Differential Growth of Listeria monocytogenes and Salmonella enterica Serovar Typhimurium in Sterile Juice from Fresh-cut Produce

Introduction: Ability of bacterial growth on fresh-cut produce under temperature abuse conditions is a food safety concern. Exudate material from fresh cut produce is often implicated as a supplementing factor for bacterial growth, particularly the growth of pathogens associated with foodborne illness. This study focused on evaluating the growth of foodborne pathogens in the juice of several produce commodities.

Purpose:  The purpose of this study was to evaluate the potential for growth by Listeria monocytogenes and Salmonella enterica in the sterile juice extracted from several fresh cut produce commodities.

Methods:  Juice was extracted from various fresh-cut produce commodities (including cabbage, pineapple, green pepper, cucumber, tomato, radish, carrot, broccoli, onion, romaine lettuce, celery and cantaloupe) and sterilized by filtration through 0.22 μm filters. Overnight cultures of S. enterica and L. monocytogenes were starved, inoculated into produce juices, and incubated for 24 hours at 37°C in a microplate reader. Bacterial growth (absorbance at OD 600) was measured over a period of 24 hours. Samples were also plated after 24 hours of incubation to estimate the bacterial population, with a detection limit of 1.7 log CFU/ml. The total proliferation was determined by comparing the population at the end of growth to that of the inoculum.

Results:  Results found the overall population growth of S. enterica in the produce commodities tested was significantly higher than the growth of L. monocytogenes (P<0.01). Differential results show that S. enterica grew better in juice extracted from tomato than L. monocytogenes. Neither bacteria showed significant growth in the juice of cabbage, onion, broccoli, and pineapple.

Significance:  This information can be used to evaluate the potential for growth of bacterial pathogens on fresh cut produce during processing and storage.