S. R. McKee
Auburn University
Department of Poultry Science,
Auburn, Alabama,
USA
Electron beam irradiation combined with aerobic or vacuum packaging was investigated as a means of extending the shelf-life of skinless, boneless breast fillets stored at 4 C. Boneless, skinless chicken breasts fillets were subjected to an electron beam irradiation dose of 0.8 kGy and stored under aerobic or vacuum packaged conditions for 42 days at 4°C.
Electron beam irradiation completely eliminated coliforms and generic E. coli and the pathogenic organisms, Salmonella and Campylobacter in irradiated breast fillets. Vacuum packaging reduced the amount of lipid oxidation that occurred regardless of irradiation. Non-irradiated fillets had a shelf life of about 14 days whereas the shelf-life of the irradiated fillets was around 42 days at refrigerated storage temperatures.
Introduction
Use of irradiation to improve safety of meat and poultry has been studied for over 40 years, but irradiation has not been favored by consumers because of misconceptions associated with irradiation. However, since FDA approved the use of irradiation in meat and poultry, it is now being reevaluated more as a means for improving safety of these products (Frenzen et al., 2000; Federal Register, 1992). Gamma and electron beam irradiation are the most commonly used irradiation sources for food, but electron beam irradiation is thought to offer several advantages over gamma irradiation (Satin, 1996; Heath et al., 1990). These advantages include higher dose rate capability, accelerators used to generate electron beams can be easily switched on and off, and more importantly, it allows application in a bi-directional manner (top and bottom of product).
Application in a bi-directional is thought to result in more uniform application providing more effective elimination of bacteria on product surfaces. In the US, electron beam irradiation (Surebeam) is being used commercially by several beef companies to ensure safer beef products for consumers. Previous research has shown that electron beam irradiation is effective in reducing microbial contamination in poultry products and extending the shelf-life of poultry (Heath et al. 1990 and Shamsuzzaman et al. 1995). Irradiation treatment has been shown to affect product quality by increasing lipid oxidation and altering color and texture of meat (Shamsuzzanan et al. 1995 and Lewis et al., 2002). Because, the type of irradiation used, the dosage applied, and packaging can effect product quality, it was important to determine the effect of combining low levels of electron beam irradiation with different packaging systems that would potentially retard lipid oxidation and improve product quality.
Therefore, the purpose of this research was to determine the effectiveness of electron beam irradiation at dose of 0.8 kGy in reducing microbial contamination in boneless, skinless chicken breasts.
Material and Methods
Irradiation Treatment
Fresh boneless, skinless chicken breasts that were packaged four fillets per polystyrene tray and shrink-wrapped with polyethylene overwrap were obtained from a commercial processing plant. Breast fillets were randomly divided into groups of no irradiated and irradiated. Vacuum packaging was done using a commercial Multivac system.
At the irradiation facility the next day, a commercial scale electron beam accelerator was used to apply an irradiation dose of 0.8 kGy (10 MeV, 50 kW) in a bi-directional manner. Amount of radiation received was measured by using Far West Technology dosimeters, which were placed in standard dosimeter plates and passed through the irradiation system. Experiments were duplicated with a total of 120 packages of breast fillets being used for microbial analysis and 120 packages used for sensory evaluation.
Microbiological Evaluation
After color determination, the fillets were tested for microbial levels. Total aerobic plate counts and psychrotrophic counts were determined using total aerobic Petri film plates in duplicate. Plates were incubated at 37°C for 48 hours for total aerobic plate microorganisms and 10 d at 4°C for detecting psychrotrophs.
For detection of Salmonella, samples were enriched in tetrathionate broth and plated on the XLT4 agar. Colonies were screened on triple sugar iron agar (TSI) slants and were serologically confirmed with Salmonella O antiserum poly A-I and Vi test kits. For Campylobacter detection, samples were enriched with Bolton broth and buffered peptone water. Defibrinated horse blood was also added to the broth. Samples were incubated in anaerobic gas chambers at 42°C for 32 hours along with atmosphere generating systems (ascorbic acid) and. After 32 hours, the samples were streaked on modified CCDA (MCCDA) plates and incubated at 42°C for 32 hours. Typical colonies were confirmed with a latex agglutination kit specific for Campylobacter.
Sensory Evaluation
Sensory evaluation was conducted biweekly using untrained panelists in the Department of Food Science and Technology. The panelists were served samples from irradiated groups up to day 42 and up to 14 days for controls.
The panelists were served one cooked sample at a time in a pre-determined random order and asked to rate each sample using a modified 9-point Hedonic scale. The Hedonic scale included the attributes of appearance, flavor, and overall acceptability (like extremely to dislike extremely) and texture (extremely moist to extremely dry). Raw product color was determined using a Minolta colorimeter. The degree of oxidative deterioration of the lipids in the fillets was measured using the TBARS analysis method of Witte et al. (1970).
Results and discussion
Electron beam irradiation dose of 0.8 kGy was effective in reducing population levels for total aerobic bacteria and psychrotrophs (Figure 1). As storage time of the breast fillets increased, there was a significant (P <0.05) increase in aerobic and psychotroph population levels for both non-irradiated and irradiated samples. However, the increase in population levels was lower (P <0.05) in irradiated samples. Heath et al. (1990) found that an electron beam irradiation dose as low as 1.0 kGy was effective in reducing total number of aerobic organisms by 2 to 3 logs in whole breasts and thighs.
Results from a study by Luschsinger et al. (1996) indicated that an electron beam dose of 2.5 kGy resulted in a 4-5 log reduction of aerobic plate counts in boneless pork chops.
In the current study, we also determined that 0.8 kGy eliminated Salmonella and Campylobacter (Figure 2). Only the percentage of positive samples will be reported for the current study because MPN was below detection levels for these microorganisms. Heath et al. (1990) showed that an electron beam irradiation dose of 1.0 kGy was also effective in eliminating Salmonella from chicken meat. Lewis et al. (2002) indicated that an electron beam dose of 1.0 kGy was effective in completely eliminating both Salmonella and Campylobacter in chicken breast fillets. Our study indicates the effective level of irradiation to eliminate these pathogens can be reduced even further to 0.8 kGy. Applying an electron beam irradiation dose of 0.8 kGy is an effective means of eliminating bacteria from breast fillets and extending product shelf-life without significantly altering product acceptability.
Specifically, irradiation increased product redness on raw product, but this effect was not detected in cooked fillets (data not shown). Sensory evaluation indicated that electron beam irradiation had no major effects on appearance, texture, flavor, and overall acceptability of the breast fillets (Table 1).
However, as storage time increased, irradiated samples could not be compared to controls be of the high microbial loads present on control samples. Perhaps including a fresh non-irradiated control at each time point would have provided a means for panelists to distinguish quality differences between samples at a given time point. Based on combined microbiological and sensory evaluation results, shelf-life of breast fillets were increased from 14 days to 42 days due to irradiation treatment.
References
Federal Register, 1992. Irradiation of poultry products; Final rule. Food Safety and Inspection Service. Fed. Reg. 57:43588-43600.
Frenzen, P. D., A. Majchrowicz, J. Buzby, and B. Imhoff, 2000. Consumer acceptance of irradiated meat and poultry products. Food Safety Economics, Agriculture Bulletin No. 757.
Heath, J. L., S. L. Owens, and S. Tesch, 1990. Effects of high-energy electron irradiation of chicken meat on Salmonella and aerobic plate count. Poult. Sci. 69:150-156.
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Lewis, S. J., A. Velásquez, S. L. Cuppett, and S. R. McKee, 2002. Effect of electron beam irradiation on poultry meat safety and quality. Poult. Sci. 81:896-903. Satin, M., 1996. Food irradiation. Pages 1-25 in Food Irradiation: A Guidebook. 2nd ed. Technomic Publishing Company, Inc., Lancaster, PA.
Shamsuzzaman, K., L. Lucht, and N. Chuaqui-Offermanns, 1995. Effects of combined electron beam irradiation and sous-vide treatments on microbiological and other qualities of chicken breast meat. J. Food Prot. 58:497-501.
Shea, K. M., 2000. Technical report: Irradiation of Food. Pediatrics. 106:1505-1510. Stone, H. and J. L. Sidel, 1993. Sensory analysis of food. Pages 2-30 in Sensory Evaluation Practices. 2nd ed. Academic, San Diego, CA.
From Proceedings of the "XVI European Symposium on the Quality of Poultry Meat" and the "X European Symposium on the Quality of Eggs and Egg Products", Saint-Brieuc Ploufragan, France.
