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 qua ternary ammonium sanitizers in milk. The commercial mixture of quatern ary ammonium sanitizer used, n-alkyl (50% C-14, 40% C-12, and 10% C-16 ) dimethyl benzyl ammonium chloride, was extracted from raw and homoge nized milks by the Mojonnier milk fat extraction protocol, selectively eluted from the reverse-phase column in the presence of organic solve nt and ion-pairing agent, and then analyzed by diode array detection a t 217 and 280 nm. Quaternary ammonium sanitizer concentrations in augm ented milk samples in the range of 1.0 to 60 mug/ml were analyzed with high precision as indicated by a small variance around the mean. Star ter culture strains currently in use for manufacture of various fermen ted 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 mug/m l in milk; some were inhibited by only 10 mug/ml.