Physichemical Properities Of Goat And Cow Milk And Adulteration Detection Of Cow Milk In Goat Milk

The key point of the quality and safety of dairy products is to control rawmilk. Therefore, this work made a comparative study of goat and bovine milkprotein content, composition, alcohol stability and curd characteristics. An directcompetitive ELISA was also established based on bovine α-LA and α-CN, whichcan detect the adulteration of bovine milk in goat milk rapidly, sensitively andaccurately.We made a comparative study on the physical and chemical characteristicsof goat and bovine milk. Skim milk samples were tested by Kjeldahl andSDS-PAGE to determine protein content and composition. From the result wecan see that the goat’s and cow’s milk protein concentration were （3.43±0.06）g/100mL and （3.19±0.07）g/100mL respectively（in the confidence level of95%）and there were some differences between the protein composition of thetwo. From the PAGE electrophoresis pattern we can see that α-CN was the mostin bovine milk casein but β-CN was the most in goat milk casein. The alcoholstability were46±1,42±2,40±1and78±1,78±1,78±1（%V/V）,the coagulationtime were297±2,310±2,266±2and571±3,590±1,485±1（S）for raw,pasteurized and thawing-frozen milk samples. All above just showed that thecolloid stability of goat milk was worse than bovine milk.The New Zealand white rabbits were immunized by bovine α-LA and α-CNand collected when the rabbit serum’s titer was euough high. The rabbitanti-bovine α-LA-IgG and α-CN-IgG samples were purified by differentgradients of saturated ammonium sulfate and protein A affinity chromatograph,whose titer can be reached1:16000, protein concentration were0.35mg/mL,0.43mg/mL, and the purity88.31%,89.23%, respectively. The relative affinity of anti-α-LA-IgG and anti-α-CN-IgG were determined by Ammonium thiocyanateelution method, the affinity index with α-LA were2.6mol/L and1.1mol/L; theaffinity index with α-CN was1.6mol/L and2.5mol/L. The specificity ofanti-α-LA-IgG was good, while there was a certain cross reactions betweenanti-α-CN-IgG and κ-and β-CN. Both antibodies had a bit of cross reactions withgoat milk. After dealing with antibody modification technologies, thesecross-reactions were significantly reduced.α-LA and α-CN of bovine milk were labeled with horseradish peroxidase bythe method of sodium iodide oxidation. From the results we can see that whenthe number of the molecules of HRP and α-LA ratio was1.5:1, we can get thebest result that the conjugative rate was25.4%, and the enzyme labeling rate was85.7%; and for α-CN, when the ratio was also1.5:1, we can get the best resultthat the conjugative rate was43.8%, and the enzyme labeling rate was84.49%.The titer of the two labled antigens were1:320and1:640resppectively.The best coat concentration of the antibodies （anti-α-LA-IgG,1:160; andanti-α-CN-IgG,1:320） and the best labled antigens dilution （1:20） weredetermined by Checkerboard titration. The plates were blocked by200μL1%Gelatin, with1h. Skim milk dilution was1:80. Then the direct competitiveELISA for adulteration detection of bovine milk in goat milk were developedbased on anti-α-LA-IgG and anti-α-CN-IgG, respectively. The linear range of themethods were both0%to50%（V/V）, the lowest detection limits were2.5%and4%and the coefficient of variation were less than5%.By comparing the physichemical properties and the colloidal stability ofgoat milk and bovine milk, this work can supply a theoretical basis for thescientific and reasonable use of goat milk and the production of goat dairyproducts with unique features; The direct competive ELISA we developed in thiswork were based on bovine α-LA and α-CN, becauseof their high specificity,reproducibility and sensitivity, the two methods can be used as the techniques fordetection of bovine milk in goat milk and its products.