| Fat,protein,lactose and total solids are important indicators in evaluating the nutritional and commercial values of milk.Therefore,monitoring the main compositions of milk has become an indispensable part in cow management.Chemical or physical methods are usually usedas traditional methods in detecting milk compositions,such as R?se-Gottlieb method for fat content,Kjeldahl method for protein content,high performance liquid chromatography method for lactose content and direct forced air oven drying method for total solids.These detection methods have high precision and good repeatability,but have some shortcomings such as low detection speed,complicated operation procedure and one parameter be detected at a time.To overcome these shortcomings,some technologies such as ultrasonic,dielectric properties and spectroscopy have been used to detect the main compositions of milk.Among them,spectroscopy technologies have attracted more attention because of the high detection speed and the ability of measuring multiple milk compositions simultaneously.However,few studys about the effects of milk composition on the optical properties,such as reduced scattering coefficient(?_s')and absorption coefficient(?_a),had been done.The mechanism of homogenization pretreatment to improve the prediction accuracy of milk composition based on spectroscopy was not clear.The price of milk compositions analyzers on the market were high,and it were unaffordable for small and medium-sized farms and dairy enterprises.To solve the above problems,this paper focused on the detection mechanism of milk main compositions and the development of portable milk analyzer based on spectroscopy.The main results were described as follows:(1)The effects and mechanism of fat,protein,lactose and total solids in milk on optical properties of milk in the wavelength range of 500-950 nm were studied based on integrating sphere technique and inverse adding doubling(IAD)algorithm.The results showed that the?_s'increased linearly with the increase of fat and total solid content in milk.After adding casein,the?_s'of milk increased,but the relationship between the variation of?_s'and the amount of casein was not clear.With the addition of lactose,the?_s'of milk had little change.The results explained why the reflectance spectrum acquisition method was better in predicting main compositions of milk and provided a theoretical basis for determining the spectral acquisition method of the milk analyzer.(2)Ultraviolet/visible(UV/Vis)spectra,visible/short-wavenear-infrared(Vis/SWNIR)spectra and diffuse reflectance multispectra of milk samples with different contents of fat,protein,lactose and total solids were collected,and the influence and mechanism of main compositions content of milk on the above three spectra were analyzed.The results showed that,in the wavelength range of 183-663 nm,the effects of milk compositions on the absorbance spectra were total solids,fat,protein and lactose in descending order.In the wavelength range of 633-1122 nm,the effects of milk compositions on the diffuse reflectance spectra were fat,total solids,protein and lactose in descending order.The results provided a theoretical basis for the accuracy difference in predicting the main compositions of milk by using spectroscopic techniques.(3)The influence and mechanism of homogenizing pressure on milk particle size distribution were analyzed.UV/Vis spectra,Vis/SWNIR spectra,NIR spectrra and diffuse reflectance multispectra of milk samples with different microstructures were collected.The results showed that with the increase of homogenization pressure,the particle size in the milk decreased obviously,and the particle size became closer to each other.In the wavelength range of 183-461 nm,the change of milk microstructure had a great influence on the spectra and the influence on the spectral stability depends on the wavelength.In the wavelength range of 633-1122 nm,the diffuse reflectance of homogenized milk were close to but slightly higher than that of fresh raw milk,and the spectral stability were higher.In the range of 901-1725 nm,the diffuse reflectance of homogenized milk were higher than that of fresh milk and the spectral stability were also higher.In the wavelength range of 410-940 nm,the diffuse reflectance multispectral of homogenized milk were higher than that of fresh raw milk,and the spectral stability was also higher than that of fresh raw milk.The results explained why high pressure homogenization could improve the accuracy of milk compositions detection based on spectral technologys.(4)A milk analyzer based on Vis/SWNIR diffuse reflectance spectroscopy was developed with a micro Vis/SWNIR spectrometer as the spectral detection module and a micro halogen tungsten lamp as the light source.Vis/SWNIR spectra acquisition software and milk compositions analysis software were also developed.Partial Least Square Regression(PLS)algorithm were used to establish the prediction models for the contents of fat,protein,lactose and total solids in milk.The performance of the developed milk analyzer was evaluated with independent samples.The results showed that,for fresh raw milk,the root mean square errors(RMSE)of fat,protein,lactose and total solids content were 0.14%,0.14%,0.08%and 0.27%,respectively.For homogized milk,RMSEs were 0.10%,0.12%,0.08%and 0.21%,respectively.The milk analyzer provides technical support for small and medium-sized farms or dairy enterprises to detect milk compositions quickly and in-situ.(5)A milk analyzer based on UV/Vis absortance spectroscopy was developed with a micro UV/Vis spectrometer as the spectral detection module and a deuterium lamp as the light source.UV/Vis spectrua acquisition software and milk compositions analysis software were also developed.PLS algorithm were used to establish the prediction models for the contents of fat,protein,lactose and total solids in milk.The results showed that,for fresh raw milk,the RMSE of fat,protein,lactose and total solids content were 0.35%,0.19%,0.13%and 0.46%.For homogized milk,RMSEs were 0.17%,0.14%,0.09%and 0.27%.The development of the milk analyzer shows that UV/Vis spectroscopy could also be used for multi-compositions,rapid and in-situ detection of milk,but the accuracy was lower than that of the milk analyzer based on VIS/NIR spectroscopy.(6)A milk analyzer based on diffuse reflectance multispectra was developed with 18-channels multispectral sensor as the multispectral acquisition module and a micro halogen tungsten lamp as the light source.Diffuse reflectance multispectra acquisition software and milk compositions analysis software were also developed.PLS algorithm were used to establish the prediction models for the contents of fat,protein,lactose and total solids in milk.The results showed that for fresh raw milk,the RMSE of fat,protein,lactose and total solids content were0.37%,0.34%,0.16%and 0.53%.For homogized milk,RMSEs were 0.23%,0.31%,0.14%and 0.41%.The development of the milk analyzer provides a solution for ultra-low cost,on-site milk compositions detection in small farms. |
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