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

Ngnitcho, Paul-François Kounkeu, Khan, Imran, Tango, Charles Nkufi, Hussain, Mohammad Shakhawat, Oh, Deog Hwan
Innovative food science & emerging technologies 2017 v.43 pp. 68-76
Escherichia coli O157, Listeria monocytogenes, Salmonella, Staphylococcus aureus, acidity, bacteria, calcium oxide, chemical treatment, electrolyzed water, fresh produce, fumaric acid, lettuce, microbubbles, pathogens, sanitizers, shelf life, spinach, ultrasonic treatment
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 coli O157:H7, Staphylococcus aureus, and Salmonella spp. on lettuce, spinach, and sprouts were determined. Fresh produce inoculated with bacterial pathogens (~9logCFU/mL) was immersed in distilled water (DW), SAEW, FA (0.5%), or CaO (0.2%) alone or in combination at 23±2°C for 3min followed by treatment with US, MB for 3min, or UV for 10min. Effects of combined treatment on shelf-life of lettuce at 4°C and 23±2°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 O157:H7, S. aureus, L. monocytogenes and Salmonella spp. by 4.7, 4.9, 4.84 and 5.08logCFU/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°C and 23±2°C by about 6days and 3days, respectively as compared to control (DW treatment), with longer lag time (23.11h 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.