Lactobacilli in raw milk and in Cheddar cheese

Abstract

Summary: The lactobacillus flora of the mixed morning and evening milk of a single herd and of sixty Cheddar cheese made from this milk, unheated, was examined over a period of 12 months. Few lactobacilli (usually not more than 1/ml) were found in the milk samples, and were identified asLactobacillus plantarum, L. casei, L. brevis, L. fermentiand unclassified strains. In addition,Pediococcus cerevisiaeand leuconostoc species were isolated on the selective medium used, the leuconostocs occurring more frequently than either the lactobacilli or the pediococci. The lactic-acid bacteria in the cheese varied considerably, both quantitatively and qualitatively. Although in general the same species of organisms were isolated from the cheese as from the milks, the relative frequencies of occurrence were not the same, leuconostocs being found much more often in milk than in cheese, andL. plantarumandL. caseimore frequently in cheese. No association between numbers or types of lactic-acid bacteria and flavour of the cheese was noted, nor did the season of the year or the ration fed to the milking herd affect the lactobacillus flora of the milk.