Number of undissociated organic acids that enter the bacterial cell

1 Number of undissociated organic acids that enter the bacterial cell 

All three acids reduced pH to 3 in unbuffered H20, even at concentrations as low as 10 mM (Lind, Jonsson, and Schnurer, 2005). 

Organic acids can enter the microbial cell only in their undissociated forms, which diffuse across the microbial cell membrane. This entrance of the acid molecule then lowers the intracellular pH (pH,) of the cell (Carrasco et al., 2006). The concentration of the undissociated form of an organic acid and the pH of the environment are interdependent variables, linked by the Henderson-Hasselbach equation (Breidt, Jr., Hayes, and McFeeters, 2004). As the extracellular pH decreases, the number of undissociated organic acids increases, and so do their activities toward the microbial cells (Kwon and Ricke, 1998). This undissociated state of the acid molecule is primarily responsible for any antimicrobial activity and effectiveness is dependent on the dissociation constants (pKa) of the acid (Barbosa-Canovas et al., 2003). This undissociated state of the organic acid is extremely important in the capacity to inhibit a microbial cell (Gauthier, 

More than 10-20 x the level of dissociated acid is needed to achieve the same inhibition as for undissociated acid (Presser, Ratkowsky, and Ross, 1997). However, although the undissociated molecules generally have a greater inhibitory effect, studies have also shown that the total inhibitory action of the weak acid is dependent upon a combination of the effects that are produced by undissociated acid molecules as well as the dissociated ions (Ray, 1992 Liick and Jager, 1997 Taniguchi et al., 1998). 

The strengths of weak acids are measured on the pK, scale. The smaller the number on this scale is, the stronger the acid (Namazian and Halvani, 

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Antimicrobial action of organic acids is dependent on various factors. The following are discussed (Chaveerach et al., 2002) number of undissociated organic acids that enter the bacterial cell, acidity constant (piCa value), water activity (aw), temperature, and production of H202. 

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