Synergistic interaction of ultraviolet light and zinc oxide photosensitizer for enhanced microbial inactivation in simulated wash-water

Synergistic interaction of ultraviolet light (UV-A) and zinc oxide (ZnO) was investigated for enhanced inactivation of Escherichia coli BL21 and T7 bacteriophage in simulated wash-water. In the absence of organic content, UV-A (9.53 J/cm(2)) and 1 mM ZnO alone caused 3.9 and 0.7 log CFU/mL reductions respectively in logarithmic phase bacteria after 60 min, while a combined treatment caused 6 log CFU/mL reductions. Stationary-phase bacteria were more resistant and a combined treatment caused only 3.5 log CFU/mL reductions. Organic matter in the wash-water lowered the inactivation rates. Nevertheless, approximately 2-log reductions were observed at the highest organic load. T7 bacteriophage was not sensitive to UV-A alone. However, 1 mM photo-irradiated ZnO caused 6.00 log PFU/mL reductions after 60 min. Bacteriophage inactivation was also significantly lowered by organic matter. The reactive oxygen species generated from photo-irradiated ZnO were responsible for the microbial inactivation. UV-A irradiated ZnO is an attractive sanitation approach for fresh-produce washing. Industrial relevance: Chlorine-based sanitizers that are conventionally used for washing fresh-produce suffer significant limitations including occupational hazard for workers from over-exposure to chlorine and safety hazards to the population due to formation of chlorinated organic matter. This study highlights that UV-A irradiated ZnO is a promising alternative to sanitize wash-water and fresh-produce and reduce the risk of bacterial as well as viral cross-contamination. Future studies are needed to optimize and scale-up this process for industrial use. (C) 2015 Elsevier Ltd. All rights reserved.