Efficacy of Lactobacillus plantarum on the Reduction of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on Fresh-cut Granny Smith Apple Slices

Introduction: Minimally processed fruits are often peeled, cut, or diced which compromise the fruits’ natural protective barriers, exposing a nutrient-rich medium and providing an ideal environment for the growth of microorganisms, including foodborne pathogens.  Recent outbreaks associated with minimally processed fruits indicate additional measures are needed to improve product safety.  Application of biological control agents postharvest could provide an additional hurdle to the growth of foodborne pathogens. 

Purpose: The purpose of this study was to evaluate the efficacy of Lactobacillus plantarum against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on fresh-cut apple slices.

Methods: Apple slices inoculated with E. coli O157:H7, L. monocytogenes, and Salmonella spp. (10⁴ CFU/g) were treated with L. plantarum (10⁷ CFU/g).  Apples were stored at 4°C and 20°C for seven and five days, respectively. Population means and standard deviations of treatment groups were determined. One way analysis of variance (ANOVA) and Tukey pairwise comparison were used to determine if there was a difference between treatments (α = 0.05).

Results: Populations of L. plantarum were maintained throughout storage at a concentration of 7.0 ± 0.4 log CFU/g at 4°C and 20°C. Populations of E. coli O157:H7, L. monocytogenes, and Salmonella spp. inoculated alone were not significantly different than populations treated with L. plantarum at 4°C. Populations of E. coli O157:H7, L. monocytogenes, and Salmonella spp. co-inoculated with L. plantarum were approximately 1.9 log CFU/g, 3.2 log CFU/g, and 0.5 log CFU/g less than populations inoculated alone after one, three, and five days of storage at 20°C.

Significance:  Application of L. plantarum on fresh-cut apples could potentially provide a hurdle to the growth of foodborne pathogens.