Bacterial Contamination and Microflora of Several Fresh Produce

Viable counts were enumerated in 36 raw samples of 19 different vegetables. Coliform, fecal coliform, and E. coli were determined in 31 vegetable samples. Tomato was found to have the lowest viable count of 2.12 log cfu/g while radish sprout had the highest count of 9.05 log cfu/g. Although E. coli was not detected in all the vegetables tested, most of these vegetables were positive for fecal coliform. Viable counts of the tenth leaves from the outside were lower by only 1 log cfu/g than that of the outermost leaves in cabbage and lettuce. Among viable counts of vegetable parts, celery leaves, lower stems in radish sprout, and spinach were found to have the highest viable counts of 7.28 log cfu/g, 9.27 log cfu/g, and 6.10 log cfu/g respectively while lower stem in parsley had the lowest count of 5.10 log cfu/g. The microflora of the four vegetables, celery, parsley, radish, and radish sprout were determined by using biochemical methods. There were 105, 50, 48, 130, and 61 bacterial isolates from celery, lettuce, parsley, radish, and radish sprout, respectively. The predominant bacterium on the four vegetables was about 30-60% Gram-negative Flavobacterium or Xanthomonas. Other Gram-negative bacteria isolated from the vegetables include 11% Neisseria or Veillnella (celery), 18% Moraxella (radish), 15% Alcaligenes and 12% Pseudomonas (radish sprout) while Enterobacteriaceae accounted for less than 5% for each of the flora of celery, parsley, and radish sprout. On the contrary, parsley had 25% Kurthia or Bacillus, and 13% Micrococcus, both Gram-positive

Comparison of the Bactericidal Effect of Slightly Acidic Hypochlorous Water with That of Conventional Sterilizers

The bactericidal effect of slightly acidic hypochlorous water (SAHW) on Salmonella Enteritidis, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus, as well as some bacterial strains isolated from fresh lettuce was evaluated. Viable counts of all tested bacterial samples decreased immediately after treatment by SAHW. Most bacterial cells with the exception of B. cereus, and S. aureus were not culturable on TSA after treatment by 1 to 30 mg/L SAHW. Likewise, Pseudomonas sp., and Flavobacterium or Xanthomonas sp., Kurthia sp., Micrococcus sp., and Corynebacterium or Microbacterium sp. were not culturable on TSA after treatment by 30 mg/L SAHW. Viable counts of S. aureus, E. coli, Flavobacterium or Xanthomonas sp., and Pseudomonas sp. showed a 5 to 6 log cfu/mL reduction at day 0 and maintained a count of less than 1 log cfu/mL from day 1 to day 7 following treatment by 30 mg/L SAHW. Sodium hypochlorite (NaOCl, 0.5-1.0 mg/L) decreased the viable counts of S. Enteritidis　to less than the lower limit of detection, 1 log cfu/mL, from day 1 to day 7 following treatment by 1 mg/L. NaOCl was not sufficient at 0.5-0.75 mg/L in reducing viable counts of S. Enteritidis because of a 2 to 5 log cfu/mL increase from day 2 to day 5 due to recovery from injury. Initial counts of S. Enteritidis after hydrogen peroxide (H2O2, 1000-2000 mg/L) treatment slowly decreased over time to less than 1 log cfu/mL after day 2. Treatment by 1750 to 2000 mg/L H2O2 has sufficient bactericidal activity on S. Enteritidis cells, however, at a higher concentration compared to NaOCl or SAHW. SAHW decreased viability of S. Enteritidis immediately with higher reduction counts in 1, 5, and 30 mg/L from day 0 to day 7 unlike NaOCl and H2O2