Heat stable inhibitors produced in raw milk

Twenty raw farm milk samples were tested for inhibitory substances before and after being kept at room temperature until the pH fell to less than 6.3 but greater than 6.2. The tests were done using the IDF-method and the commercial Thermocult method. In both methods B. stearothermophilus var. chalidolactis is used as the test organism. In two instances a thermostable inhibitor was produced with an inhibitory potential greater than 0.01 IU/ml penicillin standard. The IDF-method was found unsuitable for the study of relatively small concentrations of antibiotics or other chemotherapeutics in milk.