This study was conducted to evaluate the effect of biosurfactants on the populations of Escherichia coli
O157:H7 in suspension and on spinach leaves. Eight surfactants including four soybean oil-based biosurfactants,
sodium dodecyl sulfate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), sophorolipid
(SO) and thiamine dilauryl sulfate (TDS) at concentrations of 0.1%, 0.5% and 1.0% were tested in
bacterial suspension, and the most effective biosurfactants were applied on spinach leaves. Results
showed that the soybean oil-based biosurfactants, SDS or Tween 80 did not significantly affect E. coli
O157:H7 populations. SO and TDS at concentrations of 1.0% were effective in reducing E. coli O157:H7
populations in bacterial suspension. E. coli O157:H7 with an initial population of 7.1 log CFU/mL was not
detectable (detection limit: 1 log CFU/mL) after 1 min in 1.0% TDS or after 2 h in 1.0% SO. On spinach
leaves, SO at 1% did not significantly affect E. coli when compared to a water wash during 7 days posttreatment
storage at 4 C. However, TDS (1.0%) wash was as effective as 200 ppm chlorine in reducing
population of spot inoculated E. coli O157:H7, achieving 3.1 and 2.7 log CFU/per leaf at day 0, and 1.4 and
1.9 log CFU/leaf at day 7 when compared with a water wash. No apparent change in spinach visual
quality was observed. None of treatments caused changes in visual quality of spinach. Electron micrographs
suggested ultrastructural damage of bacterial cells such as separation of the outer membrane
from the cytoplasmic membrane. Overall, our results showed that SO and TDS may be potential sanitizers
in inactivating human pathogens such as E. coli O157:H7 in wash water and on fresh produce