Physiological actions of organic acids

The antimicrobial effect and toxicity of organic acids have been attributed to (1) a combination of the hydrogen ion concentration (lowering the pH), (2) consequent decreases in proton motive force, and (3) the action of undissociated molecules that may freely permeate the cell membrane 

Most foodborne pathogenic bacteria are neutrophiles with their optimum growth pH ranging from pH 6-pH 7. These bacteria will only encounter acid-related stress in food systems as a result of the presence of lipid-permeable weak acids (Hill, O Driscoll, and Booth, 1995). 

Transporters for monocarboxylic acids include (1) the bacterial lactate permease LctP family, (2) eukaryotic proton-linked monocarboxylate transporter MCT family, and (3) monocarboxylate permease. These transporters contain no ATP binding cassette (ABC) motifs and are considered to transport monocarboxylic acids via a proton-coupled reaction (Nakano, Fukaya, and Horinouchi, 2006). 

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