title: Improved microbiological assay for penicillin residues in milk and dairy products.
abstract: The microbiological assay for penicillin residues in milk was improved. Acidification of milk with phosphoric acid to pH 4.5, centrifugation to remove precipitated proteinaceous matter, adjustment of pH to 6.0, a second centrifugation, and the use of a 2% agar base layer resulted in the consistent measurement of 0.01 unit penicillin activity/ml milk. Sarcina lutea was used as the assay organism. Recoveries in milk averaged 94%, in nonfat dry milk 84%, in cottage cheese 97%, and in cream cheese 94%.
mesh_terms: D000818:Animals; D001681:Biological Assay; D002417:Cattle; D002611:Cheese / Q000032:analysis*; D008892:Milk / Q000032:analysis*; D010406:Penicillins / Q000032:analysis*; D012505:Sarcina / Q000254:growth & development
chemical_list: D010406:Penicillins