Synergistic photoinactivation of Escherichia coli and Listeria innocua by curcumin and lauric arginate ethyl ester micelles

Abstract

This study evaluated the changes in dispersibility in the aqueous phase, chemical stability, and antimicrobial activity of curcumin after being encapsulated in a lauric arginate ethyl ester (LAE) micelle. Stock curcumin-LAE solutions were prepared by titrating curcumin dissolved in ethanol into LAE aqueous solutions (pH 3.5). The LAE in the stock solutions inhibited the crystallization and prevented the chemical degradation of curcumin during storage at 20 °C. The antimicrobial activity of the curcumin-LAE solutions against Escherichia coli (E. coli) and Listeria innocua (L. innocua) cocktails was assessed by exposing the sample to UV-A light (λ = 365 nm) for 5 min. For samples with both LAE and curcumin at pH 3.5 during irradiation, synergistic antimicrobial activity was observed. The release of protein or nucleic acid from the cells indicated an increase in its membrane permeability after treatments which was due to LAE-facilitated interaction between the photosensitizer and the membrane. LAE could inactivate both bacteria within 10 min without UV-A light irradiation, only at pH 7, which shows that LAE's antimicrobial efficacy depends on the pH. Therefore, microbial inactivation by two mechanisms, photosensitization and permeability operating simultaneously, produced a curcumin-LAE solution that could inactivate bacteria at a broad pH range.