Effect Of Homogenization On Near-Infrared Diffuse Reflectance Spectra Of Milk And Its Mechanism Research

The nutrition of fresh milk is comprehensive and rich.Accurate detection on main components of milk is directly related to the evaluation of milk quality and the rights and interests of consumers.At present,the detection of milk composition based on near-infrared spectroscopy has made rapid development.However,the light scattering of fat globules with larger particle size in raw milk is very unstable,which is not conducive to the accurate detection of milk composition by optical method.At the same time,the size distribution of cow's milk has a great influence on optical measurement,while the homogenization treatment can improve the size distribution of cow's milk.Therefore,it is of great significance to explore the influence of the homogenization treatment on the near-infrared spectra of cow's milk.In order to get the milk samples with different particle size distribution and to analyze the effect of homogenization treatment on milk optical properties,fresh milk was used as the research object in this paper.Based on the high pressure homogenization treatment,the effects of different homogenization parameters on milk homogenization were analyzed by laser particle size analyzer and biological microscope.The influence of homogenization treatment on absorption coefficient and scattering coefficient of milk samples in the band range of 950~1650nm was analyzed based on single integrating sphere technique.And models based on near-infrared diffuse reflectance spectroscopy were established to predict the main components content of fresh and homogenized milk.The main work and results of this paper are as follows:(1)Homogenization times,homogenization pressure and inlet temperature are the three main factors affecting the homogenization effect of milk.With the increase of homogeneous pressure,two-stage homogenized milk has better effect than primary homogenized milk at inlet temperature of 25±2?.The two-stage homogeneous treatment was used in the further study and the second-stage homogeneous pressure was set to 5MPa.(2)Under different inlet temperatures(25±2?,35±2?,50±2?),with the increase of homogeneous pressure,the fat globules of homogenized milk gradually became smaller and was distributed more evenly.With the increase of inlet temperatures at certain homogeneous pressure(30/5MPa,40/5MPa,50/5MPa),the milk size distribution was also constantly improved.When the homogeneous pressure and inlet temperature were50/5MPa and 50±2?,respectively,the size distribution of milk fat globules stayed in arelatively stable state by observing the milk microscopic structure.The secondary homogeneous treatment,homogeneous pressure of 50/5MPa and inlet temperature of50±2? were chosen as the final optimal parameters of milk homogenization treatment.(3)In the range of 833~2500nm,the curve trends of near-infrared diffuse reflectance spectra of raw milk and milk homogenization were consistent,but the absorbance values of homogenized milk were all less than raw milk.In the multiple measurements of one sample,the spectral curves of raw milk had more obvious fluctuation than that of homogenized milk,which indicated that the homogenization treatment could improve the measurement stability of milk spectra.(4)In the range of 950~1650nm,the trends of reflectivity and transmissivity curves of raw milk and homogenized milk were consistent.But homogenization treatment had great influence on the values of reflectivity and transmissivity.Under certain wavelength,the reflectivity of homogenized milk was greater than that of fresh milk,but the transmissibility of fresh milk was greater than that of homogenized milk.Meanwhile,the effect of homogenization treatment on milk absorption coefficient was smaller than that on scattering coefficient.The absorption coefficient of homogenized milk was smaller than that of fresh milk,but the scattering coefficient of homogenized milk was higher than that of fresh milk.Under the pressure of 20/5~50/5MPa,the absorption coefficient and the scattering coefficient of homogenized milk both reached a relatively stable state.(5)Samples of raw milk and homogenized milk were divided into calibration set and prediction set in proportion of 3:1 based on SPXY method.Prediction models were established on milk fat,protein and water content based on four modeling methods,respectively.The results showed that both homogenized milk and fresh milk,PLS models established on characteristic variables extracted by PLS-UVE method had the lowest RMSEP and highest RPD.Under the optimal modeling methods,the RMSEP of fat,protein and water content of homogenized milk were 0.123%,0.078% and 0.160%,respectively;The RMSEP of fresh milk fat,protein and water content were 0.208%,0.107% and 0.338%,respectively.Homogenization treatment significantly improved the prediction accuracy of milk fat and water content,and also improved the prediction accuracy of milk protein content,which provided the theoretical basis and practical support for the further development of the accurate prediction of cow milk composition by spectral technology.