Liquid Chromatography Verification of Tetracycline Residues in Milk and Influence of Milk Fat Lipolysis on the Detection of Antibiotic Residues by Microbial Assays and the Charm II Test

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Abstract
Farm milk samples, which were positive in the routine assay for inhibitory substances detected by the Arla microtest but negative in the Delvotest SP, were used in the study. All samples analyzed gave positive results in the determination of tetracyclines and macrolides by the Charm II microbial receptor tests. To confirm the presence of tetracyclines, liquid chromatography and the Charm II immuno-receptor test were used. All samples, except one, showed negative results in the analyses by both these methods. This suggested that some other factor(s) was causing the observed positive results for tetracyclines and macrolides. Circumstantial evidence indicated that free fatty acids (FFA) may be a causative factor. Consequently, the influence of FFA on the Arla microtest, Valio T101, Delvotest SP, and the tetracycline and macrolide determinations by the Charm II test was investigated. Lipolysis of milk fat was induced by the addition of human blood serum, followed by storage for 24 and 48 h at 4°C. Samples wer...

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