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

A synergistic interaction between gallic acid (GA) and UV-A light (UV-A + GA) to inactivate E. coli 0157: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 0157:H7 in suspension in the absence (>5 log(CFU/mL)) and the presence of organic content (>3-log(CFU/mL) in 2000 mg O-2/L COD (Chemical Oxygen Demand) organic load), and resulted in similar to 80% decrease in the metabolic activity of E. coli 01.57: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 0157: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 0157:H7 on the surface of spinach leaves. UV-A + GA treatment can serve as an effective intervention in the fresh produce sanitation. Industrial relevance: The 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 0157: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. (C) 2016 Elsevier Ltd. All rights reserved.