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The present study shows the effect of UV processing on ascorbic acid, a key vitamin found in many fruit juices. Process developers and researchers can use this study as a model for designing experiments to identify factors that influence the stability of vitamin C and other bioactive compounds during UV processing.

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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 (>3log(CFU/mL) in 2,000 mg O 2 /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 predominantly responsible for the observed antimicrobial effect. The UV-A+GA treatment was also found to be effective in causing more than 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.

Possible mechanisms behind the enhanced antimicrobial activity of gallic acid (GA) and its ester propyl gallate (PG) in the presence of UV-A light against Escherichia coli O157:H7 were investigated. GA by itself is a mild antimicrobial and has a pro-oxidant ability. We found that the presence of UV-A light increases the uptake of GA by the bacteria. Once GA is internalized, the interaction between GA and UV-A induces intracellular ROS formation, leading to oxidative damage. Concurrently, GA + UV-A also inhibits the activity of superoxide dismutase (SOD), magnifying the imbalance of redox status of E. coli O157:H7. In addition to ROS induced damage, UV-A light and GA also cause injury to the cell membrane of E. coli O157:H7. UV-A exposed PG caused oxidative damage to the cell and significantly higher damage to the cell membrane than GA + UV-A treatment, explaining its higher effectiveness than GA + UV-A treatment. The findings presented here may be useful in developing new antimicrobial sanitation technologies for food and pharmaceutical industries.

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