Synergistic Antimicrobial Effect of UV-A Irradiation and Malic Acid Combination Treatment Against Foodborne Pathogens on Spinach and the Underlying Mechanism

Introduction The objectives of this study were to evaluate the synergistic antimicrobial effect of ultraviolet A (UVA) and malic acid (MA) combination treatment against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach and to elucidate the mechanisms underlying the synergistic antimicrobial effects. Methods The cocktail of three pathogens was inoculated on the spinach leaves. The inoculated spinach leaves were treated with UVA, 0.5% MA, or UVA-MA combination for 0, 20, 40, and 60 min. Additionally, we investigated the effects of this combination treatment on spinach quality. Results Treatment with UVA-MA for 60 min decreased the cell counts of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 2.87-, 3.29-, and 6.41-log CFU/mL, respectively, which were attributed to the synergistic effect. Five mechanistic investigations revealed that the key mechanisms underlying the synergistic antibacterial effect of UVA-MA were cell membrane damage and intracellular reactive oxygen species (ROS) production. Treatment with UVA-MA for 60 min did not adversely affect the color, total phenol content, and texture of spinach. Conclusions These results suggest that the UVA-MA combination treatment can be an alternative strategy to conventional disinfection methods for ensuring the microbial safety of fresh produce.

Automated summary

This study evaluated the synergistic antimicrobial effect of UVA and MA combination treatment against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach, and elucidated the mechanisms underlying the synergistic antimicrobial effects, which were cell membrane damage and intracellular reactive oxygen species (ROS) production.