Study On The Determination Of β-Lactamase Residue In Milk

In this research, microbiological assay and Acid Meter were established for determination ofβ-Lactamase residues in milk,aiming to severe residues problem in milk to our country and having no perfect monitoring system,and some comparative studies had been done to obtained the optimal conditions of tow determination methods,.In order to provide theoretical basis and technical reference to different scale dairy enterprise and quality control department.The result indicated that Micrococcaceae were adapted to determineβ-lactamase residue in milk.The optimum accession quantity of lactobacillus was 1×10~9CFU/mL.the optimum temperature was 37℃, the optimum fermented time was 14~16hours.Antibiotic medium No.2 was used in the method of inhibition zone.The diameter of inhibition zone differences were showed between the positive groups and the negative control. The result shows that the optimal concentration was penicillin 0.100mg/mL, sulbactam 5μg/ml,β-lactamase 400U/ml,The detection limit of this method was found to be 4U/mL. Using the developed method, 18 (58.1%) of the 31 milk samples were positive forβ-lactamase.The principle thatβ-lactamase selectively decomposesβ-lactamase antibiotics like penicillin into acids leading to pH decline was considered to present a rapid and accurate method for the determination ofβ-lactamase residue in milk.β-lactamase at a constant final concentration of 100U/mL and penicillin were artificially added to antibiotic free milk and left to react for a certain period of time at an appropriate temperature. The optimal penicillin final concentration and reaction time and temperature were determined to be 10mg/mL, 60min and 33℃, respectively. The developed method exhibited a limit of detection of 8.92U/mL. Using the developed method, 5 (41.6%) of the 12 milk samples were positive forβ-lactamase.These two methods are both suitable for determination ofβ-lactamase in milk. microbiological assay is issensitive,accurate and reproducibility is good. Use of an acid meter is simple and rapid.