Antimicrobial effect of synergistic interaction between UV-A light and gallic acid against Escherichia coli O157:H7 in fresh produce wash water and biofilm

•GA + UV-A inactivated 3.7 log(CFU/mL) E. coli O157:H7 in solution of 2000 mg/L COD.•GA can be reused in multiple cycles of continuous treatment without losing efficacy.•Catalase protected E. coli from the effect of photosensitized GA in suspension.•UV-A exposed GA inhibited the metabolic activity of E. coli O157:H7 biofilm by ~ 75%.•GA in suspension was absorbed by E. coli O157:H7 cells

A synergistic interaction between gallic acid (GA) and UV-A light (UV-A + GA) to inactivate E. coli O157:H7 in spinach wash water and in biofilm was evaluated. A 30-min exposure to UV-A light in presence of 10 mM GA had relevant biological effect in the inactivation of E. coli O157:H7 in suspension in the absence (> 5 log(CFU/mL) ) and the presence of organic content (> 3-log(CFU/mL) in 2000 mg O2/L COD (Chemical Oxygen Demand) organic load), and resulted in ~ 80% decrease in the metabolic activity of E. coli O157:H7 biofilm. GA solutions could be recycled through at least 3-cycles of UV-A treatment without a significant loss in antibacterial effect. Catalase reduced the extent of E. coli O157:H7 inactivation from the UV-A + GA treatment suggesting that generation of hydrogen peroxide was partially responsible for the observed antimicrobial effect. The UV-A + GA treatment was also found to be effective in causing > 3 log(CFU/mL) reductions in E. coli O157:H7 on the surface of spinach leaves. UV-A + GA treatment can serve as an effective intervention in the fresh produce sanitation.Industrial relevanceThe results of this study show that a synergistic interaction between gallic acid (GA) and UV-A (365 nm) light is an effective treatment for sanitation of fresh produce and water used to wash fresh produce. It was also found to be effective against the E.coli O157:H7 biofilm. The attractive attributes of this technology include a relatively low cost; specific, light-triggered activity; non-toxic nature and scalability. Thus, this technology has potential to replace conventional chemical sanitizer-based sanitation approaches.