HEAT RESISTANT BACTERIA IN RAW MILK

Abstract

Summary(1) The methylene blue test at 37°C. was found to be a poor indicator of unsatisfactory sterilisation of farm dairy equipment, though there was a broad, general relationship between methylene blue reduction time at 37oC. and the magnitude of the thermoduric colony count at 30°C.(2) Approximately two‐thirds of the samples which failed on the statutory methylene blue test had thermoduric counts under 10,000 suggesting that the former is more likely to indicate inadequate cooling of the milk than unsatisfactory methods of production.(3) A combination of the laboratory pasteurisation test and a direct keeping quality test at 19°‐20°C. by clot on boiling is considered more useful for advisory work on dairy farms than a combination of the laboratory pasteurisation test and methylene blue reduction, in that the former pair give a better indication of both unhygienic methods of milk production and of the keeping quality of the milk.(4) For advisory work at country creameries, it is suggested that the laboratory pasteurisation test could be usefully applied to milk supplies reducing methylene blue at 37oC. within 1 hour in summer and 2 ½hours in winter.