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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL FOOD SAFETY OF FRESH AND FRESH-CUT PRODUCE Title: Effects of tomato variety, temperature differential and post-stem removal time on internalization of Salmonella Thompson into tomatoes

Authors
item Xia, Xiaodong -
item Luo, Yaguang
item Yang, Yang -
item Schneider, Keith -
item Meng, Jianghong -

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2011
Publication Date: February 2, 2012
Citation: Xia, X., Luo, Y., Yang, Y., Schneider, K., Meng, J. 2012. Effects of tomato variety, temperature differential and post-stem removal time on internalization of Salmonella Thompson into tomatoes. Journal of Food Protection. 75(2):297-303.

Interpretive Summary: Foodborne illness outbreaks associated with consumption of contaminated tomatoes have negatively impacted public health, consumer confidence in eating tomatoes, and the industry’s economic well-being. Reducing pathogen contamination and internalization is critical to ensure the food safety of tomatoes. Studies reported in this research examined in depth the pathogen internalization as impacted by tomato varieties, differential between the tomato pulp temperature and wash water temperature, and the time delay between harvesting and post-harvest water usage. The results provide important information for the industry and the FDA to develop science-based food safety standards and regulations to improve food safety of tomatoes.

Technical Abstract: Tomatoes have been implicated in several Salmonellosis outbreaks due to possible contamination through bacterial infiltration into tomatoes during post-harvest handling. The aim of this study was to determine the effects of tomato variety, dump tank water to tomato pulp temperature differential, and post-stem removal time on internalization of Salmonella Thompson into tomatoes, and the distribution of Salmonella inside tomatoes. Mature green tomatoes, tempered to 90 °F (32.2 °C), were immersed in water containing approximately 106 cfu/ml S. Thompson. Tomato varieties (Mountain Spring, Applause, BHN961), temperature differentials between tomato pulp and bacterial suspension (-10 °F, 0 °F, 10 °F), and the time between stem removal and bacteria suspension water immersion (0, 2h, 16h) on Salmonella internalization were evaluated. Internalization frequencies and cell density were determined by culture enrichment and most probable number methods, respectively. Overall, variety and post-stem removal time significantly affected the frequency of Salmonella internalization (P = 0.0001), while the temperature differential had no significant effect (P = 0.36). Mountain Spring was less susceptible to Salmonella internalization than that of Applause and BHN961. Delaying the time interval between stem removal and immersion greatly reduced Salmonella internalization in BHN961 and Applause, while it had no effect in Mountain Spring tomatoes. Furthermore, all internalized Salmonella were found within the core tissue segments underneath the stem-scars. This study provides valuable information for tomato industries to optimize conditions in packinghouses to better control Salmonella internalization, thereby reducing the risk of tomato-associated salmonellosis in humans.

Last Modified: 10/1/2014
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