Controlling Listeria monocytogenes on Sliced Ham and Turkey Products Using Benzoate, Propionate, and Sorbate

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1 2306 Journal of Food Protection, Vol. 70, No. 10, 2007, Pages Copyright, International Association for Food Protection Controlling Listeria monocytogenes on Sliced Ham and Turkey Products Using Benzoate, Propionate, and Sorbate KATHLEEN A. GLASS,* LINDSEY M. MCDONNELL, ROB C. RASSEL, AND KRISTINE L. ZIERKE Food Research Institute, University of Wisconsin Madison, 1925 Willow Drive, Madison, Wisconsin 53706, USA MS : Received 12 February 2007/Accepted 30 April 2007 ABSTRACT The objective of this study was to identify concentrations of sorbate, benzoate, and propionate that prevent the growth of Listeria monocytogenes on sliced, cooked, uncured turkey breast and cured ham. Sixteen test formulations plus a control formulation for each product type were manufactured to include potassium sorbate, sodium benzoate, or sodium propionate, used alone and combined (up to 0.3% [wt/wt]), or with sodium lactate sodium diacetate combinations. Products were inoculated with L. monocytogenes (5 log CFU/100-g package) and stored at 4, 7, or 10 C for up to 12 weeks, and triplicate samples per treatment were assayed biweekly by plating on modified Oxford agar. Data showed that 0.1% benzoate, 0.2% propionate, 0.3% sorbate, or a combination of 1.6% lactate with 0.1% diacetate prevented the growth of L. monocytogenes on ham stored at 4 C for 12 weeks, compared with greater than a 1-log increase at 4 weeks for the control ham without antimicrobials. When no nitrite was included in the formulation, 0.2% propionate used alone, a combination of 0.1% propionate with 0.1% sorbate, or a combination of 3.2% lactate with 0.2% diacetate was required to prevent listerial growth on the product stored at 4 C for 12 weeks. Inhibition was less pronounced when formulations were stored at abuse temperatures. When stored at 7 C, select treatments delayed listerial growth for 4 weeks but supported significant growth at 8 weeks. All treatments supported more than a 1-log increase in listerial populations when stored at 10 C for 4 weeks. These results verify that antimycotic agents inhibit the growth of L. monocytogenes on ready-to-eat meats but are more effective when used in combination with nitrite. The U.S. Department of Agriculture Food Safety Inspection Service permits the use of antimicrobial agents to suppress the growth of Listeria monocytogenes on readyto-eat (RTE) meat and poultry products during product shelf life (2, 22). Although many U.S. manufacturers currently utilize lactate and diacetate to prevent the growth of L. monocytogenes in RTE formulations (1), these organic acid salts are less effective in uncured products than in products formulated with nitrite (11, 15, 16, 18). Identifying additional effective antimicrobial ingredients, especially for nitrite-free products, will provide safe and acceptable options for manufacturing without adversely affecting product quality. Three GRAS (generally recognized as safe) additives, sorbate, benzoate, and propionate, are approved for use in a variety of food products other than meats and are acceptable for use on the surface of dry sausages or in pizza crusts to control mold growth (23 25). These antimycotic agents have also been shown to inhibit the growth of several gram-positive bacterial pathogens, such as Clostridium botulinum, Staphylococcus aureus, and L. monocytogenes in media, as well as in and on meat systems (5, 7 9, 13, 14, 17, 21, 26). Preliminary research in our laboratory demonstrated that L. monocytogenes will not grow in wiener or turkey slurries supplemented with 0.25% potassium sorbate, propionic acid, or benzoic acid and stored at 4 or 10 C for up * Author for correspondence. Tel: ; Fax: ; kglass@wisc.edu. to 4 weeks (12). Cured pork-beef bologna that incorporated 0.1% benzoate with propionate, or benzoate with sorbate, into the formulation prevented the growth of L. monocytogenes on bologna stored for 12 weeks at 4 C, compared with a 3.5-log increase in listerial populations in the control bologna without antimicrobials (11). The low concentrations of antimycotic agents were less effective in highmoisture uncured turkey products, but the antimicrobials still slowed listerial growth. When uncured turkey was stored at 4 C for 4 weeks, populations of L. monocytogenes increased 2.5 or 4.5 log CFU per package in the benzoate with propionate or benzoate with sorbate treatments, respectively, compared with a 6.5 log CFU per package increase for the turkey control without antimicrobials. Historically, these antimycotic agents are prohibited in the United States for use within formulations of processed meats if they are used to conceal damage or inferiority or make the product appear to be better or of greater value than it is (9 CFR (25)). However, confirming their efficacy and safety in a variety of products is essential to gain regulatory approval as antilisterial agents and to improve food safety. The objective of this study was to identify concentrations of sorbate, benzoate, and propionate that prevent the growth of L. monocytogenes on sliced, uncured, cooked turkey breast and cured, cooked ham products stored at 4, 7, and 10 C for up to 3 months. MATERIALS AND METHODS Production of RTE turkey and ham. Sixteen test formulations with antimicrobials plus control formulations without an-

2 J. Food Prot., Vol. 70, No. 10 LISTERIA CONTROL IN READY-TO-EAT MEATS 2307 TABLE 1. Initial inoculum and change in populations of L. monocytogenes a on ham b manufactured with various levels of potassium sorbate, sodium benzoate, and sodium propionate c and stored at 4 C for up to 12 weeks Treatment Total % antimycotic Zero time populations (log CFU/pkg) Change in populations (log CFU/package) stored at 4 C at week: Control D d Lactate 1.6% diacetate 0.1% e Propionate 0.05% Sorbate 0.05% Benzoate 0.1% Propionate 0.1% Sorbate 0.1% % Propionate 0.05% 0.05% propionate 0.05% Propionate 0.075% 0.075% Propionate 0.2% Sorbate 0.2% Propionate 0.1% 0.1% Propionate 0.3% Sorbate 0.3% a Data represent mean standard deviation. n 6 for each treatment at each sampling interval, except for control, where n 24. b Ham formulated with 156 ppm of sodium nitrite and 550 ppm of sodium erythorbate on a meat-block basis in compliance with federal regulations. c All percentages are given on a finished weight basis without excessive moisture loss. d D, discontinued because of consistent growth 2 log of L. monocytogenes for two consecutive testing intervals. e Sodium lactate and sodium diacetate were calculated on an anhydrous basis. timicrobials were manufactured for each product type by commercial producers to provide the treatments listed in Tables 1 and 2. Test formulations for each product were chosen to reflect anticipated effective concentrations and to remain within U.S. Food and Drug Administration regulatory limits for other food products. The minimum concentrations of antimicrobials used for the uncured turkey were higher than for cured ham because previous studies demonstrated that the efficacy of antimycotics and lactatediacetate is enhanced in the presence of nitrite (10 12, 18). U.S. regulations limit the total concentration of antimycotic agents to the highest concentration permitted for any one of the ingredients (21 CFR 184.1(d)) (24); thus, when benzoate was included in the formulation, the total of all ingredients did not exceed 0.1%. No upper limits are set for sodium propionate or potassium sorbate for foods that do not meet federal standards of identity, but they must be used in accordance with good manufacturing practices. For this study, treatments that included sorbate or propionate were limited to 0.3% antimycotic agents. Negative growth control for ham was supplemented with 1.6% sodium lactate (calculated on an anhydrous basis) and 0.1% sodium diacetate, whereas uncured turkey was supplemented with 3.2% lactate and 0.2% diacetate to prevent listerial growth. The ingredient statement for control turkey included turkey breast, water, and 2% or less of modified food starch, salt, dextrose, carrageenan, sodium phosphate, and turkey flavor (maltodextrin, salt, and flavor). The ingredient statement for control ham included ham cured with water, salt, and 2% or less of dextrose, sodium phosphate, sodium erythorbate, and sodium nitrite. Uncured turkey breast and cured, smoked composite ham were produced under good manufacturing practices in U.S. Department of Agriculture inspected commercial facilities according to standard industry practices, stuffed into casings, and cooked to the desired endpoint temperature (minimum, 71.1 C [160 F] for ham; minimum, 73.9 C [165 F] for turkey). Cooked, chilled products were sliced on commercial slicers, packaged (vacuum package for turkey; nitrogen flush for ham), and stored at 3 to 4 C through transport to the Food Research Institute, University of Wisconsin Madison, for inoculation and testing. The study was replicated twice. Replicate control treatments were run for each inoculation day. Proximate and chemical analysis. Moisture (5 h, 100 C, vacuum oven method ; (3)), ph (a 10-g homogenized portion diluted 1:10 in distilled water, ph of slurry measured with Accumet Basic ph meter, and Orion 8104 combination electrode, Thermo Fisher Scientific, Waltham, Mass.), NaCl (measured as %

3 2308 GLASS ET AL. J. Food Prot., Vol. 70, No. 10 TABLE 2. Initial inoculum and change in populations of L. monocytogenes a on uncured turkey manufactured with various levels of potassium sorbate, sodium benzoate, and sodium propionate b and stored at 4 C for up to 12 weeks Treatment Total % antimycotic Zero time populations (log CFU/pkg) Change in populations (log CFU/package) stored at 4 C at week: Control D c D Lactate 3.2% diacetate 0.2% d Benzoate 0.1% D D Propionate 0.1% Sorbate 0.1% D D D propionate 0.05% % D D Propionate 0.05% 0.05% Propionate 0.15% Sorbate 0.15% Propionate 0.075% 0.075% Propionate 0.2% Sorbate 0.2% Propionate 0.1% 0.1% Propionate 0.3% Sorbate 0.3% Propionate 0.15% 0.15% a Data represent mean standard deviation. n 6 for each treatment at each sampling interval, except for control, where n 24. b All percentages are given on a finshed weight basis without excessive moisture loss. c D, discontinued because of consistent growth 2 log of L. monocytogenes for two consecutive testing intervals. d Sodium lactate and sodium diacetate calculated on an anhydrous basis. Cl, AgNO 3 potentiometric titration, Brinkman model 682 autotitrator, Metrohm Ltd., Herisau, Switzerland), nitrite (Colorimetric Method (3)), and water activity (Decagon AquaLab CX-2 water activity meter, Decagon, Pullman, Wash.) were assayed by the Food Research Institute for triplicate samples of each formulation; values for protein and fat were provided by the manufacturers. Distribution of sorbate, benzoate, and propionate in the product matrix was determined in treatments with the maximum concentrations of each antimycotic agent and in the lactate-diacetate control. For each trial, two samples taken from different regions of the ham or turkey were assayed by commercial laboratories (gas chromatography method (3)). Concentrations of benzoic acid, sorbic acid, and propionic acid were used to calculate the percentage of potassium sorbate, sodium benzoate, and sodium propionate salts. Preparation of inocula. L. monocytogenes strains Scott A (clinical isolate, serotype 4b), LM 101 (hard salami isolate, serotype 4b), LM 108 (hard salami isolate, serotype 1/2a), LM 310 (goat milk cheese isolate, serotype 4), and V7 (raw milk isolate, serotype 1) were grown individually in 10 ml of Trypticase soy broth (BBL, Becton Dickinson, Sparks, Md.) at 37 C for 18 to 20 h. Cells were harvested by centrifugation (2,500 g, 20 min) and suspended in 4.5 ml of 0.1% buffered peptone water (ph 7.2). Equivalent populations of each isolate were combined to provide a five-strain mixture of L. monocytogenes to yield the target level of 5 log CFU/100-g package. Populations of each strain and the mixture were verified by plating on Trypticase soy agar and modified Oxford agar (Listeria Selective Agar base, Difco, Becton Dickinson, Sparks, Md.). Inoculation and testing. Slices were surface inoculated with L. monocytogenes to provide approximately 5 log CFU per 100-g package (equivalent to 3 log CFU per ml of rinse material). For each package, a total of 0.5 ml of liquid inoculum was distributed over the top surface of each slice, and slices were stacked such that the inoculum was between the slices (4 slices for turkey; 10 slices for ham). Inoculated products were vacuum packaged (Multivac AGW, Sepp Haggemuller KG, Wolfertschewenden, Germany) in gas-impermeable pouches (3 mil high barrier ethylene vinyl alcohol copolymer pouches, Deli 1 material; oxygen transmission, 2.3 cm 3 /cm 2 ;24hat24 C; water transmission, 7.8 g/cm 2 ;24h at 37.8 C; and 90% relative humidity; WinPak, Winnepeg, Manitoba, Canada) and stored at 4, 7, and 10 C for up to 12 weeks. Triplicate inoculated samples for each treatment were assayed for changes in L. monocytogenes populations, and duplicate un-

4 J. Food Prot., Vol. 70, No. 10 LISTERIA CONTROL IN READY-TO-EAT MEATS 2309 TABLE 3. Proximate analysis of turkey and ham a Turkey Ham Moisture (%) (range, ) (range, ) NaCl (%) (range, ) (range, ) ph Water activity Nitrite (ppm) Not added Protein (%) b Fat (%) a Results are an average standard deviation for analysis of six samples for each of the 16 formulations (n 96). b Protein and fat levels reported by manufacturer. inoculated samples were assayed for changes in lactic acid bacteria and ph at zero time; at 2, 4, 6, 8, 10, and 12 weeks storage at 4 C; and at 4, 8, and 12 weeks only at 7 and 10 C. In addition, changes in odor and turbidity in the package exudate were noted for all samples. Bacterial populations were determined in rinse material obtained after adding 100 ml of sterile Butterfield phosphate buffer to each package and massaging the contents externally by hand for about 3 min. L. monocytogenes was enumerated by surface plating serial (1:10) dilutions of rinse material on modified Oxford agar. Select colonies were confirmed as L. monocytogenes by Gram staining, tumbling motility, CAMP test, hemolysis on Trypticase soy agar with sheep blood, and biochemical analysis with MICRO-ID Listeria (Remel, Lenexa, Kans.). Testing of a treatment was discontinued if listerial growth (a 2-log increase) was confirmed for packages tested for two consecutive sampling intervals. To determine the effect of the experimental treatments on the growth of spoilage microorganisms that might ultimately affect the growth of L. monocytogenes, changes in ph and populations of competitive microflora were evaluated. Only uninoculated samples were assayed, because the total microbial counts for the inoculated samples would have primarily recovered populations of the inoculated and growing L. monocytogenes and would not have given any indication of the growth of indigenous spoilage microorganisms on the products. The ph was measured by removing representative 10-g uninoculated samples prior to rinsing and homogenizing them with 90 ml of hot deionized water with a lab blender (Stomacher 400, A.J. Seward, London, UK). The homogenized sample was allowed to cool to room temperature, any fat was removed from the surface, and the ph was measured on the slurry. Populations of lactic acid producing bacteria were assayed for the remaining portion of the uninoculated samples by plating rinse material on All Purpose Tween agar (Difco, Becton Dickinson) with 0.002% bromcresol purple (25 C, 48 to 72 h). Statistical analysis. The microbiological data reported are average values and standard deviations for triplicate samples and two separate trials for each test formulation (n 6) and eight replications for each positive control formulation (n 24). Differences between the experimental treatments and the positive control were analyzed by the General Linear Models procedure with Fisher s least significant difference test at each sampling interval (SAS 9.1.3, SAS Institute, Cary, N.C.). All statistically significant differences reported were at the P 0.05 level. RESULTS AND DISCUSSION Proximate analyses. Proximate analyses demonstrated variability similar to what could be expected in typical TABLE 4. Analysis of antimycotic agents for select formulations a Formulation (target antimicrobial level) % sodium benzoate % potassium sorbate % sodium propionate Ham 0.1% sodium benzoate % potassium sorbate % sodium propionate Lactate-diacetate control; no antimycotic Turkey 0.1% sodium benzoate % potassium sorbate % sodium propionate a Gas chromatography method (3), measured as an acid form and converted to a percent basis of salt form. Benzoate and sorbate analyzed by R-Tech Laboratories, Arden Hills, Minn.; propionate analyzed by Covance Laboratories, Madison, Wis. Average for four samples standard deviation. commercial production (Table 3). Average moisture (75.04% 1.08%) and ph ( ) values for turkey were slightly greater than for ham (73.65% 0.27% moisture and ph ), and salt values were lower in turkey (1.71% 0.20%) than in ham (2.59% 0.02%). Average residual nitrite recovered from ham was ppm; nitrite was not analyzed for the uncured turkey treatments. No correlation was found between microbial growth and analytical values for treatments within a given product type (data not shown). Concentrations of benzoate and sorbate were within expected target range for both the turkey and ham products. Analyzed values were consistent between samples taken from different regions of a package or between samples from the duplicate trials (Table 4). In contrast, propionate concentrations reported by a commercial laboratory that used the gas chromatography method were 0.1 and 0.006% propionate for the turkey and ham, respectively. These results were significantly lower than the target 0.3% propionate for each product. Given the consistent inhibition of L. monocytogenes in the treatments formulated with 0.3% propionate, reported results are either due to the commercial laboratory error or the decomposition of propionic acid during processing or frozen storage. No remaining uninoculated samples were available for retesting to confirm the discrepancy. Consumer taste preference panels for freshly prepared ham and turkey were completed at the University of Wisconsin Madison campus (6). For both product types, consumer preference was compared (pairwise comparison) with the control without antimicrobials, with 0.3% sorbate, and with 0.3% propionate. In addition, ham treatments con-

5 2310 GLASS ET AL. J. Food Prot., Vol. 70, No. 10 taining 0.1% benzoate and 1.6% lactate plus 0.1% diacetate were evaluated. Consumers preferred the flavor of ham with 0.3% propionate or 0.1% benzoate over the lactate-diacetate treatment, and there was no significant difference with regard to the control ham without antimicrobials added. The addition of 0.3% sorbate rated lowest in consumer preference. Consumers rated deli-style turkey containing sorbate equivalent to control turkey without antimicrobials. In contrast, consumers did not prefer the turkey containing propionate over the control turkey. However, when a direct comparison of sorbate was made to propionate, no preference was noted. Control of L. monocytogenes. Results from this study demonstrated that antimycotic agents significantly inhibit the growth of L. monocytogenes when incorporated into the formulations of RTE cured ham and uncured turkey products compared with the control without antimicrobials. L. monocytogenes growth was significantly inhibited (P 0.05) in ham stored at 4 C for 12 weeks when the product was formulated with 0.1% benzoate, 0.2% propionate, 0.3% propionate, 0.3% sorbate, combined 0.1% propionate with 0.1% sorbate, or 1.6% lactate with 0.1% diacetate (Table 1). Other treatments, including those supplemented with 0.1% combined benzoate, propionate, or sorbate, 0.1% propionate, 0.1% sorbate, or 0.2% sorbate, delayed growth 6 to 10 weeks at 4 C but supported more than 1 log growth in sporadic samples prior to 12 weeks. The control treatment without antimicrobials and treatments with only 0.05% of any individual antimycotic agents supported 0.6 to 1.1 log growth when stored at 4 C for 2 weeks. Antimicrobial treatments were less effective when the ham was stored at temperatures greater than 4 C. Ham containing 0.1% sorbate with 0.1% propionate, 0.2% propionate, 0.2% sorbate, or 1.6% lactate with 0.1% diacetate delayed listerial growth for 4 weeks at 7 C, but all formulations supported more than a 1-log increase at 8 weeks (data not shown). For products stored at 10 C, only 0.3% propionate delayed pathogen growth for 4 weeks (an average 1-log increase), whereas all the other treatments supported a 2- to 4-log increase during the same interval (data not shown). Antimycotic treatments significantly inhibited (P 0.05) L. monocytogenes growth in uncured products, but higher concentrations of each antimicrobial were required. Uncured turkey supplemented with 0.2% propionate, combinations of 0.1% propionate with 0.1% sorbate, or 3.2% lactate with 0.2% diacetate significantly inhibited L. monocytogenes growth (less than a 1-log increase) when stored at 4 C for 12 weeks (Table 2). A combination of 0.075% propionate with 0.075% sorbate prevented pathogen growth in samples from only one replicate trial for the duration of the study. Turkey with 0.3% sorbate unexpectedly supported a 1-log increase for both trials when stored for 8 weeks at 4 C, whereas 0.2% sorbate delayed growth for 10 weeks. Chemical analysis of the turkey with 0.3% sorbate did not suggest insufficient addition or uneven distribution of sorbate within the product matrix. As described below, low concentrations of competitive spoilage microflora were typically recovered from the treatments, and sporadic growth did not correlate with the inhibition of L. monocytogenes. Therefore, the growth of competitive microflora was unlikely the cause of the delay of listerial growth for the 0.2% sorbate turkey treatment. Additional study is required to define factors that affect the use of 0.3% sorbate as an antilisterial agent in high-moisture, uncured products. As observed for the ham treatments, inhibition was less pronounced when turkey formulations were stored at abuse temperatures. Treatments, including 0.15% sorbate with 0.15% propionate, 0.2% propionate, 0.3% propionate, and 1.6% lactate with 0.1% diacetate, delayed listerial growth for 4 weeks (less than a 1-log increase) when stored at 7 C but supported significant growth (a 2-log increase) at 8 weeks. None of the treatments delayed listerial growth when stored at 10 C; populations of L. monocytogenes increased by 1.5 to 5.5 log in all formulations stored at 10 C for 4 weeks (data not shown). Other researchers have similarly reported less antimicrobial activity against L. monocytogenes when treated substrate is stored at abuse temperatures. Control of spoilage. The growth of spoilage lactic acid bacteria and changes in ph were inconsistent among samples within any given treatment. Although most sample populations were under the detectable limit with direct plating (less than a 1-log CFU/ml rinse), populations for some samples increased 5 to 8 log CFU throughout the study (data not shown). Similarly, the ph of the uninoculated samples tested did not decrease appreciably for most samples. Less than a 0.15 ph unit decrease was observed throughout the testing interval for most samples, regardless of the growth of spoilage microflora. Several samples that were grossly spoiled (turbid purge, offensive off-odor, or both) demonstrated a 0.7 to 1.4 ph unit decrease, whereas the ph of other grossly spoiled samples decreased only 0.2 to 0.4 unit. There was no evidence that the antimycotic treatments would inhibit spoilage microflora and mask spoilage compared with the controls. This study demonstrates that antimycotic agents inhibit the growth of L. monocytogenes when incorporated into formulations of RTE meats and that they are more effective in high salt products with nitrite than in low-salt, uncured products. Of the three antimycotic agents used in this study, sorbate had the least inhibitory effect on L. monocytogenes growth on a percent basis. When calculated on a molar basis, 0.1% (wt/wt) is equivalent to 0.07, 0.07, and 0.1 M for the potassium sorbate, sodium benzoate, and sodium propionate, respectively. Several factors may contribute to the efficacy of each antimycotic agent in this study, but the exact mechanism is unknown. Given the ph values for the RTE products assayed in this study and the dissociation constants for sorbic, propionic, and benzoic acids (pk a 4.8, 4.87, and 4.2, respectively), the proportion of undissociated acid in the substrate is small. For example, at ph 6.25, only 3.07 and 0.88% of sorbic and benzoic acid, respectively, are in the undissociated acid form capable of diffusing across the

6 J. Food Prot., Vol. 70, No. 10 LISTERIA CONTROL IN READY-TO-EAT MEATS 2311 plasma membrane and disrupting intracellular ph and cellular function (20). Other researchers suggest that sorbate and benzoate inhibit bacterial growth by altering membrane structure, by changing membrane proteins, or by altering membrane fluidity (19). Buazzi and Marth (4) proposed that high concentrations of sodium propionate damage L. monocytogenes at neutral ph by inhibiting the synthesis or activity of lactic dehydrogenase or by affecting the availability of cations in the cell. Although the experimental design of this study did not specifically include moisture and ph as variables, these factors can also have a significant effect on the efficacy of antimicrobials. Previous research has shown that combinations of 0.05% benzoate with 0.05% sorbate or 0.05% benzoate with 0.05% propionate prevented the growth of L. monocytogenes on cured pork-beef bologna with approximately 57% moisture and ph 6.1 (11). This study demonstrated that the same concentrations of antimycotic agents were significantly less inhibitory in cured ham products that contained approximately 74% moisture and ph 6.3. Similar trends have been observed for cured meat products formulated with lactate-diacetate combinations. For example, a combination of 0.1% diacetate, 1.6% lactate, and 2.5% NaCl is predicted to suppress the growth of L. monocytogenes for 77 days on 75% moisture, cured products, but the same combination would delay growth for more than 360 days if comparable products were formulated with 57% moisture (OptiForm Listeria Growth Suppression Model, Purac North America, Lincolnshire, Ill.). This research verifies that propionate, benzoate, and sorbate will enhance the safety of high-moisture RTE cured and uncured meat and poultry products when used at concentrations that are deemed safe and acceptable for other food products. Additional research should be completed to validate the specific concentrations of propionate, benzoate, or sorbate required to control L. monocytogenes in other formulations of RTE products. ACKNOWLEDGMENTS Thank you to Scott Wyman, Nicole Hardy, and Garret Kau for technical assistance in completing laboratory work. We greatly appreciate the generous donations of test product by Sara Lee Foods and Land O Frost and helpful discussions with Dr. James Claus, Meat and Animal Science, University of Wisconsin Madison; Dr. Wafa Birbari, Sara Lee Foods; Mr. John Butts, Land O Frost; and Dr. Andy Milkowski, Kraft-Oscar Mayer (retired). This study was funded by the American Meat Institute Foundation and by contributions from the food industry. REFERENCES 1. 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7 2312 GLASS ET AL. J. Food Prot., Vol. 70, No. 10 ognized as safe. Code of Federal Regulations, Title 21, Part 182. Office of the Federal Register, U.S. Government Printing Office, Washington, D.C. 24. U.S. Food and Drug Administration Direct food substances affirmed as generally recognized as safe. Code of Federal Regulations, Title 21, Part 184. Office of the Federal Register, U.S. Government Printing Office, Washington, D.C. 25. U.S. Department of Agriculture Food Safety and Inspection Service Food ingredients and sources of radiation. Code of Federal Regulations, Title 9, Part 424, Subpart C. Office of the Federal Register, U.S. Government Printing Office, Washington, D.C. 26. Wederquist, H. J., J. N. Sofos, and G. R. Schmidt Listeria monocytogenes inhibition in refrigerated vacuum packaged turkey bologna by chemical additives. J. Food Sci. 59: , 516.