Characterization of the relationship between postharvest fungal rot and Listeria innocua die-off rates on Gala apples during long-term storage [Abstract]

Authors: HAMILTON, ALEXIS - Washington State University; RUIZ, BLANCA - Washington State University; MENDOZA, MANOELLA - Washington State University; Mattheis, James; HANRAHAN, INES - Washington Tree Fruit Research Commission; CRITZER, FAITH - Washington State University

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2021
Publication Date: 7/26/2021
Citation: Hamilton, A., Ruiz, B., Mendoza, M., Mattheis, J.P., Hanrahan, I., Critzer, F. 2021. Characterization of the relationship between postharvest fungal rot and Listeria innocua die-off rates on Gala apples during long-term storage [Abstract]. International Association for Food Protection. 84(5):49.

Interpretive Summary:

Technical Abstract: Introduction: Botrytis cinerea and Penicillium expansum can colonize and rot apple tissue as storage time increases, which may impact the growth of saprophytic foodborne pathogens like Listeria monocytogenes. Decayed apples are exposed to other co-mingled fruit and packing equipment and may serve as a source of contamination. Purpose: To determine population changes of Listeria innocua (LI) as a surrogate for L. monocytogenes on apples co-inoculated with Penicillium expansum (PE) or Botrytis cinerea (BC) during 11 months of controlled atmosphere cold storage conditions. Methods: Gala apples (n=540) were drenched in pyrimethanil and inoculated with Listeria innocua (LI) in two-6.25 cm2 spots on the equator, one of which was wounded. Apples were assigned to one of three treatments: LI-only or co-inoculation with BC or PE. Apples were treated with 1-methylcyclopropene and stored under controlled atmosphere conditions (1°C, 1% CO2/2% O2). LI population was determined at 1 week, and 1, 3, 6, 9, and 11 months. The inoculation site was excised, and cells eluted in 24 mL 0.1% peptone with 0.2% Tween 80, serially diluted, and plated on Modified Oxford Medium and incubated 48 h at 35°C. After three months, LI consistently fell below the limit of detection (1.35 log CFU/g) and samples were enriched following a modified BAM method with PCR confirmation. Results: Populations of LI decreased by up to 5.57 log CFU/cm2, with significant differences in populations based on wound status and treatment. LI survival was greater across timepoints on wounded surfaces (p<0.0001). LI survival was greater in LI-only and BC treatments for all but one time point on wounded surfaces (p<0.05). Significance: LI survival was dependent on wound status and fungal species, suggesting risk may depend on type of postharvest rot. Postharvest intervention strategies should emphasize removal of infected or punctured fruit as soon as possible before or during packing.