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

Authors: Mukhopadhyay, Sudarsan; Sokorai, Kimberly; Ukuku, Dike; Jin, Zhonglin; Fan, Xuetong; Olanya, Modesto; Juneja, Vijay

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2017
Publication Date: 1/20/2018
Citation: Mukhopadhyay, S., Sokorai, K.J., Ukuku, D.O., Jin, Z.T., Fan, X., Olanya, O.M., Juneja, V.K. 2018. Inactivation of Salmonella in tomato stem scars by organic acid wash and chitosan-allyl isothiocyanate coating. International Journal of Food Microbiology. 266:234-240.

Interpretive Summary: The microbial safety of fresh fruits and vegetables continues to be a major concern. Tomatoes, leafy greens, and melons have been frequently implicated in outbreaks of foodborne illness. Currently, produce industry relies on a chlorine based sanitizer wash. However, effectiveness of chlorine wash is limited and the effectiveness of chlorine reduces rapidly on contact with organic matter. Chlorine also reacts with carbohydrates on produce surface to form carcinogenic byproducts. Due to the severity of this problem there is a need for development of a safe and effective intervention strategy as an alternative to chlorine-based wash. Thermal treatment is not an appropriate method for decontamination since produce is very heat sensitive. The purpose of present study was to evaluate the combined or synergistic antimicrobial efficacy of an integrated method utilizing organic acid wash and chitosan-allyl isothiocyanate coating against Salmonella on stem scars of tomatoes.

Technical Abstract: The objective of this study was to evaluate inactivation of inoculated Salmonella enterica on 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 degrees 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 a mixture of organic acid solution (700 mL) containing 0.5% (v/v) acetic (AA) and formic acid (FA) to wash under mild agitation for 1 min at ambient temperature (22 degrees 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 greater than 5 log CFU/g reduction of the pathogen. Although the populations of Salmonella in the controls (ca. 7.8 log CFU/g stem scar) did not change significantly during 21 days of storage at 10 degrees 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 ca. 1.3 log CFU/g and the population remained unchanged through day 21 at 10 degrees 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 tomatoes.