Purpose: The objective of this study was to quantify relative differences in numbers of native microorganisms on skins and rinds versus stem scars of tomatoes and cantaloupes as a function of harvest season.
Methods: Samples were excised from tomatoes and cantaloupes (n = 24) harvested during spring and fall seasons. Skin or rind samples (30 cm2) were pummeled in stomacher bags with 100 ml 0.1% peptone diluent, whereas excised stem scars were placed into sterile vials containing 10 ml peptone diluent and vortexed for 1 min. For both sample types (skin/rind or stem scar), aerobic bacteria, Pseudomonas spp., Streptococcus spp., coliforms, Escherichia coli, heterofermentative lactobacilli, Lactic Acid Bacteria (LAB), and yeasts/molds were enumerated on appropriate microbiological media using standard procedures. Counts from skin or rind were subtracted from counts for the corresponding stem scar from each sample to calculate the log-count difference. For each microbial group, log-count differences were compared by harvest season using analysis of variance (P < 0.05).
Results: Tomato stem scar samples bore greater counts versus skin/rind samples. Mean log-count differences in aerobes were 1.9±0.9 and 0.8±1.4 log10 CFU/cm2 for seasons 1 and 2, respectively (P = 0.039). Likewise, mean log-count differences for yeasts/molds differed across harvest seasons in cantaloupes (0.7±0.5 for season 1 and -0.6±1.4 for season 2; P = 0.008). Significant differences in log-count differences for pseudomonads, heterofermentative lactobacilli, LAB, coliforms, and E. coli were not observed (P > 0.05).
Significance: Numbers of differing members of native microbiota on produce commodities can vary by harvest season, potentially the result of differing climate conditions and harvest practices. Such differences should be considered when developing interventions relying upon interactions of pathogens with native microbiota.