Antimicrobial Effectiveness of Coating Solutions Containing Chitosan, Lauric Arginate Ester and Allyl Isothiocyanate against E. coli O157:H7 and Salmonella spp. on Strawberries

Introduction: An outbreak of hemorrhagic colitis in 2011 was associated with contaminated strawberries, which resulted in two deaths.  There is a need for a preservation technique that reduces pathogenic contaminants on fresh strawberries without compromising quality. In our previous studies, lauric arginate ester (LAE), allyl isothiocyanate (AIT) and organic acids were used for antimicrobial coatings and films, and were effective in inhibiting foodborne pathogens in ready-to-eat meat, shrimp, and cantaloupe. However, optimization of these coating formulations for strawberries has not been further investigated.

Purpose: This study was conducted to identify different coating formulations for inactivating E. coli O157:H7 and Salmonella spp. from artificially-inoculated strawberries.

Methods: Ten edible coating formulations were developed, which consisted of chitosan (1%), AIT (0, 1, 2 %), LAE (0, 1, 2%), organic acids (levulinic acid + lactic acid; 0.5, 1%), and an emulsifier (0.167, 0.5%). The coating solutions were high pressure homogenized and directly coated on the surface of strawberries inoculated with a six-strain composite of E. coli O157:H7 (ATCC 43895, ATCC 43894, and strain C9490) and Salmonella (Newport H 1275, St. Paul 02-517-1, and Stanley H0558). Strawberry samples were placed in PET boxes and stored at 4°C. Survival of E. coli O 157:H7 and Salmonella were determined after 1, 2, and 5 days of storage.

Results: All coatings containing AIT and LAE significantly (P<0.05) inactivated E. coli O157:H7 and Salmonella on the surface of strawberries stored at 4°C for 5 days. When the same concentrations were used, AIT showed significantly stronger antimicrobial activity than LAE. The coatings reduced pathogens by 1.5, 2.0, and 4.0 log CFU/strawberry in 1, 2 and 5 days, respectively. Higher concentrations of acids (1% vs. 0.5%) or emulsifiers (0.5% vs. 0.167%) did not show significant difference in antimicrobial activity.

Significance: Results from this study provide some options for decontaminating strawberries prior to serving to customers.