As an alternative to traditional sanitizers and fumigation agents, gaseous/ vapor-phase antimicrobials certainly have potential for use to improve micro-bial safety and to extend shelf life of fresh and minimally processed fruits and vegetables. Some of the possible applications are presented below.
Technologies could be designed and optimized to treat produce in larger scale operations within a treatment chamber, a storage room, or a continuous belt tunnel using ClO2 or ozone gas that is continuously supplied by generators and monitored throughout the process. The treated produce may be most appropriate in production of fresh-cut products or as ingredients used in juice production. One such application is an automated continuous ClO2 gas treatment system that is being studied and evaluated for decontamination of produce at Purdue University (Figure 18.5). Natural Sterilization &
Fumigation, Inc. (Sparks, NV) has also developed a PureOx ozone gas treatment system for decontamination of fruits and vegetables. Products are treated in a vacuum chamber with controlled ozone generation. McCabe  has also patented a continuous process apparatus and method to treat delicate vegetables, such as potato chips and dehydrated onions, by ozone gas. In this system, products are continuously passed through a treatment zone containing ozone. The products, air, and byproducts (oxygen) of the ozone treatment are separated from the ozone by gravity in a separation zone located above the treatment zone.
Treatments could also be designed and optimized to treat produce in a chamber or a storage room using vapor-phase antimicrobials, such as ClO2. Tsai et al.  evaluated a system for the prevention of potato spoilage during storage using vaporized ClO2. In this system, ClO2 is vaporized by purging air through different concentrations of acidified Oxine (ACD, Bio-Cide International Inc., Norman, OK) solutions, in which ClO2 is the active ingredient. ClO2 vapor is delivered to a treatment chamber or storage facility where the ClO2 treatment is applied to the potatoes based on a calculation dealing with the amount of ClO2 loss in the ACD solution. Using this system with 500 ppm ACD Oxine solution, a 3 to 4 log reduction of Erwinia carotvora and natural flora (aerobic bacteria, yeast, and mold) were found after purging air through the Oxine solution at a flow rate of 6 l/hour for 1 hour.
A closed chamber or package in which ClO2 gas is introduced could also be developed. Using this approach, the gas could be slowly released by sachets, such as sachets that are currently manufactured by ICA TriNova LLC (Figure 18.3). One advantage of this technology is that there is no need for costly and space-consuming ClO2 gas generating systems. Sapers et al.  studied decontamination of apples in a 24.61 high-density polyethylene pail using sachets that generate 0.03 to 0.3 mg/l ClO2 gas in the pail. They found a 3.24 and 4.42log CFU/g reduction of E. coli after treatment with 0.3mg/l ClO2
for 3 hours at 4 and 20°C, respectively, while product quality was minimally affected. After 20 hours' exposure, the microbial reduction approached nearly 5 logs, but darkening of lenticels was also observed. Lee et al.  evaluated the same ClO2 sachets, which slowly released 11, 18, and 26 mg ClO2 gas within 0.5, 1, and 3 hours, respectively, for the decontamination of lettuce in a 20 l chamber. They reported a 4 to 6 log reduction of E. coli, L. monocytogenes, and Salmonella Typhimurium on lettuce leaves.
There may also be an opportunity to treat produce within a plastic film package where the packaging material is designed to allow for a slow and continuous release of the antimicrobial gas or vapor in the package. Bernard Technologies Inc. (BTI, Chicago, IL) has developed two proprietary, controlled-release technologies called Microsphere® and Microlite® that focus on preventing and eliminating biological contamination. Both the Microsphere and Microlite patented sustained release systems  enable the creation of an active Microatmosphere® environment that inhibits the growth of microorganisms and provides an extended shelf life for fruits and/or vegetables. BTI's Microsphere-containing films have been affirmed as a GRAS product by the FDA and U.S. Department of Agriculture (USDA) for use in preserving fresh fruits, vegetables, meat, and poultry products.
The effects of combining antimicrobial vapors or gases with a modified atmosphere packaging strategy to extend the shelf life of fruits and vegetables could also be explored further. Ozen et al.  studied the effects of ozone gas on mechanical, thermal, and barrier properties of several plastic films used in food packaging, including linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), and biaxially oriented nylon (BON) films. Exposure to 2.1 to 4.3 mg/l ozone gas for 2 to 24 hours caused a decrease in tensile strength of OPP, decreased melting temperature of OPP and BON, and reduced oxygen permeability of LLDPE and BON.
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