Study On Assessment Of Milk And Dairy Products Quality

The quality of dairy products has been a prominent problem with the development of dairy industry. Rapid, objective and effective evaluation and control the quality and freshness (shelf life) of milk and dairy products is the urgent needs for a modern dairy industry and the relevant regulatory authorities, and it has also been one of the research hot spots in the dairy industry.In this paper, different forms of adulterated milk samples and milk products from different companies produced by different heat treatments were chosen as the research objects. Preliminary exploration has been done for the application of multi-frequency pulse electronic tongue in rapid testing and evaluating milk and dairy products quality. And the low-field nuclear magnetic resonance was used for studying the relaxation phenomena and laws of fat and water in dairy products, in order to provide some experimental basis for its application in quality evaluation for dairy products. The main research work is as follows:(1) Rapid detection of adulterated milk based on electronic tongueDifferent forms of adulterated milk samples were analyzed by the electronic tongue, which was developed by author's research group. Milk samples adulterated with water, sodium chloride, sucrose, urea or bean oil, reconstituted milk and UHT sterilized milk samples were analyzed. The corresponding methods and procedures of the dairy products quality evaluation and control were established. The sensor arrav and correlated test parameters were analyzed comparatively with the different electrodes and the adaptive electrodes were manufactured by aurum, palladium, tungsten, titanium, argentine and platinum. The experiment showed that electronic tongue could discriminate not only between UHT sterilized milk and different kinds of adulterated milk, but also UHT sterilized milk, pasteurized milk, reconstituted milk and their mixed milk. The application of electronic tongue in adulterated milk with different additive proportions showed the similar result, too. The Soft Independent Modeling of Class Analogy/Statistical Isolinear Multi-Category Analogy (SIMCA) discrimination model of milk, based on Principal Component Analysis (PCA), was set up. Six kinds of adulterated milk samples were prepared to validate the model, while 5 replicates of each sample were prepared. The discrimination accuracies of five kinds of adulterated milk by SIMCA model were 100%. The prediction models of adulterants in quantitative analysis based on Partial Least Squares (PLS) were established. In the single-factor test, the prediction model for each adulterated substance:salt, sugar or urea was good and the correlation coefficients were all above 0.980.(2) Assessment of quality and freshness based on the electronic tongue for milk products of different brands and heat treatment processesFive brands of UHT sterilized milk and two brands of pasteurized milk were analyzed for the evaluation of quality properties and freshness by the electronic tongue. Principal Component Analysis(PCA) was used for data processing, the experiment showed that electronic tongue could discriminate not only between UHT sterilized milk and pasteurized milk, but also different brands of UHT sterilized milk or pasteurized milk. The application of electronic tongue in pasteurized milk products at 20℃or 4℃showed the similar result, too. The electronic tongue as a kind of modern intelligent sensory instrument shows a greater potential in the evaluation of quality and freshness for dairy products.(3) The relaxation of dairy products in low-field nuclear magnetic resonance (LF-NMR) testTransverse relaxation time distribution of milk can be divided into: T21(0.1-10ms, Bound water), T22(10-100ms, Milk fat), T23(100-1000ms, Free water).Milk samples with different butter content was prepared for LF-NMR experiment, the results showed that T22 area percentage could accurately reflect the changes of milk fat content in the samples. Different amount of stabilizer were added into skim milk, the test results showed that, the sample stability and the appropriate added amount of stabilizer could be evaluated according to T2 relaxation time.(4) Evaluation of the quality and freshness of milk during storage in refrigeratorIt was found that, there is a clear correlation between the relative T22 area and fat content of the samples, a definite increasing trend was showed for T23 with the storage time, indicating that LF-NMR technology can be used in research fat content and the mobility of free water in the samples, and the impact on the quality and stability of the samples. The results of electronic tongue analysis showed that there were significant correlations between the principal component scores with the total number of colonies, protein content, titratable acidity and T23, etc.