The Study Of The Chemical Composition In Milk And Dairy Products

Chemical compound of milk and dairy products have been studied. Gas chromatography-mass sepectrogram (GC-MS) was used for the determination of fatty acids, saturation fatty acids were the major contituents, the quantify was from 50 % to 70 %; oleic acid was the major contituent of unsaturation fatty acids and the quantify was from 20 % to 35 %; The samples'disposal method of ultraviolet spectrophotometry method (UV) was developed for the determination of protein. There was not notable difference between the UV method and Kjedahl france's method(P>0.05); The recovery rate was 99.08 %～104.9 %. The optium conditions of pre-column derivatization-HPLC were explored for the determination of penicillin residues in cows'milk, the minimum detective limit was 10.46μg/kg. And the method is adapt to the analysis of penicillin residues in cow's milk.GC-MS was used for the determination of fatty acids in milk and dairy products: Rose-Gettlieb method was applied in extraction of fatty oil from samples, potassium hydroxide-methanol solution methylation. 29 samples were analyzed by gas chromatography-mass sepectrogram, the results indicated that the major fatty acids'carbon chains were from 8 to 24, each fatty acid has different conent in different samples and the content was determined by area normalization.UV method was improved for the determination of protein in milk and dairy products: Rose-Gettlieb method was applied in extraction of fatty oil from samples, the handle shaking 2 min was superseded by ultrasonic 30 s. The optimum temperature of protein hydrolysis was 22-25℃. Detection wavelength was 280 nm. Area-external standard method, the liner range of determination for solid dairy products was 0.1415 mg/mL to 0.5660 mg/mL, and 0.1684 mg/mL to 0.6060 mg/mL for liquid milk, relation coefficient r=0.9999; the coefficient of variation was less than 0.2862 %. The method is environmental, simple, fast, accurate and feasible. Pre-column derivatization-HPLC was improved for the determination of penicillin residues in cow's milk: The orthogonal test was applied for determination the optimum conditions of the reaction that penicillin reacted with mercury chloride catalyzed by 1, 2, 4-trizdazole. The optimum conditions were 1.5 mL derivatization solution, 65℃water bath heating 5 min when the penicillin(0.5120 mg/mL) was 1 mL. Kromasil C18 chromatogram column, diode array detection, ethionine-phosphate buffer solution (0.1 mol/L include 0.015 mol/L sodium thiosulfate) = (30∶70,V/V) as mobile phase, and the flow-rate was 1 mL/min; Colum temperature was 25℃; Detection wavelength was 324 nm; Area-external standard method, the liner range of determination was 0.2520μg/mL to 1.512μg/mL, relation coefficient r=0.9999; The coefficient of variation was less than 1.941 %;The recovery rate was 95.24 %～109.5 %.