Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2022
Publication Date: 8/7/2022
Citation: Wang, L., Fan, X., Gurtler, J. 2022. Reduction of Salmonella enterica Typhimurium populations and quality of grape tomatoes treated with dry and humidified gaseous ozone. Postharvest Biology and Technology. 193, November 2022, 112061.
Interpretive Summary: Outbreaks of foodborne illnesses and recalls associated with fresh produce continue to occur in recent years. Effective intervention technologies to inactivate foodborne pathogens are needed. Ozone, as an FDA-approved oxidizer, can result in severe damage to the quality of fresh produce. The present study evaluated the impact of humidity during ozone treatment on the efficacy of ozone against Salmonella and on changes in quality of tomatoes during storage. Tomatoes with and without inoculated Salmonella on the stem scar and smooth surface were treated with various concentrations of gaseous ozone at two humidities (4% and 90%). Salmonella reductions were assessed immediately after treatment while quality was evaluated during 21 days of storage at 10 degrees C. Results demonstrated that increasing the relative humidity during ozone treatment not only increased the efficacy of ozone against Salmonella on tomatoes, but also minimized the ozone-induced deterioration in sensory and nutritional quality of the fruit. This information is of value for the produce industry to implement the technology to preserve the quality of fresh produce while enhancing microbial safety.
Technical Abstract: The present study was conducted to investigate the effect of humidity on the gaseous ozone inactivation of Salmonella enterica on grape tomatoes, and on the ozone-induced changes in fruit quality. Grape tomatoes were inoculated with Salmonella Typhimurium on the smooth surface and stem scar areas. The inoculated and uninoculated fruit (for quality studies) were treated for 1 h with 0, 800, 1,600 and 3,200 ppm gaseous ozone at two humidities: ca. 4% (dry) and 90% (humidified). Salmonella survival populations were determined immediately for the inoculated fruits while appearance, off-odor, texture, firmness, color, ascorbic acid and lycopene content, oxygen radical absorbance capacity values, and total phenolic content were analyzed on the uninoculated fruit during 21-days of storage at 10°C. Results demonstrated that, on the smooth surface, populations of Salmonella treated with 800, 1,600, and 3,200 ppm dry ozone were reduced by 0.1, 0.6 and 3.3 log CFU/fruit, respectively, while the corresponding humidified ozone reduced the populations by 3.2, >4.8 and >4.8 log CFU, respectively. On the stem scar area, 800, 1,600 and 3,200 ppm humidified ozone treatment reduced the Salmonella populations by 1.4, 2.3 and 4.7 log CFU/fruit, respectively, while the dry ozone treatments reduced the populations by 0.0, 0.5 and 1.9 log, respectively. On most sampling days during storage, fruit treated with 3,200 ppm and, frequently, 1,600 ppm dry ozone had significantly lower appearance scores, a*/b* values (redness), firmness, and ascorbic acid content than the control. When the fruit was treated with humidified ozone, the ozone-induced quality changes were negated. Our results demonstrated that, compared with dry ozone, humidified ozone had two benefits: (1) increased efficacy against Salmonella, and (2) reduced damage to fruit quality. The mechanisms for the observed phenomena are discussed in terms of water-ozone interaction and gas diffusion.