Study On Mechanism And Influence Factors Of Optical Measurement Of Milk Quality

Optical measurement techniques are advantageous and potential for monitoring the quality of milk. However, near-infrared spectroscopy hasn't been applied in production. The main reasons lie in the lack of study on the"milk optics". The thesis focuses on the research of the mechanism and influence factors of optical monitoring the quality of milk. The reasons of low measurement precision of current near-infrared optical methods are analyzed comprehensively, and the limitations of some key issues are made clear. The optical model based on the interaction between optic and milk is established, which solves the theoretical problems. The influence of temperature and homogenization on the measurement of milk composition is studied, and the solutions are presented, which settle the difficulties and limitations of the optical measurement techniques for the practical application.From the measurement theory and process, the application of the current near-infrared optical methods on the monitoring the quality of milk is analyzed systemically and then the rationality and limitations are indicated. The application of the current optical methods is performed in the whole near-infrared regions. A method of extended multiplicative signal correction (EMSC) is put forward to decrease the influence of scattering on measurement results. The method is validated and the results show that the measurement accuracy is improved. Based on the above mentioned, the current optical methods are analyzed comprehensively from the mechanism. And the following conclusion is drawn that the lack of the physical base and ambiguity of optical mechanism are the essential reasons which prevent the near-infrared optical measurement technique from making breakthrough in application of measurement of milk composition.Optical model based on the interaction between light and milk is established. According to the condition of the practical application, a fiber measurement system is produced. A second order scattering radioactive transport model is developed to describe the transport of light in milk. Based on the model, the effects of the changes of milk characters on the transport of light are discussed, the relation between the optical signal and milk characters is presented. The results show that the changes of size distribution are the major factors and the volume fraction and index of refraction is minor factors for the transport of light in milk. The model is validated by an experiment.Two key factors, temperature and homogenization, influencing the practical application of the optical measurement techniques on milk composition measurement are studied comprehensively. The effect of temperature on the optical measurement of milk composition is studied, and the mechanism of effect is illustrated. A method of a global temperature correction model is presented to compensate the effect of temperature and the method is validated by experiments. The effect of homogenization on the microcosmic state of milk is analyzed. The unhomogenized milk samples are measured and the measurement accuracy is evaluated. The following fact is found that the low measurement accuracy relates to the changes of the status of unhomogenized milk with the milk component contents. According to this, a method of piecewise submodels based on the component contents is presented. The results show that the application of the method improves the measurement accuracy.