of detectors for detecting the main quality parameters of milk in real time or on-line based on dielectric spectroscopy.