A Study On Measurement Of Milk Component Concentration Based On Infrared Spectroscopy

In the process of milk collection and production control, it is needed to determine the content of the main constituents in milk accurately and rapidly. As the content of fat and protein in milk is the key quality index, most of work on the milk quality determination placed emphasis on the measurement of the two indexes. Routine analytical methods used for milk composition measurement are destructive, expensive, time and labor consuming, and off-line by nature. This paper is concentrated on the application of infrared spectroscopy technique for quantitative analysis of the main constituents in milk, for it is rapid,non-destructive, and environmental friendly.In this paper, the fundamental research on quantitative analysis of fat and protein content in milk is performed by the use of middle infrared spectrum (MIR) and near infrared spectrum (NIR)The method of Attenuate Total Reflection (ATR) was applied to analytical study in MIR. Firstly, an experiment is carried out to get the absorbent attributes of the main constituents in milk. Then mid-infrared spectroscopy analysis technique proved to be suitable to analyze milk components; secondly, a series of factor effects on measurement results are investigated in the application of ATR technology; thirdly, the measurement accuracy of fat and protein content is studied.The following conclusions have been reached, milk has an obvious absorption in the mid-infrared band, and the locations of the absorption peak are consistent with the attributes of molecule functional group analysis and the information from FOSS Company; the effects of the factors on the repeatability (expressed by the value of CV) are below 3‰; For the quantitative analysis, the method of factorial design is applied to optimize the calibration set. The outliers are determined considering the residual variance distribution. The correlations are 0.990 and 0.986 for fat and protein, respectively. The Root Mean of Square Error of Prediction (RMSEP) is 0.121 and 0.111 for fat and protein, respectively. With the application of the methods of wavelengths selection, the numbers of wavelength is decreased greatly from 3301 to 100. The speed is accelerated and the accuracy of the calibration is improved to some extent.The methods of scatter and transmission were applied for investigation in NIR. The characteristics of fat and protein are considered in the analysis of measurement results. The results showed that the method of back scatter is better for the measurement of fat content, and the correlation and RMSEP is 0.994 and 0.097, respectively; the method of transmission is better for the measurement of protein content, and the correlation and RMSEP is 0.980 and 0.130, respectively. Preliminary investigations showed that pretreatment of milk spectral data was an effective method to reduce noise and increase accuracy.The aim of this study was fundamental research on the measurement of milk constituents by the infrared spectroscopy technique. And it laid the foundation for the further investigation.