Effect of lactic acid concentration on growth on meat of Gram-negative psychrotrophs from a meatworks.

The inhibitory effect of the lactic acid in meat on gram-negative psychrotrophs appears to be due mainly to the decrease in pH, not to action of the undissociated acid. Species of Pseudomonas were essentially unaffected by the pH of normal meat. Other gram-negative psychrotrophs isolated from a meatworks included a large number of strains which would not grow on meat of normal pH at chill temperatures. Raising either the pH or the incubation temperature allowed many of the pH-sensitive strains to initiate growth. However, the growth rates of pH-insensitive strains were not affected by increasing the pH, and there were no significant differences in the composition of the spoilage floras which developed on chilled meat of normal and high pH.