Summary
Water used for washing or hydrocooling can act as a source of produce contamination with Listeria monocytogenes. Since this could lead to human infections, controlling L. monocytogenes in hydrocooling water and produce is critical for food safety. Commercial disinfectants (chlorine, quaternary ammonium compounds) are not completely effective in killing L. monocytogenes in wash water or on produce, especially in presence of organic load. This proposal aims to investigate the potential of a new technology that employs water containing ultra-fine gas bubbles (size ~ 1 micrometer or less) for washing produce (celery, gala apples, romaine lettuce). We will generate ultra-fine ozone (UFO) bubbles in water using a high energy shear method and test the potential of resulting solution to rapidly kill (in 30 to 60 sec) L. monocytogenes in wash water and on produce surface. In addition, the efficacy of UFO bubble water to synergistically improve the Listeria killing potential of aforementioned commercial disinfectants will be tested. The anti-listerial efficacy of UFO bubble water will also be tested in presence of organic load. Successful completion of this project will provide the produce industry with novel antimicrobial treatment for disinfecting wash water and produce in single pass or re- circulated hydrocooling systems.
Technical Abstract
The widespread distribution of Listeria monocytogenes in agricultural environments such as soil, manure and water results in frequent contamination of food processing areas. Although good agricultural practices partially reduce contamination, however, due to the open nature of farming, it is extremely difficult to completely prevent pathogen influx. Water used for washing or hydrocooling can act as a source of equipment and produce contamination with L. monocytogenes. Since this could lead to human infections, controlling L. monocytogenes in hydrocooling water and on the surface of fresh produce is critical for food safety. Currently used commercial disinfectants (chlorine, peracetic acid, quaternary ammonium compounds) are not completely effective in killing L. monocytogenes in wash water or on the surface of produce, especially in presence of organic load. Moreover, the presence of chemical residues and the formation of harmful organochlorine compounds is an occupational concern due to associated health risks, including cancer. Therefore, there is a need for developing novel strategies that could be employed (either alone or in combination with currently used commercial disinfectants) to control L. monocytogenes in wash water and on surface of fresh produce, vegetables and fruits. This proposal aims to investigate the potential of a new technology that employs water containing ultra-fine gas bubbles (size ~ 1 micrometer or less) for washing produce (celery, gala apples, romaine lettuce). We will generate ultra-fine ozone (UFO) bubbles in water using a high energy shear method and test the potential of resulting solution to rapidly kill (in 30 to 60 sec) L. monocytogenes in wash water and on produce surface. In addition, the efficacy of UFO bubble water to synergistically improve the Listeria killing potential of aforementioned commercial disinfectants will be tested. The anti-listerial efficacy of UFO bubble water will also be tested in presence of organic load. Potential impact from anticipated outcomes: Successful completion of this project will provide the produce industry with novel antimicrobial treatment for disinfecting wash water and produce in dump tanks, and single pass or re-circulated hydrocooling systems. This intervention will translate into increased microbiological safety of fresh produce.
Research Objectives
1. Investigate the stability of ultra-fine ozone (UFO) bubbles in a simulated single pass or circulating hydrocooling system.
2. Investigate the efficacy of UFO bubble water wash (either alone or in combination with commercial sanitizers) in inactivating Listeria monocytogenes on Gala apples, romaine lettuce and celery, and test the survival of the pathogen in the wash water.
3. Evaluate the effect of UFO bubble wash (with or without commercial sanitizers) on shelf life and color of Gala apples, romaine lettuce and celery.
Findings & Recommendations
The overall aim of this proof-of-concept proposal was to investigate the efficacy of a new, nanobubble-based technology in improving the microbiological safety of apples, celery and lettuce. We prepared the antimicrobial solution containing ultra-fine bubbles of ozone, followed by quantification and characterization. The first major finding from this project was that the presence of ozone as ultra-fine bubbles modulates its degradation kinetics in the liquid (Figure 1). This discovery could have major applications in areas where extended contact time is recommended with antimicrobials. Second, we observed that the presence of ultra-fine bubbles of ozone in water was effective in inactivating L. monocytogenes on produce types with different surface texture. For example, washing of apples, celery and lettuce with ultra-fine ozone bubble water significantly reduced the L. monocytogenes load by ~1 log CFU/sample with 1 min of treatment time at 4°C (P<0.05; Figure 3). Ultra-fine ozone bubbles were effective in reducing L. monocytogenes on celery and lettuce at both 25 and 4°C (P<0.05; Figures 2 and 3) without affecting color parameters of the food products (P>0.05; Figure 4).
Based on the findings, ultra-fine ozone bubble water could be used for produce decontamination. Considering that the dissolved ozone concentration used in the experiments was between 5 to 10 ppm, higher concentrations of ozone could be tested for improving antimicrobial efficacy. In addition, combination treatments with currently used disinfectants could also be tested to improve antimicrobial efficacy against L. monocytogenes.