Impact of fresh-cut onion types and flavonoid profiles on the survival kinetics of foodborne pathogen during refrigerated storage

This study investigated the effect of onion flavonoid profiles on the growth, survival, and/or death kinetics of foodborne pathogens in fresh-cut onions at 4 °C. Fresh-cut white, yellow, red, and sweet onions were inoculated with separate four-strain cocktail(s) of nalidixic acid-adapted Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes achieving a 4 to 5 log CFU g⁻¹. The samples were stored in clam shell containers at 4 °C and 70 ± 2 % relative humidity for 14 days. Additionally, flavonoid profiles were determined on uninoculated control samples stored under similar conditions using standard chromatography techniques, with quercetin derivatives identified as the predominant flavonoids. Results indicated significant differences in pathogen reduction and survival across onion types. Salmonella and E. coli O157:H7 populations declined by 2 to 4 log after 14 days, while L. monocytogenes populations increased on white and red onions, remained stable on yellow onions, and declined on sweet onions. Red onions contained the highest flavonoid concentrations, followed by sweet, yellow, and white onions. Notably, despite having similar flavonoid levels, sweet onions showed greatest reduction of tested pathogens than red onions, suggesting that factors beyond flavonoid content may contribute to pathogen reduction. These findings provide new insights into the behavior of foodborne pathogens in fresh-cut onions and highlight the potential for flavonoids to influence pathogen survival during refrigerated storage.