Control of Salmonella enterica Typhimurium in chicken breast meat by irradiation combined with modified atmosphere packaging.

Salmonella is one of the leading causes of human foodborne illnesses originating from meat and poultry products. Cross-contamination of Salmonella from raw to cooked products continues to be problematic in the food industry. Therefore, new intervention strategies are needed for meat and poultry products. Vacuum or modified atmosphere packaging (MAP) are common packaging techniques used to extend the shelf life of meat products. Irradiation has been well established as an antibacterial treatment to reduce pathogens on meat and poultry. Combining irradiation with high-CO(2)+CO MAP was investigated in this study for improving the control of Salmonella enterica Typhimurium on chicken breast meat. The radiation sensitivities (D10-values) of this pathogen in chicken breast meat were found to be similar in vacuum and in high-CO(2)+CO MAP (0.55 ± 0.03 kGy and 0.54 ± 0.03 kGy, respectively). Irradiation at 1.5 kGy reduced the Salmonella population by an average of 3 log. Some Salmonella cells survived in both vacuum and high-CO(2) + CO MAP through 6 weeks of refrigerated storage following irradiation. This pathogen also grew in both vacuum and MAP when the product was held at 25°C. This study demonstrated that irradiation is an effective means of reducing Salmonella on meat or poultry, but packaging in either vacuum or MAP had little impact during subsequent refrigerated storage.

Influence of nisin and selected meat additives on the antimicrobial effect of ovotransferrin against Listeria monocytogenes.

The objective of this study was to determine the effect of nisin and selected meat additives (salt, lactate, lactate-diacetate combination, and polyphosphate) on the antimicrobial activities of ovotransferrin (OTF) against the growth of Listeria monocytogenes. A Bioscreen C turbidometer (Oy Growth Curves AB Ltd., Helsinki, Finland) was used to evaluate the effect of various concentrations of nisin and individual meat additives on the antilisterial activity of OTF in brain heart infusion (BHI) broth. The concentrations of OTF, meat additives, nisin, and their combinations that proved most inhibitory to L. monocytogenes were selected and their antilisterial effects were tested using frankfurters. Frankfurters were inoculated with L. monocytogenes (~6.0 log(10) cfu/frankfurter); treated with OTF, meat additives, and nisin singly or in combination; and held under vacuum at 4, 10, or 25°C. At 40 mg/mL, OTF strongly suppressed (3.46 log at 4 h and 2.59 log at 12 h) the growth of L. monocytogenes in BHI broth compared with the control. A combination of OTF (40 mg/mL) and nisin (1,000 IU) inhibited the growth of L. monocytogenes in BHI and in frankfurters held at 25°C below the detection limit (1 cfu/mL) at 12 h. However, the antimicrobial effect of OTF (40 mg/mL) alone was not observed in frankfurters at all temperatures used in this study. Nisin (1,000 IU), OTF (40 mg/mL), and nisin (1,000 IU) combination completely inhibited the growth of L. monocytogenes in frankfurters at all temperatures during 3 d. Salt at 0.5 and 1%, lactate at 0.78 and 1.56%, and lactate (1.56%) + diacetate (0.01%) did not alter the inhibitory effect of OTF against the pathogen in BHI, but salt at 2% or polyphosphate at 0.05% negated the growth inhibitory effect of OTF against L. monocytogenes. This study demonstrated that combination of OTF and nisin was effective in controlling L. monocytogenes.

Influence of zinc, sodium bicarbonate, and citric acid on the antibacterial activity of ovotransferrin against Escherichia coli O157:H7 and Listeria monocytogenes in model systems and ham.

The influence of NaHCO(3) and citric acid on the antibacterial activity of apo-ovotransferrin in model systems and ham was investigated. The antibacterial activity of 20 mg/mL of ovotransferrin solution with added NaHCO(3) (0, 25, 50, or 100 mM) or citric acid (0.25 or 0.5%) was evaluated against Escherichia coli O157:H7 and Listeria monocytogenes in brain heart infusion broth. The antimicrobial activity of ovotransferrin saturated with Fe(2+) or Zn(2+) against both pathogens was also measured. In addition, ovotransferrin solutions containing either 100 mM NaHCO(3) or 0.5% citric acid were applied to commercial hams inoculated with E. coli O157:H7 or L. monocytogenes and stored at 4 degrees C for 4 wk. The antimicrobial activity of ovotransferrin increased as the concentration of added NaHCO(3) increased. Sodium bicarbonate (100 mM) significantly improved the antibacterial activity of ovotransferrin against E. coli O157:H7 and L. monocytogenes. Citric acid (0.5%) combined with ovotransferrin resulted in a synergistic antibacterial effect against E. coli O157:H7, and L. monocytogenes was susceptible to 0.5% citric acid alone. Sodium bicarbonate diminished the strong antibacterial activity of ovotransferrin + citric acid against E. coli O157:H7, and use of sodium citrate instead of citric acid did not produce any antibacterial activity against the pathogens. The antimicrobial activity of ovotransferrin increased significantly under acidic conditions. The Zn-bound ovotransferrin prevented the growth of L. monocytogenes as detected in the apo-ovotransferrin combined with 100 mM NaHCO(3) treatment, but Fe-bound ovotransferrin had little or no inhibitory activity against E. coli O157:H7 and L. monocytogenes. Ovotransferrin + 100 mM NaHCO(3) did not exhibit any antibacterial activity against the 2 pathogens in commercial hams, whereas ovotransferrin + 0.5% citric acid suppressed the growth of L. monocytogenes in irradiated hams. In conclusion, combinations of ovotransferrin with NaHCO(3), citric acid, or Zn(2+) enhanced the antibacterial activity of ovotransferrin against E. coli and L. monocytogenes, but there are some limitations as discussed for applying ovotransferrin to meat or meat products.

Effect of ethylenediaminetetraacetate and lysozyme on the antimicrobial activity of ovotransferrin against Listeria monocytogenes.

This study evaluated the effect of EDTA and lysozyme on the antibacterial activities of activated ovotransferrin against 5 strains of Listeria monocytogenes. First, a disc test was performed to screen the concentrations of EDTA or lysozyme that showed antibacterial activities in ovotransferrin (O) or ovotransferrin in 100 mM NaHCO3 (OS) solution. Turbidity and viability tests were conducted using O or OS solution combined with either lysozyme (OL and OSL) or EDTA (OE and OSE). Also, OS combined with 2 mg/mL of lysozyme (OSL) or 1 mg/mL of EDTA (OSLE), or both, was applied on commercial hams to determine if the solutions show antibacterial activities on meat products. The effect of initial cell population on the antibacterial activities of ovotransferrin combined with either EDTA or lysozyme was also determined. The L. monocytogenes started to grow after 1 d of incubation in the presence of >2.0 mg/mL of lysozyme. The OL groups showed weak antibacterial activities against L. monocytogenes in brain heart infusion broth culture, and their activities were bacteriostatic. The OSL groups were bactericidal against L. monocytogenes, resulting in 1 log reduction from initial cell population. Even though OSL showed stronger antibacterial activity than OS, lysozyme had no significant effect on antibacterial activity of OS against L. monocytogenes. Also, EDTA itself at 1.0 and 2.0 mg/mL was bacteriostatic against 5 strains of L. monocytogenes. They were more susceptible to EDTA than lysozyme, and OSE1 and OSE2 had bactericidal activity against L. monocytogenes. There was a significant difference in the survivor cell populations between OS and OSE groups (P < 0.05). Therefore, EDTA enhanced the antibacterial activity of OS against L. monocytogenes. However, ovotransferrin plus either lysozyme or EDTA, or both, did not show any antibacterial effect in commercial hams during storage at 10 degrees C. In addition, the initial population of L. monocytogenes cells influenced the antibacterial activity of OSL or OSE.

Influence of four retail food service cooling methods on the behavior of Clostridium perfringens ATCC 10388 in turkey roasts following heating to an internal temperature of 74 degrees C.

The influence of four food service cooling methods (CM) on growth of Clostridium perfringens ATCC 10388 in cooked turkey roasts was evaluated. Raw whole turkey roasts were inoculated with C. perfringens spores (approximately 4.23 log CFU per roast), vacuum packaged, and heated to an internal temperature of 74 degrees C. The cooked roasts were cooled as follows: whole roast cut into four quarters and held at 4 degrees C (CM1); whole roast held in a blast chiller (CM2); whole roast loosely wrapped and held at 4 degrees C (CM3); and whole roasts (three per bag) held at 4 degrees C (CM4). The roasts were analyzed for C. perfringens using Shahidi-Ferguson perfringens agar and anaerobic incubation (37 degrees C, 24 h). None of the cooling methods met the amended 2001 U.S. Food and Drug Administration Food Code guidelines for safe cooling of potentially hazardous foods. Times taken for roasts to cool from 57 to 21 degrees C using CM1, CM2, CM3, and CM4 were 2.27, 3.11, 6.22, and 8.71 h, respectively. Times taken for roasts (21 degrees C) to reach 5 degrees C ranged from 6.33 (CM1) to 19.45 h (CM4). Based on initial numbers of C. perfringens, no growth occurred in roasts cooled by CM1 or CM2, whereas numbers increased by 1.5 and 4.0 log in whole roasts cooled via CM3 and CM4, respectively. These findings indicate that certain food service cooling methods for whole cooked turkey roasts may result in proliferation of C. perfringens and increase the risk of foodborne illness by this pathogen.

Combining pediocin (ALTA 2341) with postpackaging thermal pasteurization for control of Listeria monocytogenes on frankfurters.

Frankfurters packaged in 1-link, 5-link, or 10-link packages were surface-inoculated with a five-strain mixture of Listeria monocytogenes (3.40 or 5.20 log CFU/g) after treatments with 3,000 arbitrary units (AU) or 6,000 AU pediocin (in ALTA 2341) per link. The frankfurters were vacuum packaged, after which the packages were heated in hot water at 71, 81, or 96 degrees C for 30, 60, or 120 s. L. monocytogenes was enumerated following the treatments. Selected treatments were subsequently evaluated during storage at 4, 10, and 25 degrees C for up to 12 weeks. L. monocytogenes was reduced by all treatments, but 81 degrees C or more for at least 60 s in combination with pediocin (Pdn-6000) was necessary to achieve a 50% reduction of initial inoculations. Heat treatments were most effective for 1-link packages and least effective for 10-link packages. Little or no growth of L. monocytogenes occurred on frankfurters for 12 weeks at 4 or 10 degrees C, and for 12 days at 25 degrees C. Generally, the treatments mentioned above did not significantly (P > 0.05) affect the sensory qualities of frankfurters. Therefore, pediocin (in ALTA 2341) in combination with postpackaging thermal treatment offers an effective treatment combination for improved control of L. monocytogenes on frankfurters.

Combining pediocin with postpackaging irradiation for control of Listeria monocytogenes on frankfurters.

Frankfurters, in 1-link, 5-link, or 10-link packages, were surface inoculated with a five-strain mixture of Listeria monocytogenes (3.40 or 5.20 log CFU/g) after treatment with 3,000 arbitrary units (AU) or 6,000 AU of pediocin (in ALTA 2341) per link. The frankfurters were vacuum packaged, after which the 1-link and 5-link packages were irradiated at 1.2 or 2.3 kGy and the 10-link packages were irradiated at 1.4 or 3.5 kGy. L. monocytogenes was enumerated following the treatments. Selected treatments were subsequently evaluated during storage at 4, 10, and 25 degrees C for up to 12 weeks. Combination of pediocin with postpackaging irradiation at 1.2 kGy or more was necessary to achieve a 50% reduction of L. monocytogenes on frankfurters in 1-link or 5-link packages. The combination of 6,000 AU of pediocin and irradiation at 2.3 kGy or more was effective in all package sizes for inhibition of the pathogen for 12 weeks at 4 or 10 degrees C. There was a synergistic effect between pediocin and irradiation for inhibition of L. monocytogenes. Storage at 4 degrees C enhanced the antilisterial effects of the treatment combinations, with little or no growth of the pathogen in 1-link or 5-link packages during 12 weeks of storage. In general, these treatments did not affect the sensory quality of frankfurters.

Radiation resistance and virulence of Listeria monocytogenes Scott A following starvation in physiological saline.

The influence of starvation on the resistance of Listeria monocytogenes Scott A to electron beam irradiation in 0.85% (wt/vol) NaCl (saline) and in ground pork was investigated. Exponential- or stationary-phase cells (control) were grown at 35 degrees C in tryptic soy broth supplemented with 0.6% yeast extract. Washed cells were starved for 12 days in saline, and virulence of the pathogen was evaluated at 0, 8, and 12 days during starvation. Samples of saline and irradiation-sterilized ground pork, inoculated with control or starved cells, were irradiated at doses ranging from 0.0 to 2.5 kGy. L. monocytogenes survivors were determined by plating diluted samples of saline or pork on tryptic soy agar supplemented with 0.6% yeast extract and counting bacterial colonies following incubation (35 degrees C, 48 h). Virulence of starved cells and control was not significantly different (P > 0.05). Cells exhibited the highest radiation resistance at 8 days of starvation. Irradiation (0.5 kGy) in saline resulted in approximately 7.14, 5.55, and 2.38 log reduction in exponential, stationary, and starved cells, respectively. Irradiation of ground pork at 2.5 kGy reduced controls by approximately 6.0 log, whereas starved cells were reduced by only 3.8 log. Starved cells consistently exhibited higher irradiation D10-values than controls (P < 0.05). D10-values for exponential, stationary, and starved cells were 0.07, 0.09, and 0.21 kGy and 0.35, 0.42, and 0.66 kGy in saline and ground pork, respectively. These results indicate that starvation cross-protects L. monocytogenes Scott A against radiation inactivation and should be considered when determining this pathogen's irradiation D-value.

A predictive model to determine the effects of temperature, sodium pyrophosphate, and sodium chloride on thermal inactivation of starved Listeria monocytogenes in pork slurry.

The effects and interactions of 27 combinations of heating temperature (57.5 to 62.5 degrees C), sodium pyrophosphate (SPP) level (0 to 0.5%, wt/vol), and salt (NaCl) level (0 to 6%, wt/vol) on the thermal inactivation of starved Listeria monocytogenes ATCC 19116 in pork slurry were investigated. A split-split plot experimental design was used to compare all 27 combinations. L. monocytogenes survivors were enumerated on tryptic soy agar supplemented with 0.6% yeast extract. The natural logarithm (loge) of the means of decimal reduction times (D-values) were modeled as a function of temperature, SPP level, and NaCl level. Increasing concentrations of SPP or NaCl protected starved L. monocytogenes from the destructive effect of heat. For example, D-values for the pathogen at 57.5 degrees C in pork slurry with 0, 3, and 6% NaCl were 2.79, 7.75, and 14.59 min, respectively. All three variables interacted to affect the thermal inactivation of L. monocytogenes. A mathematical model describing the combined effect of temperature, SPP level, and NaCl level on the thermal inactivation of starved L. monocytogenes was developed. There was strong correlation (R2 = 0.97) between loge D-values predicted by the model and those observed experimentally. The model can predict D-values for any combination of variables that falls within the range of those tested. This predictive model can be used to assist food processors in designing thermal processes that include an adequate margin of safety for the control of L. monocytogenes in processed meats.

Quality characteristics of irradiated ready-to-eat breast rolls from turkeys fed conjugated linoleic acid.

The objective of this study was to determine the effect of irradiation on the quality of ready-to-eat (RTE) breast rolls from turkeys fed conjugated linoleic acid (CLA). The oxidative stability of RTE turkey rolls was improved by the dietary CLA treatment. Irradiation increased the production of acetaldehyde, 3-methyl-butanal, 2-methyl-butanal, and total volatiles in turkey rolls but had little effect on other aldehydes. Irradiation also produced new volatiles, including sulfur compounds, not detected in nonirradiated turkey breast rolls. We detected significantly higher amounts of alkanes with nine or higher carbons in irradiated samples than in nonirradiated samples. Irradiation increased the redness of RTE turkey breast rolls, but the degree of redness and the amount of total volatiles decreased with storage. CLA treatment lowered the redness (a*) and increased the lightness (L*) of RTE turkey breast rolls during the entire storage period. Sensory evaluation revealed that irradiation produced off-flavor, but CLA and irradiation did not influence the texture and juiciness of RTE turkey breast rolls. Consumers did not like the off-flavor but preferred the color induced by irradiation to nonirradiated RTE turkey breast rolls.

A novel strictly anaerobic recovery and enrichment system incorporating lithium for detection of heat-injured Listeria monocytogenes in pasteurized milk containing background microflora.

Heat-injured cells of Listeria monocytogenes were recovered from heated raw milk containing noninjured Enterococcus faecium by combining a simple method for obtaining strict anaerobiosis with a novel enrichment broth, Penn State University broth (PSU broth). Strictly anaerobic conditions were rapidly achieved by adding 0.5 g of filter-sterilized cysteine per liter to PSU broth and then purging the preparation with N2 gas. Little resuscitation or growth occurred in strictly anaerobic PSU broth without lithium chloride because of overgrowth by E. faecium. The growth of E. faecium decreased dramatically with increasing LiCl concentration; LiCl concentrations of 8 and 10 g/liter were completely bacteriostatic. The mechanism of inhibition by LiCl appeared to involve competition with the divalent cations Ca2+ and Mg2+. Heat-injured L. monocytogenes consistently recovered and grew rapidly in strictly anaerobic PSU broth containing 4, 6, or 7 g of LiCl per liter. The use of strictly anaerobic PSU broth containing 7 g of LiCl per liter permitted detection of severely heat-injured L. monocytogenes in one simple recovery-enrichment step by eliminating oxygen toxicity and inhibiting the growth of background microflora, without preventing the resuscitation and subsequent growth of heat-injured L. monocytogenes. L. monocytogenes heated in raw milk at 62.8 degrees C for 10, 15, and 20 min could be consistently recovered from strictly anaerobic PSU broth enrichment cultures at 30 degrees C after 48, 96, and 144 h, respectively, and hence, use of PSU broth may result in better recovery of both injured and noninjured cells from foods than currently used U.S. Department of Agriculture and Food and Drug Administration preenrichment procedures.

Destruction of gram-negative food-borne pathogens by high pH involves disruption of the cytoplasmic membrane.

High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs within 15 s, whereas L. monocytogenes decreased by only 1 log in 10 min. There was a very strong correlation between the initial rate of release of material with A260 and death rate of the gram-negative pathogens (r = 0.997). At pH 12, gram-negative test cells appeared collapsed and showed evidence of lysis while gram-positive L. monocytogenes did not, when observed by scanning and transmission electron microscopy. It was concluded that destruction of gram-negative food-borne pathogens by high pH involves disruption of the cytoplasmic membrane.

Effects of growth temperature and strictly anaerobic recovery on the survival of Listeria monocytogenes during pasteurization.

Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-0.6% yeast extract (TSBYE) or sterile, whole milk and heated at 62.8 degrees C in sealed thermal death time tubes. Severely heat-injured cells were recovered in TSBYE within sealed thermal death time tubes because of the formation of reduced conditions in the depths of the TSBYE. Also, the use of strictly anaerobic Hungate techniques significantly increased recovery in TSBYE containing 1.5% agar compared with aerobically incubated controls. The exogenous addition of catalase, but not superoxide dismutase, slightly increased the recovery of heat-injured cells in TSBYE containing 1.5% agar incubated aerobically. Growth of cells at 43 degrees C caused a greater increase in heat resistance as compared with cells heat shocked at 43 degrees C or cells grown at lower temperatures. Growth of L. monocytogenes at 43 degrees C and enumeration by the use of strictly anaerobic Hungate techniques resulted in D62.8 degrees C values that were at least sixfold greater than those previously obtained by using cells grown at 37 degrees C and aerobic plating. Results indicate that, under the conditions of the present study, high levels of L. monocytogenes would survive the minimum low-temperature, long-time treatment required by the U.S. Food and Drug Administration for pasteurizing milk. The possible survival of low levels of L. monocytogenes during high-temperature, short-time pasteurization and enumeration of injured cells by recovery on selective media under strictly anaerobic conditions are discussed.