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The overall objective of this proposed research effort is to improve food safety by minimizing post-lethality treatment contamination and to extend shelf life of RTE meat and poultry products. Our hypothesis is that a chlorine dioxide gas-sterilized tunnel can effectively be used to aseptically process and package RTE meat products on a pilot scale and eliminate environmental contamination by pathogens. This will be accomplished by developing an aseptic processing and packaging technology in the meat industry under approved regulatory status.<P> Objective one is: to provide fundamental information for optimization of treatment parameters and process design by, determining the efficacy of chlorine dioxide (ClO2) gas for eliminating L. monocytogenes and its biofilm and Pseudomonas biofilm (a potential surrogate for Listeria biofilm) on food-contact surfaces (stainless steel and various plastics for conveyers) as well as L. monocytogenes in the air (i.e. aerosol), and evaluate the effects of ClO2 gas on properties and compatibility with plastic materials commonly used in frankfurter processing. <P> Objective two is to design and develop a pilot scale, continuous tunnel system to aseptically process (cooling and peeling) and package frankfurter products immediately after thermal lethality treatment. The system will be constructed and validated using Pseudomonas biofilm as a surrogate in the pilot plant at Purdue University. <P> Objective three is to integrate the Purdue aseptic processing system with the pilot plant scale processing facilities for frankfurters in a Biosafety Level 2 microbiology laboratory at Iowa State University. Objective 4 is to develop a series of outreach programs for educational and industrial workshops to assist in educating students and transferring the technology to the meat industry, regulatory agencies, and other interested parties.
NON-TECHNICAL SUMMARY: Ready-to-eat (RTE) meat and poultry products are a concern for consumers and meat processors due to risk of contamination with pathogens such as Listeria monocytogenes. Since the products are safe immediately after the commercial cooking process, i.e. smoking in the case of frankfurters, contamination must occur during product peeling, slicing, and packaging. To avoid this potential for product contamination, this project will examine the use of aseptic processing and packaging. This project will explore this technology using frankfurters as a model by: determining the effectiveness of ClO2 gas in eliminating pathogens on equipment surfaces, determining the effect of gas on common equipment materials, i.e. plastics and metals, and constructing a pilot scale, aseptic processing and packaging tunnel for frankfurters. <P>
APPROACH: The aseptic processing system will be designed, constructed and validated at Purdue and further evaluated at ISU by integrating the system with ISU pilot plant. Outreach and extension activities will be carried out from the second year to the end of the project. The first study at Purdue will provide data on the efficacy of ClO2 gas for microbial inactivation on food-contact surfaces used in frankfurter-processing. Treatment parameters (ClO2 conc., exposure time, RH, and temp.) will be varied to establish optimum treatment conditions. L. monocytogenes will be used as target pathogenic microorganisms in the frankfurter processing environment. Pseudomonas biofilm will be studied as a surrogate for L. mono. biofilm during the validation study in objective 2. For air sterilization, L. mono. contaminated aerosol will be prepared in a closed chamber and treated with ClO2 gas. After surface gas treatment, bacteria will be recovered by shaking strips in neutralizing buffer and glass beads followed by plating. The end-point method will also be used to determine the treatment conditions that achieve complete inactivation of the biofilm. Attachment and biofilm structure of target pathogens on stainless steel and plastic surfaces will be investigated using scanning electron microscopy (SEM)and atomic force microscopy (AFM). Viability after ClO2 gas treatment will be visually studied using confocal laser scanning microscopy (CLSM). Materials for the proposed tunnel system including stainless steel and plastic, strips/coupons (2 x 4 cm) of stainless steel (304) and polytetrafluoroethylene (PTFE), will be selected as treatment surface models. Standard ASTM test methods will be used to assess changes in the materials breaking strength, color, tear resistance, and chemical compatibility, etc. after gas treatment as appropriate. In this proposed system design, the tunnel will be used to transfer the cooked products from the cooking operation to the finished packaged products in an aseptic environment. The proposed system will include: ClO2 gas treatment system, buffer chamber/pretreatment, water cooling chamber, peeler chamber, packaging chamber, air filtration, ClO2 recycling, and automation control system. The system will be classified into five zones: thermal treatment oven (smoke house), buffer chamber/pretreatment, cooling, peeling, and packaging. The pretreatment will be located in the buffer chamber so that this system can be applied with both one-door and pass-through smoke houses. The tunnel (15 feet long and 2 feet wide) can be constructed using ClO2 compatible plastic materials (based on the results from Objective 1 study) and 304 stainless steel. After validation of aseptic conditions at Purdue, the tunnel system will be delivered to ISU and further evaluated with different products and L. monocytogenes. Effects of the system on microbial safety (pathogen reduction) and product quality will be determined. Hence, the best treatment conditions will be selected to maximize the quality and safety of products, and minimize operation and equipment cost, environmental effects, etc. <P>
PROGRESS: 2007/09 TO 2008/08 <BR>
OUTPUTS: For the reporting period, progress has been made on objectives 1-3. Under objective 1, the efficacy of chlorine dioxide (CD) gas treatment was determined at 21 deg. C and 75 % relative humidity on a mixture of three strains of Listeria monocytogenes (Scott A, 103M, and N1-227) spot inoculated on surfaces of stainless steel and Teflon (PTFE). The chlorine dioxide gas concentrations ranged from 0.3 mg/l to 2.0 mg/l and exposure times ranged from 2 to 40 minutes. D values for the three strain cocktail ranged from ~ 14 minutes at 0.3 mg/l to 4 minutes at 2 mg/l on stainless steel; and ~ 11 minutes at 0.3 mg/l to 4.2 minutes at 2 mg/l for Teflon surfaces. Similar data was collected on a 4 strain mixture of L. monocytogenes under the same conditions. However, these experimental results showed lower D values (e.g. 2.0 min for stainless steel and 2.8 min for Teflon at 2.0 mg/l) than the 3 strain mixture. Based on the above results, a mixture of four strains of Listeria monocytogenes (Scott A, 103M, N1-227, and 311 for strong biofilm attachment) were spot inoculated (~ 7 log cfu/spot) onto a Hobart meat slicer in different locations including the blade, aluminum base, removable carriage, handles, knobs, etc,. The cells were totally inactivated by chlorine dioxide gas at 2 mg/L after 25 minutes. Experiments were designed for determining the kinetics of Listeria cell inactivation in an aerosol system. A nebulizer (MABISMist II, model 40-270-000) was used to disperse L. innocua (for initial experiments) as aerosol droplets in a CD gas chamber, and the descending aerosol droplets were collected on Petri dishes laid on the bottom of the chamber. This method was similar to one used by Zhang, et al. 2007 in Journal of Food Protection. Vol. 70, No 8, PP 1857-1865. Data indicated that aerosol droplets settled in approximately 120 to 175 minutes. The next step will be to inactivate the cells while they are suspended in air during this time. A method has been developed to grow biofilms of L. monocytogenes (single strains or multiple strains) on stainless steel coupons for up to 4 days. Inactivation results for the biofilms using CD gas indicate that the D values are lower for the biofilm cells than for spot inoculated cells. At 0.3 mg/l (75 % RH and 21 deg. C), the D value for a 24 hr biofilm was only 2.1 min and for a 4 day biofilm only 4.2 min compared to 14 min for the spot inoculated cells. This data is currently being verified and investigated. Results of these experiments were presented at the annual IFT meeting in New Orleans, LA. Under objective 2: Enclosures for a frankfurter peeler and vacuum packager have been designed and are under construction. The current design will be used to demonstrate feasibility of an aseptic chamber for post-thermal-treatment peeling and packaging of frankfurters in a sterile environment. <BR> TARGET AUDIENCES: Food saftey experts <BR> PROJECT MODIFICATIONS: Design of the new tunnel for the frankfurter processing system has been a significant delay. Challenging design considerations have been discussed and the current design will include only manual movement of product through the system for a proof of concept. For example, after a small smokehouse/oven is used to provide the thermal treatment on the frankfurters, the door of the oven will be opened into the sterile zone and the frankfurters will be moved to the peeler, and then to the vaccuum packaging station using various glovebox-type access points. In a commercial system, the additional complexity of a moving conveyor should not have a significant affect on the system sterility.
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IMPACT: 2007/09 TO 2008/08<BR>
The results of experiments on L. monocytogenes cells inoculated onto a commercial meat slicer confirm the log reduction times (D values) of Listeria monocytogenes when treated with chlorine dioxide gas. The results demonstrate that CD gas can be applied to industrial-scale meat processing equipment for completely inactivating Listeria monocytogenes from various surfaces of the equipment. The results of expeiments on L. monocytogenes biofilms indicates that CD (both aqueous and gaseous)may be very effective on biofilms as well.