Type of tomatoes and water rinse affect efficacy of acid washes against salmonella enterica inoculated on stem scar areas of tomatoes and on product quality

Authors: Fan, Xuetong; Gurtler, Joshua; Sokorai, Kimberly

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2018
Publication Date: 5/12/2018
Citation: Fan, X., Gurtler, J., Sokorai, K.J. 2018. Type of tomatoes and water rinse affect efficacy of acid washes against salmonella enterica inoculated on stem scar areas of tomatoes and on product quality. International Journal of Food Microbiology. 280:57-65.

Interpretive Summary: Consumption of raw tomatoes has been implicated in multiple Salmonella outbreaks in the U.S. in recent years. ARS researchers have previously shown that washing large round tomatoes with combinations of organic acids reduced populations of Salmonella by 99.999% on the stem scar area of large round tomatoes where bacteria often reside. However, the impact of the acid washes on fruit quality and their efficacy on grape tomatoes have not been studied. In the present study, we evaluated the changes in fruit quality after acid washed and compared two types of common tomatoes in response to the treatments. Our results demonstrated that the treatments were more effective in reducing populations of Salmonella on stem scar area of large round tomatoes than on the small grape tomatoes, and the water rinse after acid treatments negated residual acidic odor caused by the acid wash treatments. Therefore, tomato fruits may be washed with organic acids followed by rinsing with water to enhance microbial safety of tomatoes while maintaining fruit quality.

Technical Abstract: The study was conducted to evaluate the effects of post-treatment rinsing with water on the inactivation efficacy of acid treatments against Salmonella inoculated onto stem scar areas of two types of tomatoes. In addition, impact on fruit quality was investigated during 21 days post-treatment storage at 10 degrees C. A four-strain cocktail of Salmonella enterica (S. Montevideo, S. Newport, S. Saintpaul, and S. Typhimurium) was inoculated onto stem scar areas of grape and large round tomatoes. The inoculated fruits were then treated for 2 min with the following solutions: water, 2% lactic acid + 2% acetic acid + 2% levulinic acid, 1.7% lactic acid + 1.7% acetic acid + 1.7% levulinic acid, and 3% lactic acid + 3% acetic acid. After treatments, half of the fruits were rinsed with water while another half were not rinsed. Non-inoculated grape tomatoes for quality analysis were treated with the same solutions with and without subsequent water rinse. Results showed that the acid combinations reduced populations of Salmonella enterica on the stem scar area of grape tomatoes by 1.52-1.90 log CFU/fruit, compared with the non-treated control while water wash and rinse removed the bacterium by only 0.23-0.30 log CFU/fruit. On the stem scar of large round tomatoes, the same acid treatments achieved 3.54 log CFU/fruit reduction of the pathogen. The different response to the acid washes between grape and large round tomatoes seems to correlate with the differences in surface characteristics of stem scar areas observed with SEM. Rinsing with water after acid combination treatments did not significantly affect the efficacy of the treatments in either grape or large round tomatoes. Acidic off-odor was detected on fruits treated with acid combination without water rinse 1 day after treatment while water rinse eliminated the off-odor. The acid treatments with and without water rinse did not consistently affect appearance, color, firmness, or lycopene or ascorbic acid contents of tomatoes during 21-days storage at 10 degrees C. Considering the nondifference in antimicrobial efficacy against Salmonella between the fruits with and without water rinse following acid treatments, and the elimination of acidic odor by water rinse, fruits should be rinsed with water after acid treatments.