Purpose: This study aimed to determine whether H2O2 is generated on the surface of produce following application of solutions of the generally recognized as safe (GRAS) compounds gallic and benzoic acids, and UV-exposure.
Methods: Harvested tomato fruit and romaine lettuce leaves in pots were immersed in 10 mM solutions of gallic acid, benzoic acid, or water (control). The photosensitizer-treated tomatoes and lettuce were exposed to visible light in a plant growth chamber for 16 h light at 25°C and 8 h darkness at 18°C. Produce was analyzed for H2O2 production after 4 h and 24 h using the FOX (ferrous ion oxidation in presence of xylenol orange) assay. Change in absorbance due to H2O2 presence was measured at 560 nm using a spectrophotometer. Color change of produce was also evaluated after the treatments.
Results: H2O2 production measured after 4 h on tomato fruit that was treated with benzoic acid resulted in an OD560 of 0.69±0.11, and was significantly higher than the water control (P<0.05). Exposure of tomato to gallic acid resulted in an OD560 of 0.34±0.09 after 4 h, which was similar to the control. After 24 h, levels had returned to baseline. Lettuce treated with benzoic acid resulted in OD560 of 0.27±0.02 and 0.26±0.03 after 4 and 24 h, respectively, exhibiting no increase in H2O2 generation relative to the control. No impact on color change or visual quality in tomato occurred after treatments. Deterioration in lettuce quality was observed following benzoic acid, but not gallic acid treatment.
Significance: Benzoic acid application to tomatoes followed by UV exposure generated the antimicrobial compound H2O2 without compromising tomato quality.