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Quantitative Assessment of the Presence of Salmonella and Fecal Indicators in Mexican Tomatoes for Export to the United States
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Over the past decades, there has been increase in the consumption of the fresh tomato in the United States; this has been attributed to the nutritional benefits of fresh tomato, its widespread use in cooking and its availability throughout the year. In a Food and Agricultural Organization report, the United States was ranked as one of the largest producers of the fresh tomato in the world. In spite of its large production capacity, large quantities of the tomatoes are still being imported to the United States annually from Mexico. Series of multistate outbreaks of Salmonella infection have been associated with consumption of the fresh tomatoes; traceback of the tomatoes implicated in salmonellosis has been traced to tomatoes grown domestically. However, a survey conducted by U.S. Department of Agriculture on both domestic and imported tomatoes determined that imported fresh tomato was Salmonella positive. The purpose of this study was to determine the microbiological quality of fresh tomatoes imported from Mexico to the United States. The study consisted of sampling surfaces of cleaned tomatoes in Mexico prior to packing and shipping to the United States, and sampling of the tomato wash water at the end of the work shift at a Mexican tomato packinghouse. Four tomatoes were randomly sampled prior to packing, and they were rinsed with Universal Preenrichment Broth (UPB), this was repeated 10 times per working shift, with 2 shifts per day. 102 l of tomato wash water were collected and sampled with the aid of Modified Moore’s Swab (MMS) and membrane filter. The tomato wash water was collected at the end of shift twice daily. Both fruit and wash water samplings were repeated 3 times during the tomato harvesting season. Both the tomato UPB rinsates and the membrane filter were assayed for the E. coli and enterococci populations. Additionally, the tomato UPB rinsates and MMS were assayed for the presence of Salmonella. The results of the microbiological analysis on the UPB rinsates showed that no Salmonella was present, E. coli was not detectable (< 1.0), and the mean populations of enterococci were log 3.8, 2.6, and 1.0 CFU/g in sampling trials 1, 2, and 3 respectively. In the tomato wash water, no Salmonella was present, and no E. coli and enterococci were detected. Therefore, it was concluded that the microbiological quality of the tomatoes that were sampled and tested were high, this was due to the fact that all the samples collected tested negative to Salmonella analysis, and no E. coli was detected in any of the samples.
Onafowokan, Ayoola A (2013). Quantitative Assessment of the Presence of Salmonella and Fecal Indicators in Mexican Tomatoes for Export to the United States. Master's thesis, Texas A&M University. Available electronically from