Studies On Detective Methods For Reconstituted Milk In Liquid Milk

Milk is an almost nearly complete natural food, which is also widely used as an ingredient in many formulated foods. Adulteration of fresh milk by adding reconstituted milk or the selling of reconstituted milk as the fresh product can be economically advantageous when either a surplus of milk powder exists or in countries where the importation of dried milk powder is subsidized. Adulteration malpractice creates unfair competition, could lead to market distortions, which in turn may impact the local or even the international economy. When legislation prohibits such practice, the detection of reconstituted milk depicted as fresh milk or mixed with fresh milk, becomes an analytical problem. Methods of detection have depended on changes brought about by heat treatment and drying of milk powder in the molecular structure of milk constituted, However, the methods above require tedious pretreatment procedures, are time consuming and expensive. The purpose of this study was to develop a rapid, simple and precise method to detect the presence of reconstituted milk.In this dissertation, the differences between raw milk and reconstituted milk on protein physical and chemical properties were first studied. Then some indexes were detected by ultraviolet-spectrophotometer, high performance liquid chromatography, radioimmunoassay, semiautomatic biochemistry analyzer, fluorometry, color difference meter and Malvern Zetasizer 4 instrument. The sample treatment method and test condition were further researched. At last, these indexes of a large number of raw milk and reconstituted milk samples were determined and analyzed in order to study the limitation of detection for reconstituted milk adulteration. The main results are as follows:1 .The differences between raw milk and reconstituted milk were detected by ultraviolet-spectrophotometer, high performance liquid chromatography, radioimmunoassay, semiautomatic biochemistry analyzer, fluorometry, color difference meter, malvern zetasizer 4 instrument. It showed that the whey, α-lactalbumin and β-lactoglobulin concentration of raw milk were significantly higher than that of reconstituted milk (P<0.01), the biological activity factors of raw milk were significantly higher than that of reconstituted milk (P<0.01), thesebiological activity factors mainly include insulin growth factor, epidermal growth factor and immunoglobulin G. There was significantly difference between raw milk and reconstituted milk on available lysine content (P<0.05). There were also significantly difference between raw milk and reconstituted milk in the L value and b value (P<0.0\). The research indicates that there is significantly difference between raw milk and reconstituted milk in the index mentioned above.2. The Seliwanoff s method was proved to be the best method by comparing three lactulose spectrophotometry methods. The Seliwanoffs method was feasible by using the Folin-phenol method as comparison. It couldn't detected effectively lactulose in milk sample, but the raw milk and reconstituted milk could be difference by the Seliwanoffs method, The Seliwanoffs method could be used to detect the presence of 20% reconstituted milk in raw milk and 40% of reconstituted milk in pasteurized and UHT milk, respectively.3. The a-lactalbumin, J3-1actoglobulin and immunoglobulin G differences between raw milk and reconstituted milk were detected by high performance liquid chromatography and semiautomatic biochemistry analyzer. Determination of immunoglobulin G could be used to determine the presence of 10% reconstituted milk in raw milk and pasteurized and raw milk, but it couldn't be use for UHT milk. Detection of a-lactalbumin could be used to determine the presence of 40% reconstituted milk in raw milk and pasteurized and raw milk, but it was only detect the presence of 60% reconstituted milk in UHT milk. It may be used to detect the presence of 20% reconstituted milk in raw milk and pasteurized by detecting |3-lactoglobulin, the limitation of detection reconstituted milk in UHT milk was 40%.4. The Tryptophan, advanced Maillard products fluorescence values were measured by fluorometry and the FAST index (fluorescence of advanced Maillard products and soluble tryptophan index) is calculated. Results showed that there were no significant difference (P> 0.05) between tryptophan, advanced Maillard products fluorescence values and FAST index of milk from different seasons, it appears that there exist significant difference (i><0.01) between raw milk and reconstituted milk. During storage, the advanced Maillard products fluorescence values and FAST index was increasing gradually, but tryptophan fluorescence values was dropping gradually, the storage temperature is higher the change tendency is more obvious. The tryptophan fluorescence values could be used to detect the presence of 10% reconstituted milk inraw milk and pasteurized and raw milk, but it was only detect the presence of 20% reconstituted milk in UHT milk. Calculation of FAST index could be used to detect the presence of 5% reconstituted milk in raw milk and pasteurized and raw milk, but it is only detect the presence of 10% reconstituted milk in UHT milk.