Improved microbiological assay for penicillin residues in milk and dairy products
Katz, S.E.; Fassbender, C.A.
Journal - Association of Official Analytical Chemists 61(4): 918-922
1978
ISSN/ISBN: 0004-5756 PMID: 681264 Document Number: 130999
The microbiological assay for penicillin residues in milk was improved. Acidification of milk with phosphoric acid to pH 4.5, centrifugation to remove proteins, adjustment of pH to 6.0, a 2nd centrifugation, and the use of a 2% agar base layer resulted in the consistent measurement of 0.01 units penicillin activity/ml milk. Sarcina lutea was the assay organism. Av. recoveries of added penicillin were 94% from milk (0.01-0.1 units added/ml), 84% from dried skim milk (1-10 units added/10 g), and 97 and 94% resp. from Cottage and cream cheeses (0.01-0.1 units added/10 g cheese).