Treatment of lactating cows with antimicrobial agents can result in the presence of drug residues in milk. Tests available for the screening of antimicrobial residues have been developed, and often validated, on raw milk and are not immediately applicable to dairy products such as whole milk powder, skimmed milk powder, whey, condensed milk, buttermilk, etc. Many dairy products require special preparation before they can be used in screening procedures routinely used for raw milk.
This article presents ways of preparing various dairy products to obtain appropriate test samples. Detailed procedures are given for the reconstitution of dried samples such as milk powder and for the preparation of samples of cream, butter, yoghurt and cheese. Particular attention is paid to the dilution necessary for test samples of various types.
Keywords: Antimicrobial, Contaminant, Dairy, Food safety, Milk, Drug residues, Sample preparation, Screening, Veterinary medicines