Results confirm that the undissociated acid is the active antimicrobial species.
The effect could account for the stability of vegetable fermentations where no starter culture is used and asepsis is not observed. Keywords Acetic acid, automated optical density monitoring, E. coli, lactic acid, lactic fermen tation, Salmonella enteritidis. Introduction Acetic and lactic acids, generated microbiologically in situ or exogenously, are tra ditional means of improving food safety and shelf-life. Their antimicrobial action appears to be the result of the ability of the lipophilic, undissociated acid molecules to penetrate the bacterial plasma membrane. The antimicrobial effect of an organic acid will therefore depend upon its pK a value and the pH of the external medium.