[Incidence of foreign substances in raw and pasteurized milk]

In 1980 to 1982, the occurrence of inhibiting substances, herbicides and chemical elements contaminating raw farm and bulk milk and pasteurized milk in different stages of technological processing was studied in the input regions of 19 dairies of the Lacrum Brno concern corporation. Residues of inhibiting substances were demonstrated by the thin-layer microbiological diffusion disk method using the testing strain of B. stearothermophilus var. calidolactis, to be present in raw milk (9.1% out of 143 samples) as well as in pasteurized milk (2.0% out of 151 samples). Chromatographic method (sensitivity 0.01-0.05 mg.kg-1 milk) was used for examining 135 raw milk samples for the occurrence of herbicides based on diazines and triazines. Herbicides were demonstrated to get into milk; residues were found in 45 samples (33.3%). Atomic absorption spectrophotometry was used for examining 143 raw milk samples for the contents of zinc, copper, iron and manganese. As to zinc content, 100% of the samples met the standard, as to iron content 99%, and as to the content of copper, 89% (Ministry of Health Directives, No. 50, 1978). The content of manganese remained within the range up to 0.1 mg.kg-1 milk in 60% of the samples. Out of the 135 milk samples (101 raw, 34 pasteurized milk ones) examined for the content of lead, four samples (3%) failed to meet the limit of the highest admissible level.