Validation of Steins/Arla Foods method for lactate fermenting clostridia in milk

Sammanfattning: One of the most serious and economically important defects caused by clostridia in milk products is the late blowing of semi-hard cheeses. Clostridia occur naturally in soil and can contaminate milk through crops contaminated by dung and soil followed by a less successful silage process, that give them opportunity to grow unaerobically. When anaerobic conditions occur, such as storage of semi-hard cheese, they ferment lactic acid to butyric acid and the gases CO2 and H2. At the fusion of Arla and MD Foods, a series of changes were conducted on the MPN method for lactic acid fermentation for clostridia in milk. These changes resulted in an increased accuracy due to an increased number of test tubes and the change of media from MRCM to BBB, Bryant & Burkey Broth, that was thought to be more selective for Cl. tyrobutyricum, the organism mostly found in hard cheese. When the number of dairy farmers that were given quality reduction fines increased, the new method was suspected and a validation was conducted. The validation included inoculation of different clostridia and bacillus strains into BBB substrate and enzymatic testing of positive samples with Rapid ID 32A. The inoculation result showed that almost all tested different clostridia strains could grow in BBB substrate. Test on BBB positive tubes with Rapid ID 32A resulted in 95% clostridia of which 70% was Cl. tyrobutyricum. These results correlated well with earlier studies on MRCM substrate and the increase in quality reduction fines probably depended on the larger number of test tubes used in the new method rather than the change of substrate.