Effectiveness of a Spontaneously Emulsified Carvacrol Nanoemulsion Acidified with Organic Acids against a Salmonella Species Cocktail on Contaminated Mung Beans

Introduction: Outbreaks of foodborne illness from the consumption of sprouts has been linked to contaminated seeds prior to germination. Currently, the recommended treatment involves soaking seeds in 20,000 ppm hypochlorite for 15 – 25 min prior to germination. In this study, an alternative treatment involving soaking Salmonella spp. coated mung beans in an acidified carvacrol nanoemulsion was tested.  

Purpose: The purpose of this study was to evaluate the effectiveness of a novel, food-grade, and label friendly treatment on contaminated sprouting seeds. 

Methods: Mung beans were inoculated to levels of approximately 8, 5, 4, or 3 log CFU/g of seed and treated by soaking inoculated seed batches in acidified (acetic or levulinic acid) nanoemulsion (4,000 or 8,000 ppm) for 30 or 60 min. Numbers of surviving cells were determined after treatment by suspending seeds in broth and performing plate counts and/or Most Probable Number enumeration. Treated seeds were sprouted and tested for the presence of the pathogen.

Results: In the mung bean system, levels of Salmonella spp. were reduced by 5 log, regardless of concentration and/or treatment time when compared to the control or organic acids alone.  When seeds were inoculated at either 4 or 3 log CFU/g seed, pathogens were not detected in mung bean sprouts grown from acidified carvacrol nanoemulsion treated seeds, regardless of treatment concentration or time.  

Significance: These results show that the use of the acidified carvacrol nanoemulsion may be an alternative, food-grade, and label friendly antimicrobial treatment for mung beans.