Research Of The Determinative Methods Of Two Antibiotic Residues In Cows' Milk

Antibiotic residues in dairy products have been an important factor which restricts the development of dairy farming. We developed this investigation in order to determine antibiotic residues in cows' milk quickly and briefly, by which we can supply theoretic foundation and technical instruction for determination of antibiotic residues in dairy enterprise and food supervisal department.Chapter one: Determination of antibiotic residues in cows' milk by microbiological methodWe choose Streptococcus thermophilus as test bacteria in this study. When the indicator (TTC) is added into milk samples, which have been co-cultivated with test bacteria, the samples' color would change. According to this change, we can determine the antibiotic residues in cows' milk. Red stands for negative, however no color change is a sign of positive sample. We analyze milk samples obtaining from 5 cows by this method, then the elimination of antibiotic residues is obvious. This method is simple, easy to operate and not requiring expensive apparatus or equipments. While time-consuming, unquantitatible are it's shortage. The results of this method only represent the antibiotics' gross, so we can't know antibiotics' kind and the quantities of each respectively.Chapter two: Determination of antibiotic residues in cows' milk by HPLCHPLC was in common use in determination of antibiotic residues of animal origin foods , especially predominant in multi-residues analysis.I . HPLC determining TC and PG simultaneously by duel wave length detector.We developed a detective method finally in this experiment. By which we can determine two different kinds of antibiotics: TC and PG, in just a single analysis by duel wave length detector. Their retention value are as follows: PG, 6.356min; TC, 8.580min, however the detective sensitivity was different for TC and PGThe concentration of TC and the peak aera have good linear relation at the range from 0.08μg/mL to 2.0μg/mL. Relation coefficient: R2=0.9999; precision: 3.42%-4.44%; recovery: 65.4%-80.5%; minimum detective limit: 35ug/kg; minimum quantitive limit: 58μg/kg. This method is suit for the analysis of TC residues in milk. We analyze milk samples used this method, and the elimination of TC in milk is obvious.However as for PG, the detective sensitivity is low and the minimum detective limit is about 400μg/kg, which is far away from the maximum residue limit 4μg/kg set by governments. So we could not detect PG residue in milk samples, even if on the first day.II. HPLC determining PG by single wave length detector and derivated before analytical column.We founded this method for determining PG by sigle wave length detector and derivated before analytical column. During which PG react with mercury chloride catalyzed by 1,2,4-triadazole, the product of this reaction have maximum absorption at 325nm.The concentration of PG (corresponding to the derivate) and the peak aera have good linear relation at the range from 0.3μg/mL to 4.0μg/mL. Relation coefficient: R2=0.9999; precision: 4.1%; recovery: 78.4%-98.1%; minimum detective limit: 2.8μg/kg; minimum quantitive limit: 29.0μg/kg. This method is suit for the analysis of PG residues in milk. We used this method to analyze milk samples, and the results showed that the elimination ofPG in milk is obvious.Chapter three: Determination of antibiotic residues in cows' milk bychemical methodThe mechanism of this method is that PG can react with Benedict reagent under the condition of boiling, and the product of this reaction is CU₂O, which is brick red precipitate. Adding 3 drops Benedict Reagent to 1mL milk, boiling for 5 min, now we can determine PG residue in milk according to the change of samples' color. We did this experiment for several times, finally we concluded that the crude milk was not fit for this experiment. Then, We remove milk lipid by centrifugation at 4 degree, deprotein and extract whey by acetone, by using the reaction between reductive saccharide and phenyl hydrazine, as well as certain enzymes related to the break-down of lactose. But...