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Efficacy of Ozone in Killing Listeria monocytogenes on Alfalfa Seeds and Sprouts and Effects on Sensory Quality of Sprouts

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Abstract:

A study was done to determine the efficacy of aqueous ozone treatment in killing Listeria monocytogenes on inoculated alfalfa seeds and sprouts. Reductions in populations of naturally occurring aerobic microorganisms on sprouts and changes in the sensory quality of sprouts were also determined. The treatment (10 or 20 min) of seeds in water (4°C) containing an initial concentration of 21.8 ± 0.1 μg/ml of ozone failed to cause a significant (P ≤ 0.05) reduction in populations of L. monocytogenes. The continuous sparging of seeds with ozonated water (initial ozone concentration of 21.3 ± 0.2 μg/ml) for 20 min significantly reduced the population by 1.48 log10 CFU/g. The treatment (2 min) of inoculated alfalfa sprouts with water containing 5.0 ± 0.5, 9.0 ± 0.5, or 23.2 ± 1.6 μg/ml of ozone resulted in significant (P ≤ 0.05) reductions of 0.78, 0.81, and 0.91 log10 CFU/g, respectively, compared to populations detected on sprouts treated with water. Treatments (2 min) with up to 23.3 ± 1.6 μg/ml of ozone did not significantly (P > 0.05) reduce populations of aerobic naturally occurring microorganisms. The continuous sparging of sprouts with ozonated water for 5 to 20 min caused significant reductions in L. monocytogenes and natural microbiota compared to soaking in water (control) but did not enhance the lethality compared to the sprouts not treated with continuous sparging. The treatment of sprouts with ozonated water (20.0 μg/ml) for 5 or 10 min caused a significant deterioration in the sensory quality during subsequent storage at 4°C for 7 to 11 days. Scanning electron microscopy of uninoculated alfalfa seeds and sprouts showed physical damage, fungal and bacterial growth, and biofilm formation that provide evidence of factors contributing to the difficulty of killing microorganisms by treatment with ozone and other sanitizers.

Keywords:

Document Type: Research Article

Affiliations: 1: Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797 2: Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223- 1797 3: Department of Microbiology, 639 Pleasant Street, Morrill Science Center IV-N203, University of Massachusetts, Amherst, Massachusetts 01003-9298 4: Department of Agricultural and Biological Engineering, Life Sciences Consortium, Pennsylvania State University, University Park, Pennsylvania 16802 5: U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Food Intervention and Technology Research Unit, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA

Publication date: 2003-01-01

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