Analysis of the interactions of a cationic surfactant (lauric arginate) with an anionic biopolymer (pectin): isothermal titration calorimetry, light scattering, and microelectrophoresis

Abstract

Lauric arginate (LAE), a cationic surfactant, is a highly potent food-grade antimicrobial that is active against a wide range of food pathogens and spoilage organisms. In compositionally complex environments, the antimicrobial activity of cationic LAE is likely to be impacted by its interactions with anionic components. The purpose of this study was to characterize the interactions between cationic LAE and an anionic biopolymer (high methoxyl pectin, HMP) using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. ITC and ME measurements indicated that LAE bound to pectin, while turbidity measurements indicated that the complexes formed could be either soluble or insoluble depending on solution composition. In the absence of pectin, the critical micelle concentration (CMC) of LAE determined by ITC at 25 degrees C was 0.21% (w/v). The amount of LAE bound per unit amount of pectin decreased with increasing pectin concentration (from 1.5 to 0.5 g/g for 0.05 to 0.5 wt % pectin) and with increasing temperature (from 1.7 to 1.3 g/g for 15 to 40 degrees C). The binding contribution to the LAE-pectin interaction was exothermic and was attributed to electrostatic attraction between the cationic surfactant and anionic biopolymer. This study demonstrates that lauric arginate can form either soluble or insoluble complexes with anionic biopolymers depending on the composition of the system.