Investigating the Antibacterial Effect of a Novel Gallic Acid-Based Green Sanitizer Formulation

The purpose of the present study was to investigate the mechanism of action of our newly developed green sanitizer formulation comprising a natural phenolic compound, gallic acid (GA), strengthened by the Generally Recognized as Safe (GRAS) materials hydrogen peroxide (H₂O₂) and DL-lactic acid (LA). Combining 8 mM GA with 1 mM H₂O₂ resulted in an abundant generation of reactive oxygen species (ROS) and a bactericidal effect towards Gram-negative (<i>Escherichia coli</i>, <i>Pseudomonas syringae</i>, and <i>Pectobacterium brasiliense</i>) and Gram-positive (<i>Bacillus subtilis</i>) bacteria (4 to 8 log CFU mL^-1 reduction). However, the exposure to this dual formulation (DF) caused only a modest 0.7 log CFU mL^-1 reduction in the Gram-positive <i>L. innocua</i> population. Amending the DF with 20 mM LA to yield a triple formulation (TF) resulted in the efficient synergistic control of <i>L. innocua</i> proliferation without increasing ROS production. Despite the inability to grow on plates (>7 log CFU mL^-1 population reduction), the TF-exposed <i>L. innocua</i> maintained high intracellular ATP pools and stable membrane integrity. The response of <i>L. innocua</i> to TF could be qualified as a "viable but nonculturable" (VBNC) phenomenon, while with the other species tested this formulation caused cell death. This research system may offer a platform for exploring the VBNC phenomenon, a critical food safety topic.