Milk analyzer is a high-end instrument specially for the dairy industry, mainly used in the quality control and product development of various dairy products (including high-viscosity yogurt). Main inspections: raw milk, fermented yogurt (the instrument itself is equipped with a high-viscosity pump), colorful milk beverages, UHT (ultra-high temperature sterilized milk), pasteurized milk, etc.
The milk analyzer can very accurately detect fat, protein, lactose, total solids, non-fat milk solids, free fatty acids, citric acid, density, sucrose, conductivity, acidity, total sugar, urea, casein, Freezing point and other components and detection of freezing point. It can be applied to the detection of raw milk, fermented milk, yogurt, colorful milk, various liquid milk, flavored milk and various milk beverages. It can be used for the research and development of dairy products, the control of semi-finished products in the production process (reducing the cost of raw materials), the quality control of finished products, and the quality of raw milk.
Milk test machine can detect fat in raw milk and various dairy products (some analyzers can detect animal fat and non-animal fat), protein, lactose, total solids, non-fat milk solids, free fatty acids, citric acid, density, sucrose, conductivity, acidity, total sugar, urea, casein, freezing point and other components. At the same time, the temperature of the sample can be controlled.
In the national standard, there are strict regulations on the indicators and testing of milk and other dairy products. The chemical analysis method is the national standard method. The determination of protein in chemical analysis methods often uses the semi-micro Kjeldahl method. The principle of the semi-micro Kjeldahl method is to heat the test sample with sulfuric acid and catalyst to decompose the protein. The decomposed ammonia combines with sulfuric acid to form ammonium sulfate. Then the ammonia is freed by alkalization distillation, and then absorbed by boric acid. Titrate with a standard hydrochloric acid solution and multiply the conversion factor according to the consumption of acid to obtain the protein content. This method requires that the difference between the two parallel determination results of the same sample should not exceed 1.5% of the average value; for lactose, high pressure liquid chromatography and the Rein-Enon method are used, and the difference between the two parallel determination results should not exceed 5% of the average value.
The chemical method is quite mature and can obtain high accuracy, but it takes a long time to get the result and cannot meet the needs of online measurement and analysis.
The mid-infrared spectroscopy analysis method is relatively mature, and almost impeccable analytical instruments have already come out. The Milk Scan series of rapid milk composition analyzers produced by the Danish FOSS company is one of them. The mid-infrared spectroscopy method uses the absorption of various components in milk to different wavelengths, and completes the determination of milk components by measuring the absorption coefficient and scattering coefficient. FOSS Milk 133 is an early product of FOSS, using interference filter technology, and its prediction accuracy CV value can reach the level of 5%. The FOSS Milk Scan FT120 milk analyzer, using Fourier technology, has a prediction value of 1% for fat, protein and lactose, and a prediction value of 0.8% for non-fat milk solids and total dry matter.
However, the mid-infrared spectrum analyzer is expensive, large in size, and complicated in operation and maintenance, and is not suitable for on-site operation and flow detection.
The protein content in milk can also be determined by ultraviolet spectroscopy. The principle of determination is that the aromatic ring residues of the protein and its degradation products in the milk can selectively absorb light of a certain wavelength in the ultraviolet region, and within a certain concentration range, light absorption has a linear relationship with the protein concentration, so by measuring the absorbance of the protein solution, the protein content can be measured.
Ultraviolet absorption spectroscopy has the advantages of fastness, simplicity, high sensitivity, and re-linearity. However, because non-protein substances may also cause light absorption in the ultraviolet part, and the interference of light scattering, there is low analysis accuracy.
Near-infrared spectroscopy analysis technology uses spectroscopy to analyze the composition and structure of substances. It has the advantages of fast, low cost, no damage to the chemical properties of the sample, and environmental protection. In recent years, it has been used in the field of analysis and testing, especially in the field of online analysis and industrial control. In the fields of agriculture, food industry, petroleum industry, pharmaceutical industry and clinical medicine, near-infrared spectroscopy technology has been successfully applied. The conventional analysis of near-infrared spectroscopy is similar to ultraviolet-visible spectroscopy, which is divided into transmission spectrum and diffuse reflectance spectrum.
In practice, different analysis techniques are used according to different sample properties. The absorption of different components of milk at different wavelengths is often used to establish multiple linear regression models. For example, fat has strong absorption peaks at 1212nm, 1392nm, 1729nm, 1763nm and 2144nm.
In the diffuse reflection test, protein has quite abundant absorption peaks at 1460nm～1570nm, 2050nm～2070nm and 2180nm. In China, some research institutes measured the diffuse reflectance spectrum of milk powder on the model 8620 milk powder analyzer of Pertone, and used 55 high-calcium milk powder samples to establish a model using multiple linear regression algorithms. The correlate coefficient of protein modeling is 0.96 and SEC is 0.196%.
At present, many foreign companies have developed milk powder analyzers based on near-infrared spectroscopy. However, due to the lack of representative models, the measurement accuracy of these products is not satisfactory. This is also a problem that the near-infrared spectroscopy needs to solve.
Ultrasonic detection technology uses the interaction between high-frequency waves and substances to obtain the physical and chemical properties of the measured substance. Ultrasound can be divided into longitudinal wave, transverse wave, surface wave and plate wave according to its wave type. In liquids such as milk, there can only be longitudinal waves, while the other three do not exist.
When ultrasonic waves pass through a medium, there are roughly three forms: compression waves, surface waves and shear waves. In the application, compared with the other two forms, the compression wave is the most important, which is the propagation form of the longitudinal wave. The transmission of compression waves in the medium is carried out through the compression and expansion of the medium; but the oscillation of this medium particle with the original position as the origin under the action of the sound wave still obeys Hooke's law, that is, the structure of the medium has no fundamental damage occurred during the transmission of sound waves.
Among the various components of milk, fat and other macromolecular substances have a greater impact on the attenuation of ultrasound, while protein and lactose have a greater impact on the speed of ultrasound. The components in milk can be divided into fat and non-fat milk solids. According to the contribution of the two major components to the ultrasonic attenuation and velocity, a model can be established to measure the percentage of each component, and based on the statistical relationship, the content of other components can be calculated. In this way, the percentages of various ingredients can be obtained. In recent years, great progress has been made in the field of ultrasonic milk composition measurement at home and abroad. The prediction accuracy can reach 5%, which can basically meet the requirements of online measurement and flow detection.
Ultrasonic measurement methods have many advantages over the optical methods mentioned above. The ultrasonic method has low requirements for the measurement environment, so the ultrasonic analyzer is very suitable for flow detection. Compared with optical devices, the ultrasonic probe has a lower price, which makes the cost of the ultrasonic milk composition analyzer lower, which is very suitable for small users. Coupled with the small amount of sample required for analysis, the instrument can be made small in volume and suitable for portable use.
Note: This article takes the ultrasonic milk detector as the main object of description.
The milk analyzer can easily detect the physical characteristics and composition of various dairy products. The detection methods are different and the results will be not consistent. The milk analyzer price of different models, brands and configurations varies greatly