Purpose: The objective of this study was to quantify differences in numbers of native microbiota on leafy green produce grown and harvested in south Texas.
Methods: Samples (25.0 g ea.; n = 6) were collected from field-harvested produce from two farms in the Rio Grande valley. Aerobic bacteria, Pseudomonas spp., streptococci, enterococci, coliforms, Escherichia coli, homofermentative and heterofermentative lactic acid bacteria (LAB), yeasts and molds were enumerated on appropriate plating media. Differences between means of log-transformed counts of each microbial grouping from produce commodities by farm were determined by Student’s t-test (P < 0.05).
Results: Pseudomonas spp., homofermentative and heterofermentative LAB mean numbers on lettuce from farm 2 (Temp = 60°F, ERH = 51%) were lower than those on lettuce from farm 1 (Temp = 75°F, ERH = 81%) (P < 0.05). Lettuce from farm 2 bore higher counts of fungi and streptococci versus lettuce from farm 1 (P < 0.05). On spinach, higher counts of aerobic bacteria, pyocyanogenic pseudomonads, yeasts and molds, streptococci, and E. coli were observed from farm 2-obtained samples (Temp = 72°F, ERH = 81%), compared to samples from farm 1 (Temp = 65°F, ERH = 90%) (P < 0.05). Counts of fluorescein-producing pseudomonads, coliforms, and LAB did not differ between these farms (P > 0.05). Parsley from farm 1 (Temp = 76.5°F, ERH = 74%) bore greater numbers (P < 0.05) of homofermentative and heterofermentative LAB versus farm 2 (Temp = 67.5°F, ERH = 48%). No differences between counts of other microbial groupings were observed in parsley (P > 0.05).
Significance: Environmental harvest conditions, including ambient temperature and relative humidity, may have impacted differences in numbers of epiphytic microbiota on leafy greens, which would be expected to affect the efficacy of pre-harvest biocontrol methods using pathogen antagonists. This research suggests need for further analysis of the correlations between harvest conditions and microbiological profile on leafy green produce.