Quaternary ammonium compounds in milk: detection by reverse-phase high performance liquid chromatography and their effect on starter growth.

A reverse-phase HPLC method is described that permits detection of quaternary ammonium sanitizers in milk. The commercial mixture of quaternary ammonium sanitizer used, n-alkyl (50% C14, 40% C12, and 10% C16) dimethyl benzyl ammonium chloride, was extracted from raw and homogenized milks by the Mojonnier milk fat extraction protocol, selectively eluted from the reverse-phase column in the presence of organic solvent and ion-pairing agent, and then analyzed by diode array detection at 217 and 280 nm. Quaternary ammonium sanitizer concentrations in augmented milk samples in the range of 1.0 to 60 micrograms/ml were analyzed with high precision as indicated by a small variance around the mean. Starter culture strains currently in use for manufacture of various fermented milk products available in the Department of Microbiology Culture Collection were examined for their sensitivity to quaternary ammonium sanitizer. All strains were greatly inhibited by as little as 20 micrograms/ml in milk; some were inhibited by only 10 micrograms/ml.