Review Article - Growth and Survival of Listeria monocytogenes on Intact Fruit and Vegetable Surfaces during Postharvest Handling: A Systematic Literature Review

Does LM grow on the surfaces of produce?  A review article in the Journal of Food Protection surveyed research on the topic and provides insight into factors that affect growth on the surface including moisture, topography, nutrient availability, and microflora.   Some key items from the discussion:

• "Growth of foodborne pathogens on intact produce surfaces is less likely to occur compared with cut produce surfaces, owing to the protective outer barriers on most intact produce."  But once this outer barrier is damaged, then growth or survival is increased.  
• Surface topography, such as surface roughness, has also been found to influence bacterial attachment and retention to a surface 
• "Numerous studies have observed higher background microflora to inhibit or decrease pathogen growth rates."
• While growth varies with the type of produce, the impact of temperature also varies with the type of produce. However, "The combined data reported in this review suggest that storage temperature influences the growth and/or survival of L. monocytogenes on intact fruit and vegetable surfaces, with higher storage temperatures resulting in more L. monocytogenes growth. It should be noted that L. monocytogenes may still grow at refrigeration temperatures; however, data suggest a longer lag time before growth occurs (117), and several of the studies examined herein only carried experiments out to shelf time or less, allowing for the possibility of growth at refrigeration if kept beyond product shelf life." 
• While there was limited work done on relative humidity, "L. monocytogenes populations survived better at higher relative humidity compared with L. monocytogenes populations at lower relative humidity. Furthermore, this trend was more pronounced when intact produce was stored at cooler temperatures."  
• "Generally, environments with lower relative humidity may suppress L. monocytogenes growth and/or survival, especially if combined with temperature control strategies. This may be a  challenge for the produce industry because relative humidity can be difficult (and potentially expensive) to control in some produce environments along the supply chain."
• Table 3 provides a summary of the various studies for produce type and temperature.
  

Journal of Food Protection, Vol. 83, No. 1, 2020, Pages 108–128
Review
Growth and Survival of Listeria monocytogenes on Intact Fruit and Vegetable Surfaces during Postharvest Handling: A Systematic Literature Review
CLAIRE M. MARIK,1 JOYCE ZUCHEL,1 DONALD W. SCHAFFNER,2 AND LAURA K. STRAWN1*
1Department of Food Science & Technology, Eastern Shore Agricultural Research and Extension Center, Virginia Tech, Painter, Virginia 23420; and
2Department of Food Science, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA
MS 19-283: Received 15 June 2019/Accepted 19 September 2019/Published Online 19 December 2019
ABSTRACT

Listeria monocytogenes may be present in produce-associated environments (e.g., fields, packing houses); thus, understanding its growth and survival on intact, whole produce is of critical importance. The goal of this study was to identify and characterize published data on the growth and/or survival of L. monocytogenes on intact fruit and vegetable surfaces. Relevant studies were identified by searching seven electronic databases: AGRICOLA, CAB Abstracts, Center for Produce
Safety funded research project final reports, FST Abstracts, Google Scholar, PubMed, and Web of  Science. Searches were conducted using the following terms: Listeria monocytogenes, produce, growth, and survival. Search terms were also modified and “exploded” to find all related subheadings. Included studies had to be prospective, describe methodology (e.g., inoculation
method), outline experimental parameters, and provide quantitative growth and/or survival data. Studies were not included if methods were unclear or inappropriate, or if produce was cut, processed, or otherwise treated. Of 3,459 identified citations, 88 were reviewed in full and 29 studies met the inclusion criteria. Included studies represented 21 commodities, with the majority of studies focusing on melons, leafy greens, berries, or sprouts. Synthesis of the reviewed studies suggests L. monocytogenes growth and survival on intact produce surfaces differ substantially by commodity. Parameters such as temperature and produce  surface characteristics had a considerable effect on L. monocytogenes growth and survival dynamics. This review provides an  inventory of the current data on L. monocytogenes growth and/or survival on intact produce surfaces. Identification of which intact produce commodities support L. monocytogenes growth and/or survival at various conditions observed along the supply chain will assist the industry in managing L. monocytogenes contamination risk.

HIGHLIGHTS

• L. monocytogenes growth and/or survival on intact produce differed by commodity.
• Intact produce held at 208C had the highest L. monocytogenes growth rates.
• Produce surface and storage conditions affected L. monocytogenes growth and/or survival.
• Microbial carrying capacity is crucial to characterizing growth and/or survival patterns.
• Studies need to describe experimental conditions (e.g., relative humidity) for modeling efforts.