Agroscope, 3003, Bern, Schweiz

Comparison of methods for quantifying butyric acid bacteria in milk

As part of a milk processor’s annual winter campaign for monitoring the contamination of raw milk with anaerobic spores harmful to cheese – also called butyric acid spores – the analysis methods currently used in Switzerland (MPN method according to CNERNA and filtration method according to Bourgeois) are compared with a new method (SY-LAB). To this end, 93 milk samples from silage-free and 217 samples from non-silage-free milk production were examined with all three methods. In the latter group, the new method delivered more impressive results than the other methods, thanks to its greater precision and a very large measurement range of 44 to 19,000 spores/L. In the milk samples from silage-free milk production, the new method detected spores in only 9 % of the samples, the filtration method in 29 % (detection level of 25 spores/L) and the MPN method in 44 % of the samples (detection level of 53 spores/L). In combining the filtration method’s advantage of specificity with the robustness of MPN methods, the new method could offer advantages not just for silo milk, but also for silo-free milk, despite its lower sensitivity.

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