Organic acids microbial inhibition

The CHARM inhibition assay (CIA), Charm farm test (CFT), and Valio TlOl test are all simple multiresidue screening tests based on microbial inhibition (34, 35). The CIA test is actually a disc assay using Bacillus stearothermophilus and specially formulated agar media to increase the sensitivity to sulfonamides. The CFT is a tube assay using the same test organism in a specific formulation, which, along with the nutrients, is in a tablet form. To roughly identify penicillins and sulfonamides with the CIA and CFT tests, positive samples should be reanalyzed after the addition of penicillinase and p-aminobenzoic acid. 

Organic acids may exhibit other sensory properties. For example, citric acid possesses sweet-and-sour sensory notes, and succinic acid has a salty-bitter taste. On the other hand, the typical taste and flavor of Emmental cheese can be ascribed to the propionic acid and a few other compounds, such as proline. In fact, taste and flavor result from the combination of different food constituents in definite proportions. Raw meat smells much like lactic acid, which arises from postmortem anaerobic glucolysis and determines the pH of meat, its final properties, and microbial stability. This same organic acid has been related to the inhibition of certain pathogenic bacteria in yogurt (3). Table 1 lists the reported threshold concentrations for various organic acids in different media (4-6). 

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,... 

Comparison of different inhibitory effects of an antimicrobial agent on microbial activity necessitates the determination of parameters that could express the influence of a toxic compound (Banerjee and Sarkar, 2004). Two such parameters have been identified kir which is the exponential inhibition constant, and is inversely correlated with tolerance to antimicrobials, and C50%, which refers to the toxic concentration that would inhibit 50% of any pysiological mechanism (Liewen and Marth, 1985 Banerjee and Sarkar, 2004). To form a good picture of the action of organic acids k, should be taken into account together with xmin values, in order to evaluate the inhibition of fermentation. However, the value of the reciprocal of k, plus the value of xmin could be adapted if needed, for example, for a more practical industrial approach. There is a fair correlation between k, and C50o/o. It is, however, easier to determine the latter parameter, and it... 

The effects of organic acids in the intestinal tract are two-fold. They reduce pH in the stomach and small intestine. Moreover, acid dissociation in the bacterial cell and the accumulation of salt anions inhibit microbial growth. 

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