Progress 09/15/00 to 09/14/05
Outputs
Due to the many health benefits associated with fruit and vegetables, people are eating more raw produce today than ever before. Consumers now demand products that are fresh, of high quality, and safe to eat. During the past two decades, however, more foodborne outbreaks have been associated with consumption of produce. Fruit and vegetable products, such as lettuce, onions, tomatoes, sprouts, berries and fruit juices, have all been associated with contamination and illnesses from organisms including Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, parasites, and viruses. In response to these concerns and consumer demand, alternative microbial reduction strategies are needed. In recent years, the use of antimicrobial gases or vapors has been studied for potential use and application in food manufacturing. Gaseous chlorine dioxide has emerged as a potentially important antimicrobial agent with various applications in food storage and food processing.
Some studies have reported a greater than 5-log reduction for selected pathogens on produce surfaces and food processing equipment surfaces using chlorine dioxide gas. Processing parameters, such as gas concentration, treatment time, relative humidity and temperature all play an important role. In this project, we have developed a batch system and a continuous system that allows us to bring different concentrations of chlorine dioxide gas onto fruit and vegetable surfaces. In these systems, we can also alter temperature, relative humidity and contact time. We have been very successful in optimizing system conditions for pathogen reduction (including Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes) on produce surfaces including green peppers, strawberries, apples, and cantaloupes, each leading to more than a 5-log reduction. Relative humidity and gas concentration are the most important factors for antimicrobial effectiveness. We have also been successful in reducing
pathogens on equipment surfaces including stainless steel, plastic, and epoxy surfaces. We were less effective on meat surfaces and on cut produce. The strong oxidizing agent causes discoloration on these surfaces and leads to a faster onset of rancidity on meats. To better optimize and control system requirements, a pilot plant scale tunnel system is being developed.
Impacts
The use of chlorine dioxide as an alternative antimicrobial treatment for produce could have a significant public health, food quality, and economic impact for the food industry. The new technology, once optimized, will effectively reduce foodborne pathogens which minimizes the risk of foodborne illness. Reduction of spoilage organisms will enhance quality and lengthen product shelf-life.
Publications
- Han, Y., R. H. Linton, and P. E. Nelson 2004. Effects of recovery, plating, and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries. Journal of Food Protection. 67(11) 2436-2442.
- Du, J., Han, Y., and R. H. Linton. 2002. Inactivation by chlorine dioxide gas of Listeria monocytogenes onto different apple surfaces. Food Microbiology. 19:481-490.
- Han, Y., B. Applegate, R. H. Linton, and P. E. Nelson 2003 Decontamination of Bacillus thuringiensis spores on selected surfaces by chlorine dioxide gas. Journal of Environmental Health. 66 (4):16-20.
- Du, J., Y. Han, and R. H. Linton 2003 Efficacy of chlorine dioxide gas in reducing Escherichia coli O157:H7 on apple surfaces. Food Microbiology. 20:583-591.
- Han, Y., T. Selby, K. Schneider, P. E. Nelson, R. H. Linton 2004. Decontamination of strawberries using batch and continuous chlorine dioxide gas treatments. Journal of Food Protection. 67(11) 2450-2455.
- Han, Y. and R. H. Linton 2004. Fate of Escherichia coli O157:H7 and Listeria monocytogenes in strawberry juice and acidified media at different pH values and temperature. Journal of Food Protection. 67(11) 2443-2449.
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Progress 10/01/03 to 09/29/04
Outputs
A pilot scale ClO2 gas treatment system has been developed. This system features automated ClO2 gas generation, concentration, exposure time, and relative humidity control and continuous monitoring, and 30,000 square feet capacity. More than 5 log reductions of selected pathogens (E. coli O157:H7, L. monocytogenes, and Salmonella spp.) were achieved on green peppers, strawberries, mushroom, and oranges after continuous ClO2 gas treatments. Treated products showed insignificant changes in surface color, minimal and acceptable residues (<1mg/kg) of oxidative species, and extended shelf-life. The results strongly demonstrate that ClO2 gas sanitizing treatment is a promising alternative to improve the safety and quality of most fruits and vegetables. The kinetics of aqueous and gaseous ClO2 treatments in inactivating E. coli O157:H7, L. monocytogenes, Bacillus spores, and recombinant bioluminescent E. coli O157:H7 has been studied. The results suggested that moisture
content in the environment surrounding cells plays an important role in microbial inactivation by ClO2 gas. Bioluminescence from the recombinant bacteria could be correlated to microbial survival and may have a potential to on-line monitor the efficacy of ClO2 gas treatment. Mechanism studies indicated that visible damage was not observed on cell membrane instead of interior cell structure after the treatment.
Impacts
Chlorine dioxide gas provides a much greater antimicrobial effect compared to currently used sanitizers and antimicrobial processing systems. The use of chlorine dioxide gas, when conditions are optimized, should provide a far better alternative for treating fruit and vegetable products. In turn, it is expected that produce will be safer and have a longer shelf-life. This provides benefits to the public health sector and economically to the produce industry.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Our objective was to investigate survival and growth of E. coli O157:H7 (EC) and L. monocytogenes (LM) on strawberry surfaces after 7-days at 4C, in strawberry juice, and in acidified media at different pH levels and storage temperatures. Strawberries were spot-inoculated with 8 log cfu/strawberry of each pathogen, dried for 2 hours or stored for 1 or 7 days at 4C, and examined for bacterial survival. Sterile strawberry juice (pH 3.6) and the acidified media containing strawberry juice (pH 3.4-6.8) were inoculated with 6.7 log cfu/ml EC and 7.3 log cfu/ml LM, respectively, incubated at 4 and 37C, and enumerated after 2 hours, 1 or 3 days. Bacteria were recovered using surface plating on sorbital MacConkey agar for EC and modified Oxford agar for LM. Membrane-transferring plating with tryptic soy agar combined with the selective medium was used to recover injured cells. As storage time increased, bacterial populations on strawberries decreased and the level of injured
cells increased. After 7 days storage, a log reduction of 1.0 x 10 2 and 2.7 x 10 3 was observed for EC and LM, respectively. EC survived well at 4C at pH 3.4-6.8, but the percentage of injured cells increased with increasing pH. Injury appeared to be acid-induced and occurred within 2 hours of storage. EC was inactivated at pH less than 3.6 at 37C but could grow at pH 4.7 at 37C. LM was quickly (less than 2 hours) injured at pH less than 4.7 at 4C and inactivated as storage time increased. LM survived well at pH 6.8 at 4C, and grew well at 37C. These results provide information for better recovery and control of selected pathogens in strawberry products. The efficacy of chlorine dioxide (ClO2) gas in inactivating a mixture of Escherichia coli O157:H7 (C7927, EDL933, 204P) on different apple surfaces was investigated. The bacteria were spotted onto the calyx and stem cavities, and the skin at 3, 5, or 8 log cfu/site, air dried, then treated with ClO2 gas at 21oC and 90-95% relative
humidity. Bacterial populations were determined using surface plating, membrane transfer plating, or most probable number method. Bacterial log reductions increased with both increase of ClO2 concentration and treatment time. At least 3-log reductions was achieved after the following ClO2 gas treatments: 12.0 mg/L for 10 min or 3.3 mg/L for 20 or 30 min on the calyx cavities, and 12.0 mg/L for 10 min, 4.8 mg/L for 20 min, or 3.3 mg/L for 30 min on the stem cavities. A 7.2 mg/L treatment for 30 min showed the highest log reduction on the calyx (6.5 +/- 0.7 log) and stem cavities (4.1 +/- .2 log), respectively. More than a 5-log reduction on the skin was achieved by ClO2 gas treatment with 7.2 mg/L for 10 min or 3.3 mg/L for 20 or 30 min. A treatment with 12.0 mg/L for 10 min, 7.2 mg/L for 20 min, or 4.8 mg/L for 30 min completely inactivated the 8-log cfu/site bacteria initially inoculated on the skin, which was determined by an end point method. It was concluded that ClO2 gas
treatment was a promising non-thermal pathogen reduction technique for apples.
Impacts
Chlorine dioxide gas provides a much greater antimicrobial effect compared to currently used sanitizers and antimicrobial processing systems. The use of chlorine dioxide gas, when conditions are optimized, should provide a far better alternative for treating fruit and vegetable products. In turn, it is expected that produce will be safer and have a longer shelf-life. This provides benefits to the public health sector and economically to the produce industry.
Publications
- Du, J., Y. Han, and R. H. Linton 2003. Efficacy of chlorine dioxide gas in reducing Escherichia coli O157:H7 on apple surfaces. Food Microbiology. 20:583-591.
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Progress 10/01/01 to 09/30/02
Outputs
An increase in outbreaks caused by foodborne pathogens has been associated with apple products. Chlorine dioxide gas has been found to be highly effective in reducing pathogens, including Listeria monocytogenes (L. monocytogenes in produce). However, inactivation of L. monocytogenes on apples by chlorine dioxide has not been studied. Our objective was to determine the conditions of chlorine dioxide gas treatments to achieve a 3 or more log reduction of L. monocytogenes on the calyx, stem cavity and pulp surface of apples. Apples were spotted with 5-8 log cfu/spot site of a mixture of L. monocytogenes on the calyx, stem cavities and pulp surfaces. The apples were dried for 2-3 h at 21C in a bio-safety cabinet, and then treated with 1.0- 8.0 mg/L chlorine dioxide gas at 21C and 90% relative humidity. Microbial log reductions were determined using a membrane-transferring-plating method with tryptic soy agar and Modified Oxford agar, a 3-tube MPN method, or an end-point
method. 4.29 and 4.33 log reductions were achieved on the calyx and stem cavities, respectively, by 4.0 mg/L chlorine dioxide gas treatment for 30 min. Using the end point method, an 8.0 mg/L chlorine dioxide treatment for 30 min resulted in complete inactivation of 3.64 to 5.30 log cfu/spotted site on the calyx cavity and a 3.50 - 4.96 log cfu/spotted site on stem cavity. On the pulp surfaces, a 5.52 log cfu/spotted site reduction was observed after a 4.0 mg/L chlorine dioxide treatment for 10 min. Log cfu/spotted site reductions ranging from 3.91 to 6.53 were observed after 4.0 mg/L chlorine dioxide gas treatments for 30 min. Chlorine dioxide gas treatments could achieve more than a 5 log reduction of L. monocytogenes on apple pulp surfaces and more than a 3 log reduction was observed for the calyx and stem areas. Chlorine dioxide gas treatment is a promising non-thermal technique for microbial reduction on apples.
Impacts
Due to the health benefits associated with fruit and vegetables, people are eating more raw produce today than ever before, and at the same time, more foodborne outbreaks have been attributed to raw fruit and vegetable products. In response to these concerns and consumer demand, alternative microbial reduction strategies are needed, especially in food processing operations. Chlorine dioxide gas is a good example of a promising technology that can be used to reduce pathogens in produce. Understanding and developing alternative methods for non-thermal processing will aid in the production of safer and higher quality fruit and vegetable foods.
Publications
- Du, J., Han, Y., and R. H. Linton. 2002. Inactivation by chlorine dioxide gas of Listeria monocytogenes onto different apple surfaces. Food Microbiology. 19:481-490.
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Progress 10/01/00 to 09/30/01
Outputs
Chlorine dioxide (ClO2) has been investigated as a potential non-thermal treatment for inactivation of pathogens in fruit and vegetables. Pathogen contamination in the past decade has been an increasing concern for consumers and the food processing industry. The objective of this project was to evaluate the reduction of Listeria monocytognes on green pepper surfaces after exposure to various ClO2 gas treatments. Reduction of L. monocytogenes Scott A on uninjured and injured surfaces of green peppers after 0.3 and 3 mg/l gaseous and aqueous ClO2 treatment and water washing for 10 min at 20oC was studied. Growth of the L. monocytogenes untreated or treated with 0.6 mg/l ClO2 gas for 30 min at 20oC on green peppers also was investigated. A membrane-surface-plating method was used for resuscitation and enumeration of L. monocytogenes treated with ClO2. The bacterial viability on pepper surfaces was visualized using confocal laser scanning microscopy (CLSM). Live and dead
cells of L. monocytogenes were labeled with a fluorescein isothiocyanate-labeled antibody and propidium iodide, respectively. More than 6 log cfu/5g L. monocytogenes on uninjured surfaces and about 3.5 log cfu/5g on injured surfaces were inactivated by both 3 mg/l and 0.6 mg/l ClO2 gas treatments. The 3 mg/l aqueous ClO2 treatment achieved 3.7 and 0.4 log reductions on uninjured and injured surfaces, respectively; whereas, water washing alone showed 1.4 and 0.4 log reductions, respectively. ClO2 gas treatment was the most effective in reducing L. monocytogenes on both uninjured and injured green pepper surfaces, when compared with aqueous ClO2 treatment and water washing. The significant difference (p < 0.05) between log reductions on uninjured and injured surfaces and the results from CLSM analysis suggested that injured surfaces protected more bacteria from sanitation treatments than did uninjured surfaces. Not only could L. monocytogenes grow on green pepper surfaces at 7oC,
bacteria that survived the 0.6 mg/l ClO2 gas treatment also could grow.
Impacts
The use of ClO2 gas treatments was successful in reducing L. monocytogenes on green pepper surfaces. This new technique may be considered as a new processing alternative for the industry. This technology and model should be further studied for the potential application in food systems.
Publications
- Han, Y., Linton, R. H., Nielsen, S. S., and Nelson, P. E. (2001). Reduction of Listeria monocytogenes on green peppers (Capsicum annuum) by gaseous and aqueous chlorine dioxide and water washing, and its growth at 7oC. J. Food Protection (In press).
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