Enhancing gallic acid antimicrobial activity against Escherichia coli by ultraviolet-C light irradiation

Abstract

This study aimed to evaluate the UV-C light effect on enhancing the antimicrobial activity of gallic acid (GA) against Escherichia coli at different initial microbial loads. The highest microbial reduction (3.08 ± 0.09 log) was attained at low microbial load after 10-min contact with irradiated GA (IGA). Increasing the initial microbial load (6–7 × 107 CFU/mL) reduces the IGA effect. Application of the IGA (0.015 M) in combination with UV-C light (15 min) caused lethal injury in E. coli at a low microbial load. Furthermore, at a low microbial load, a contact time of 5 min and 0.15 M was enough to reach >5-log reductions, whereas, at high microbial concentrations, the maximum GA concentration (0.25 M) was necessary to achieve the same inactivation. Increasing GA concentration, irreversible microbial damage was observed, with no microbial growth in samples treated for 10 min with IGA at 0.10–0.25 stored at 22 °C. Industrial relevanceGA is a phenolic compound with limited antimicrobial activity. However, the UV-C light treatment enhances its antimicrobial activity, increasing its application as a disinfectant of surfaces, instruments, and fresh food products, among other applications currently demanded by the consumers and food industry. In this sense, IGA can be used as a disinfectant agent for fruit and vegetables, in combination with novel or traditional technologies as a combined methodology to reduce the microbial load, or even as a preservative to maintain the microbial load during storage.