Quantitative structure activity relationship for the effect of benzoic acids, cinnamic acids and benzaldehydes on Listeria monocytogenes

The inhibition of a cocktail of 18 strains of Listeria monocytogenes by 24 mono-, di- and tri-substituted benzoic and cinnamic acids and 16 benzaldehydes was evaluated using the concentration (C) required to give a 50% growth inhibition under anaerobic conditions at 35 degrees C and pH 6.2 as a measure of biological activity (BAV), Using the method of least squares, multiple regression equations were obtained which described the contribution of some physicochemical and other structural properties of the compounds to their biological activity. The equation that best described the activity of benzoic and cinnamic acids was Log(1/C) = 3.54logK + 0.93pK(a) - 6.42, where K is a lipophilicity parameter determined by RP-HPLC and the effect of ionization is represented by pK(a). Benzaldehydes behaved differently, their activity being best described by the equation Log(1/C) = -0.23V(w) - 0.441/E(s)(o) + 0.25, where the activity is controlled by a steric parameter, the van der Waals volume (V-w), and an electronic-steric parameter for ortho substituents. Absence of a lipophilicity parameter indicates that partitioning into the cell membrane might not be required for antimicrobial activity. The models were tested in several food systems which showed that in food with a high protein or lipid content antilisterial activity was much lower than predicted, making the models unacceptable in such circumstances.