ENUMERATION OF PROPIONIBACTERIA IN RAW-MILK USING A NEW SELECTIVE MEDIUM

Propionibacteria were enumerated using a new medium in 202 raw milk sa mples taken from tanker lorries, collected over a I-year period from 9 regions of France. This medium, called Pal Propiobac, has been compar ed with yeast extract lactate agar (YELA) for its efficiency to enumer ate propionibacteria in 29 of these milk samples. Propionibacteria cou nts were of the same order of magnitude on both media. However, total counts on YELA (reflecting all the milk flora able to grow on the medi um) were markedly higher than total counts on Pal Propiobac, which sho ws a higher selectivity of the latter medium towards milk microorganis ms other than propionibacteria. Moreover, more than one-quarter (8 of 29) of the milk samples could not have been enumerated on YELA because of the lack of colonies of typical appearance on this medium. Propion ibacteria counts in raw milk ranged between less than 10 cfu/ml to 1.3 10(4) cfu/ml. The variations observed for milk samples collected the same day in a given region were of the same order of magnitude as vari ation depending on regional or seasonal factors. The geometric mean of propionibacteria counts of all the tested samples was 2.19 log cfu/ml , with a standard deviation of 0.58. The significance of the propionib acteria content of milk for cheese technology is discussed.