Inactivation of Salmonella in grape tomato stem scars by organic acid wash and chitosan-allyl isothiocyanate coating

The objective of this study was to evaluate inactivation of inoculated Salmonella enterica on grape tomato stem scars exploiting integrated treatment of organic acid wash (AW) followed by chitosan-allyl isothiocyanate (CT-AIT) coating. The treatment effect on microbial loads and fruit quality during 21 days storage at 10 °C was also determined. A bacterial cocktail containing three serotypes of Salmonella enterica was used for this study based on their association with produce-related outbreaks. Tomatoes were spot inoculated on stem scars and then immersed in an organic acid solution (700 ml) containing 0.5% (v/v) each of acetic (AA) and formic acid (FA) to wash under mild agitation for 1 min at ambient temperature (22 °C) followed by 1 min dipping in a coating solution containing 6 ml AIT/g CT. AW in 0.5% organic acid (AA + FA) for 1 min reduced Salmonella population by 2.7 log CFU/g from an initial load of 7.8 log CFU/g, while additional coating treatment of AW tomatoes reduced the pathogens on stem scars to undetectable levels (< 0.7log CFU/g), achieving, in combination, a > 7 log CFU/g reduction for the pathogen. Although the populations of Salmonella in the controls (approx. 7.8 log CFU/g stem scar) did not change significantly during 21 days of storage at 10 °C, the populations were reduced to undetectable level in the integrated (AW plus CT-AIT) treated stem scars on day 1 and no regrowth was observed during storage. The treatment significantly (p < 0.05) reduced background bacterial loads to approx. 1.3 log CFU/g and the population remained unchanged through day 21 at 10 °C. The treatment also completely inactivated mold and yeast on day 1 with no growth reoccurrence. These results indicate that the integrated treatment can provide a safe and effective intervention strategy for grape tomatoes.