Purpose: The study objective was to evaluate lactic acid washes and photohydroionization (PHI) panel, which uses a broad spectrum of wavelengths between ultraviolet light and X-radiation to produce ozone and vapor hydrogen peroxide at low levels, for controlling E. coli O157:H7 on spinach.
Methods: Leaves were dip inoculated in an E. coli O157:H7 cocktail inoculum (5-6 log CFU/ml) for 30 s and then dried for 1 h. Non-inoculated and inoculated leaves were washed for 30 s in food grade lactic acid diluted to 0.5, 1.0, or 2.0% and dried for 10 min. For PHI treatments, leaves were treated for 1, 2, or 5 min per side. Treated leaves were sealed in low-density polyethylene bags prior to enumeration on days 0, 3, 7, 10, and 14. Ten gram samples were diluted and stomached for one min then 0.1 ml was plated onto sorbitol MacConkey agar with cefixime and tellurite plates that were incubated at 37°C for 24 h. Experiment consisted of three replications and two spinach bags per treatment (n = 6).
Results: For lactic acid treatments, there was no difference (P > 0.05) in E. coli O157:H7 populations due to sampling times; pooled times for each lactic acid concentration of 0.5, 1.0, and 2.0% resulted in 2.01, 2.78, and 3.67 log CFU/g reductions. Leaves treated with 1.0 and 2.0% lactic acid had color degradation and were unacceptable by day 14. Escherichia coli O157:H7 populations were reduced 1.6, 1.49, or 1.95 log CFU/g (P> 0.05) for PHI treatments of 1, 2, and 5 min per side.
Significance: All PHI panel contact times and lactic acid wash of 0.5% resulted in > 1.5 and > 2.0 E. coli O157:H7 log reductions on baby spinach and leaves were organoleptically acceptable throughout 14 days shelf life.