Study On The Content Of Essential Amino Acids And Its Changes In Milk

The law of the essential amino acids is changed in the dairy products in the process of production, processing and storage. It is researched in this thesis. The method of detecting the essential amino acids in dairy products was established by HPLC. The different essential amino acids levels were analyzed on milk from different varieties of cow and dairy raw materials. Changed laws of the stability of the essential amino acids in milk powder were also studied.The essential amino acids in dairy products can well be tested by using high-performance liquid chromatographic on Waters AccQ·Tag amino acid analysis column and the stationary phase with acetonitrile-water-Waters AccQ·Tag Eluent A solution as the mobile phase and 1.00 mL/min speed at gradient elution in the 37 "Cand UV detector in the 248 nm. The essential amino acids have a good separation. Acid hydrolysis method and alkali hydrolysis method were used in pre-processing.Pretreatment can decrease the interference and improve the sensitivity. The recovery was 95.2%-104.4%. The largest relative standard deviation was 8.20% and the variation coefficient was 2.54%.Vitamin and mineral elements which is included in the formula have a major impact of the essential amino acids in two to three times of the standard amount and showing significant reduction in the determination of the essential amino acids. The content of the essential amino acids is not significant impacted in adding the standard amount of nutrients.The change trend of thel essential amino acids and the change reasons in different Processing procedures were researched. Tryptophan and methionine in the Processing procedures were the most difficult to protect in all the essential amino acids, and their sensitivity were directly related to the sterilization temperature, oxygen and the dramatic extent of processing. The essential amino acids were affected by protein types and sources. The content of amino acids were influence by sterilization temperature, disinfection time and sterilization methods. The great impact of the largest amino acid in the processing technology of yogurt was that the histidine, threonine and phenylalanine had a substantial increase in the fermentation process. The changes were related with the fermentation bacteria. All kinds of essential amino acids were protected well in processing technology of pasteurized milk,it didn't cause any significant changes in nutrition. Phenylalanine demonstrated its outstanding features compared to other amino acids in the processing technology. The content of phenylalanine was relevant to the temperature and the degree how oxygen contact. The increase of phenylalanine may have a correlation with the transformation of tyrosine; the mechanism remains to be further studied.Different of the essential amino acids in the materials of milk powder on market and fresh milk from different varieties of cows were analysised. Huge differences among the amino acids in the fresh milk were studied varied with the cows; But the similar varieties cows, or from the same ancestors, or have a common origin cows had certain similarities in the essential amino acids. The essential amino acid in the whey and the whole milk powder from different country manifested definite differences, but the main differences were methionine and tryptophan. This was related to the processing of the raw materials and the source of the raw materials. In addition to specific brands, the differences among the essential amino acids in different infant formula brands which were sold on the market were getting smaller and smaller. The direction and the development of infant formula were the balance of amino acids and the amount adjustment of amino acids.Arrhenius equation was used to study the stability; chemical kinetics of the milk powder was also studied. Methionine and tryptophan in infant formula and whole milk powder were the most unstable essential amino acids. Their storage periods were about 2500 h-3000h. The activation energies varied from different amino acids, the greatest activation energy was the leucine 6.2438 E+6 J/mol in the whole milk and the smallest activation energy was the Met in the whole milk, for its activation energy were 4.4664 E+5 J/mol. It is known from the general information that the activation energy of the chemical reaction is between 42 kJ/mo-420kJ/mol. it can be drawn a conclusion from the number of the amino acid activation energy level in the milk powder that the essential amino acids degradation is not a simple zero-order reaction, or a reaction of amino acid degradation, is a complex process. The mechanism needs further investigation.