Heat-sensitive Inhibitor(s) Produced in Poor Quality Raw Milk1

Abstract

As bacterial numbers in raw milk increased to millions and pH decreased to 6.3 and lower, inhibitory substances were produced that gave positive tests by the Bacillus subtilis disc assay and Sarcina lutea cylinder plate method. These substances were inactivated by heat treatment. The inhibitor was not lactic acid. Results of our study emphasized that all laboratories that test raw milks for antibiotics must be certain to heat samples before reporting a positive test result for inhibitor. If a heat-sensitive inhibitor is found in raw milk, one should evaluate the quality control program.