Purpose: Evaluate the effect of current postharvest practices used at commercial fruit packing facilities on the contamination and persistence of L. monocytogenes in intact apples.
Methods: Freshly harvested Granny Smith apples and two L. monocytogenes outbreak strains linked to caramel apples were evaluated. To imitate apple contamination during dump-tank washing, fruits were immersed into contaminated water (6 log CFU/ml) to various depths (surface, 1 and 2 feet) for 20 min. To track water uptake by apples, Acid Blue 9 dye (100 mg/ml) was dissolved in the water. Seven days after inoculation, detection and enumeration of L. monocytogenes internalized into different areas of the apple fruit core was conducted following FDA-BAM protocols.
Results: Dye infiltration into apple core was observed from both calix and stem ends of the fruit. Under experimental conditions L. monocytogenes internalized into inner calix and stem areas of the apple core during the dump tank washing. One week after inoculation bacterial populations in inner core ranged from 1 to 3 log CFU/g. The incidence of L. monocytogenes infiltration significantly (P≤0.5) varied among treatments and was 52.1, 65.0 and 81.6% for the surface, 1 and 2 feet for immersed apples, respectively. No difference in L. monocytogenes infiltration incidence was observed between calix and stem inner sinuses of Granny Smith apples.
Significance: Identification of postharvest practices potentially facilitating contamination and survival of L. monocytogenes in apples will permit prevention of future recalls and outbreaks of foodborne listeriosis associated with consumption of pome fruits.