Inactivation of bacterial pathogens on lettuce, sprouts, and spinach using hurdle technology

초록

Effects of chemical treatment using slightly acidic electrolyzed water (SAEW), fumaric acid (FA), or calcium oxide (CaO) and physical treatment using ultrasonication (US), micro-bubbles (MB), or ultraviolet (UV) to inactivate bacterial pathogens Listeria monocytogenes, Escherichia call 0157:H7, Staphylococcus aureus, and Salmonella spp. on lettuce, spinach, and sprouts were determined. Fresh produce inoculated with bacterial pathogens (similar to 9 log CFU/mL) was immersed in distilled water (DW), SAEW, FA (0.5%), or CaO (0.2%) alone or in combination at 23 +/- 2 degrees C for 3 min followed by treatment with US, MB for 3 min, or UV for 10 min. Effects of combined treatment on shelf-life of lettuce at 4 degrees C and 23 +/- 2 degrees C were also determined in this study. Results revealed that the use of a combination of CaO + SAEW + FA + US exhibited significant reduction (p < 0.05) for bacterial pathogen on fresh produce compared to individual treatment or other combinations. CaO + SAEW + FA + US treatment exhibited highest reduction of E. coli 0157:H7, S. aureus, L. monocytogenes and Salmonella spp. by 4.7, 4.9, 4.84 and 5.08 log CFU/g, respectively on lettuce as compared to spinach and sprouts. Microbial count reducing capability for combined treatment methods were ranked in the following order: SAEW + FA < CaO + SAEW + FA < CaO + SAEW + FA + US. However, introduction of US to CaO + SAEW + FA treatment resulted in little detrimental effect on the overall quality of lettuce. Moreover, CaO + SAEW + FA treatment effectively enhanced the shelf-life of lettuce stored at 4 degrees C and 23 +/- 2 degrees C by about 6 days and 3 days, respectively as compared to control (DW treatment), with longer lag time (23.11 h on lettuce) for naturally occurring bacteria on fresh produce. These findings suggest that significant synergistic benefit could be obtained from combined sanitizer treatment to eliminate bacterial pathogens from fresh produce.

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