Enhancing Antimicrobial Efficacy of Sodium Benzoate

S. Foster, P. Rempala, D. Mueller, L. Dornan, A. Yarnell, J. Blankenship

In many cleaning product applications in the market place, the inclusion of sodium benzoate as a stand-alone preservative is providing sufficient microbial control. It was observed that inclusion levels are typically lower, resulting in economical use and, consequently, feasibility in a wider pH range of cleaning products compared to what was generally believed. For sodium benzoate
to effectively preserve, formulations require sufficient concentrations of the undissociated organic acid, which is benzoic acid. The acid equilibrium constant (pKa) of benzoic acid determines the degree of acid dissociation, and a larger value would result in increased benzoic acid concentrations. Titrations show that in the presence of home care surfactants, the apparent pK’a increases as surfactant concentration increases, indicating a higher concentration of the active substance. This was confirmed with 13CNMR. Microbial challenge testing was performed to verify that the increased apparent pK’a yields increased antimicrobial efficacy. A surfactant was selected to increase the benzoic apparent pK’a with substantial improvements in microbe reductions versus controls. Finally, a theoretical model based on surfactant properties was adopted to explain the observed pK’a increases. This model provides a basis for detailed formulation advice and justification to the enhanced antimicrobial efficacy of Kalaguard® SB sodium benzoate.
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