The Efficacy of Chitosan Coating in Reducing Surface Attached Salmonella on Tomatoes

Introduction:   A microbial safety concern with tomatoes is related to several Salmonella outbreaks. Alternative and novel methods are needed to enhance the microbial safety of tomatoes following a standard chlorine wash step.  Chitosan is an edible, biodegradable, non-toxic and antimicrobial active compound. 

Purpose: In this study, the efficacy of chitosan to control Salmonella, yeast and mold, and commensal bacteria associated with tomatoes was evaluated. 

Methods:  Tomatoes (n = 172) were inoculated with Salmonella to achieve 10⁴ CFU/g. All tomatoes were dipped in 100 ppm chlorine water for 90 seconds. After drying, tomatoes were dipped in 0.2% chitosan solution for 90 seconds. Controls were not treated with chitosan. Post-treatment tomatoes were stored at 15°C and 80-90% humidity for 15 days. The population of commensal bacteria, Salmonella, yeast and mold were evaluated at pre-determined times. 

Results:  The initial population of commensal bacteria, Salmonella, yeast and mold were 5.65, 4.44 and 4.05 log CFU/g, respectively. Immediately post-treatment, a 4.02-log CFU/g reduction in commensal bacteria was achieved on treated compared to a 3.33-log CFU/g reduction on control tomatoes. Up to a 4-log CFU/g reduction in Salmonella was achieved compared to 3.25-log CFU/g reduction in control. Yeast and mold populations immediately post-treatment decreased by 2.43 log CFU/g, compared to a 1.93-log CFU/g reduction in control. By 24h post-treatment the population of commensal bacteria, Salmonella, yeast and mold increased to pre-treatment levels on both control and treated tomatoes and then remained constant through 15 days of storage.

Significance: Treatment of tomatoes with 0.2% chitosan effectively reduced populations of Salmonella, yeast and mold. These results serve as the base for development of a product that improves product safety and shelf life.