Optimization of a Multi-Residue Screening Method for the Detection of 71 Antimicrobial Residues in Milk Products: the Case of Labneh

Labneh is a dairy product highly consumed in Lebanon, prepared from straining yogurt. Because there is a lack of surveillance of the antimicrobial residues (AMRs) in milk and dairy products in Lebanon, this project was launched to develop a screening method for the detection of AMRs in labneh. In this study, we optimized a multi-residue screening method to detect 71 AMRs based on liquid-liquid extraction using buffered acetonitrile with 2 M ammonium acetate followed by freezing out the supernatant for 30 min at -23 & DEG;C. The extracts were then analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). This method was then validated against the Guidance (EU) CRLs 2010/01. The performance of the method showed a good specificity with no false negative rate and detection capabilities (CC & beta;) were below maximum residue levels (MRLs) for all analytes. In addition, this method demonstrated acceptable recoveries estimated in the range 70-130% for 92% of the analytes and the precision was below 30% except for a few macrolides and some & beta;-lactams with an intra-lab reproducibility ranging between 7.30-40.61% and 2.90-47.85%, respectively. Our results showed that the developed method can be applied as a screening method and with acceptable variation in quantitation for the majority of AMRs.