Reduction and survival of Listeria monocytogenes in ready-to-eat meats after irradiation

A five-strain Listeria monocytogenes culture was inoculated onto six different types of ready-to-eat (RTE) meats (frankfurters, ham, roast beef, bologna, smoked turkey with lactate, and smoked turkey without lactate). The meats were vacuum packed and stored at 4 degrees C for 24 h prior to irradiation. Populations of L. monocytogenes were recovered by surface plating on nonselective and selective media. The margins of safety studied include 3-log (3D) and 5-log (5D) reduction of pathogenic bacteria to achieve an optimal level of reduction while retaining organoleptic qualities of the meats. A 3-log reduction of L. monocytogenes was obtained at 1.5 kGy when nonselective plating medium was used. The dosages for 3-log reduction were 1.5 kGy for bologna, roast beef, and both types of turkey and 2.0 kGy for frankfurters and ham on the basis of use of selective medium. The D10-values ranged from 0.42 to 0.44 kGy. A 5-log reduction of L. monocytogenes was obtained at 2.5 kGy with nonselective medium. With selective medium, the dosages were 2.5 kGy for bologna, roast beef, and both types of turkey and 3.0 kGy for frankfurters and ham. Survival of L. monocytogenes in the same RTE meat types after irradiation was also studied. Meats were inoculated with 5 log L. monocytogenes per g and irradiated at doses of 2.0 and 4.0 kGy. Recovery of the surviving organisms was observed during storage at temperatures of 4 and 10 degrees C for 12 weeks. Preliminary results showed no growth in meats irradiated at 4.0 kGy. Survivors were observed for irradiated meats at 2.0 kGy stored at 10 degrees C after the second week. No growth was observed in samples irradiated at 2.0 kGy stored at 4 degrees C until the fifth week.     

Control of Listeria Monocytogenes by Lauric Arginate on Frankfurters Formulated with or without Lactate/Diacetate

ABSTRACT:  Listeria monocytogenes  (Lm) is a food safety concern that can be associated with ready-to-eat (RTE) meat and poultry products because of its persistence in the processing environment. Listeriosis has a fatality rate of 28% in immuno-compromised individuals. RTE meats receive a lethal heat treatment but may become contaminated by Lm after this treatment. Federal regulators and manufacturers of RTE meats are working to find additional ways to control postprocess contamination by Lm in RTE meats. This research was initiated to validate combinations of antimicrobials that would produce an immediate lethality of at least 1 log of Lm on artificially contaminated frankfurters, and also suppress Lm growth to less than 2 logs throughout the extended shelf life at refrigerated temperatures (4 °C). Based on our studies, 22-ppm lauric arginate (LAE, ethyl-N-dodecanoyl-L-arginate hydrochloride) gave more than a 1-log reduction of Lm surface inoculated onto frankfurters within 12 h. The combination of either 1.8%/0.13% or 2.1%/0.15% potassium lactate/sodium diacetate (L/D) in combination with 22 ppm LAE caused more than a 2-log reduction at 12 h. Storage studies revealed that complementary interactions of L/D and LAE also met the 2nd requirement. This combination initially reduced Lm by 2 logs and suppressed growth to less than 2 logs even at the end of the 156-d storage life for frankfurters. These results confirmed that the combination of L/D with LAE as a postprocessing–prepackaging application could be useful in complying with the USDA's Alternative 1 that requires validation for the control of Lm on RTE frankfurters.     

Competitive inhibition of Listeria monocytogenes in ready-to-eat meat products by lactic acid bacteria

Forty-nine strains of lactic acid bacteria (LAB), isolated from commercially available ready-to-eat (RTE) meat products, were screened for their ability to inhibit the growth of Listeria monocytogenes at refrigeration (5 degrees C) temperatures on agar spot tests. The three most inhibitory strains were identified as Pediococcus acidilactici, Lactobacillus casei, and Lactobacillus paracasei by 16S rDNA sequence analysis. Their antilisterial activity was quantified in associative cultures in deMan Rogosa Sharpe (MRS) broth at 5 degrees C for 28 days, resulting in a pathogen reduction of 3.5 log10 cycles compared to its initial level. A combined culture of these strains was added to frankfurters and cooked ham coinoculated with L. monocytogenes, vacuum packaged, and stored at 5 degrees C for 28 days. Bacteriostatic activity was observed in cooked ham, whereas bactericidal activity was observed in frankfurters. Numbers of L. monocytogenes were 4.2 to 4.7 log10 and 2.6 log10 cycles lower than controls in frankfurters and cooked ham, respectively, after the 28-day refrigerated storage. In all cases, numbers of LAB increased by only 1 log10 cycle. The strain identified as P. acidilactici was possibly a bacteriocin producer, whereas the antilisterial activity of the other two strains was due to the production of organic acids. There was no significant difference (P > 0.05) in the antilisterial activity detected in frankfurters whether the LAB strains were used individually or as combined cultures. Further studies over a 56-day period indicated no impact on the quality of the product. This method represents a potential antilisterial intervention in RTE meats, because it inhibited the growth of the pathogen at refrigeration temperatures without causing sensory changes.     

Survival and recovery of Listeria monocytogenes on ready-to-eat meats inoculated with a desiccated and nutritionally depleted dustlike vector

Dust from construction was theorized to serve as a vector for L. monocytogenes transmission to ready-to-eat (RTE) meats after heat processing but before packaging. A five-strain Listeria monocytogenes culture including serotype 4b was continually stressed on a sand vector under four sets of nutritionally depleted and dry conditions to simulate postprocessing contamination by dustlike particulates. The stresses included that associated with sand stored at different temperatures (10 and 22 degrees C) and levels of humidity (40% relative humidity [RH], 88% RH, or complete desiccation). Irradiated RTE meats, including frankfurters, bologna, chopped ham, and deli-style roast beef, were inoculated with the L. monocytogenes-contaminated sand every 2 to 3 days over a period of 1 1/2 months. After inoculation, the RTE meats were vacuum packed and stored at 4 degrees C for 24 h. Populations of L. monocytogenes were enumerated by surface plating on nonselective and selective media to recover cells on the basis of the different stresses presented (osmotic or antibiotic). L. monocytogenes was demonstrated to be capable of surviving on the sand vector for > 151 days at 10 degrees C and 88% RH, 136 days at 10 degrees C and 0% RH, 73 days at 22 degrees C and 40% RH, and 82 days at 22 degrees C and 0% RH. These results show that under the most conservative scenario, the 73-day-old L. monocytogenes-contaminated sand was able to attach to and be recovered from the RTE meats. This study illustrated that dust contaminated with L. monocytogenes, once in contact with meat surfaces, can survive and grow, posing a health hazard to consumers.     

Modeling the impact of chlorine on the behavior of Listeria monocytogenes on ready-to-eat meats

Listeria monocytogenes (Lm) continues to pose a food safety hazard in ready-to-eat (RTE) meats due to potential cross-contamination. Chlorine is commonly used to sanitize processing equipment and utensils. However, Lm may survive the treatment and then contaminate food products. The objective of this study was to characterize the behavior of chlorine-exposed Lm on RTE ham during refrigerated storage. A two strain cocktail of Lm serotype 4b was pre-treated with chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto the surface of RTE ham to obtain an inoculum of about 3.0 log CFU/g. The inoculated ham samples were stored at 4, 8, and 16 °C, and Lm was enumerated periodically during the storage. The growth characteristics (lag time and growth rate) of Lm were estimated using the DMFit software. The results indicated that Lm growth was suppressed by the chlorine treatment. At 4 °C, the lag time of Lm with no (0 ppm) chlorine exposure (4.2 days) was shorter than those exposed to 25 ppm (5.4 days) and 50 ppm (6.8 days). The lag time decreased with the increase of temperature, e.g., at 25 ppm, the lag times were 5.2, 3.8 and 2.6 days for 4, 8 and 16 °C, respectively, and increased with the increase of chlorine concentration, e.g., at 16 °C, the lag times were 1.2, 2.6 and 4.0 days for 0, 25 and 50 ppm, respectively. However, growth rate increased with the increase of temperature and decreased with the increase of chlorine concentration. The lag time and growth rate as a function of chlorine concentration and temperature can be described using a modified Ratkowsky model and a modified Zwietering model, respectively. The results showed that the growth of Lm on RTE ham was delayed by pre-exposure to chlorine (at ≤50 ppm). The predictive models developed will contribute to microbial risk assessments of RTE meats.     

Use of vacuum-steam-vacuum and ionizing radiation to eliminate Listeria innocua from ham

Listeria spp. are a frequent postprocess contaminant of ready-to-eat (RTE) meat products, including ham. Vacuum-steam-vacuum (VSV) technology has been used successfully to eliminate Listeria innocua from hot dogs. Ionizing radiation can eliminate Listeria spp. from RTE meats. However, the excessive application of either technology can cause changes in product quality, including structural changes, changes in cure color (redness), and lipid oxidation. In this study, two cycles of VSV were combined with 2.0 kGy of ionizing radiation to obtain 4.40- and 4.85-log10 reductions of L. innocua on ham meat and skin, respectively. The use of both treatments resulted in an additive, as opposed to synergistic, reduction of L. innocua on ham. The combination treatment did not cause statistically significant changes in product structure, color (redness), or lipid oxidation.     

Effects of Lactic Acid on the Growth Characteristics of Listeria monocytogenes on Cooked Ham Surfaces

The surfaces of ready-to-eat meats are susceptible to postprocessing contamination by Listeria monocytogenes. This study examined and modeled the growth characteristics of L. monocytogenes on cooked ham treated with lactic acid solutions (LA). Cooked ham was inoculated with L. monocytogenes (ca. 10(3) CFU/g), immersed in 0, 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0% LA for 30 min, vacuum packaged, and stored at 4, 8, 12, and 16°C. LA immersion resulted in <0.7 log CFU/g immediate reduction of L. monocytogenes on ham surfaces, indicating the immersion alone was not sufficient for reducing L. monocytogenes. During storage, no growth of L. monocytogenes occurred on ham treated with 1.5% LA at 4 and 8°C and with 2% LA at all storage temperatures. LA treatments extended the lag-phase duration (LPD) of L. monocytogenes and reduced the growth rate (GR) from 0.21 log CFU/day in untreated ham to 0.13 to 0.06 log CFU/day on ham treated with 0.5 to 1.25% LA at 4°C, whereas the GR was reduced from 0.57 log CFU/day to 0.40 to 0.12 log CFU/day at 8°C. A significant extension of the LPD and reduction of the GR of L. monocytogenes occurred on ham treated with >1.25% LA. The LPD and GR as a function of LA concentration and storage temperature can be satisfactorily described by a polynomial or expanded square-root model. Results from this study indicate that immersion treatments with >1.5% LA for 30 min may be used to control the growth of L. monocytogenes on cooked meat, and the models would be useful for selecting LA immersion treatments for meat products to achieve desired product safety.     

Comparison of electrolyzed oxidizing water with other antimicrobial interventions to reduce pathogens on fresh pork

To date, the effectiveness of electrolyzed oxidizing (EO) water against bacteria associated with fresh pork has not been determined. Using a hand-held, food-grade garden sprayer, distilled water (W), chlorinated water (CL; 25 ppm), 2% lactic acid (LA), acidic EO water (EOA), or "aged" acidic EO water (AEOA; stored at 4 °C for 24 h) was sprayed (15 s) onto pork bellies inoculated with feces containing Listeria monocytogenes (LM), Salmonella typhimurium (ST), and Campylobacter coli (CC). Remaining bacterial populations were determined immediately following treatment, after 2 days of aerobic storage, and again after 5 days of vacuum-packaged, refrigerated storage (day 7). While LA and EOA significantly reduced (p<0.05) populations of CC at days 0 and 7, there was no significant difference (p>0.05) between antimicrobial treatments when applied to pork inoculated with ST or LM. This study demonstrates that a 15-s spray with EOA has the ability to reduce CC associated with fresh pork surfaces. However, longer contact times may be necessary to reduce other microbial contaminants.     

Attachment of Listeria monocytogenes on ready-to-eat meats

Five individual strains of Listeria monocytogenes and a mixed cocktail of all five were studied for attachment on frankfurters, ham, bologna, and roast beef relative to their cell surface characteristics. The ratio of strongly attached (sessile) L. monocytogenes cells compared with total (sessile and planktonic) attached cells on ready-to-eat meats was also determined. Because bacterial cell surfaces were characterized by net negative charge and hydrophobicity, electrostatic interaction chromatography and cationized ferritin methods were chosen to study net negative charge distribution on the bacterial cell surface, whereas hydrophobic interaction chromatography and contact angle measurement were used to examine the cell surface hydrophobicity. No differences (P > 0.05) were observed in cell surface charge or cell surface hydrophobicity among strains. Approximately 84 to 87% L. monocytogenes were found to attach strongly to ready-to-eat meats within 5 min. No differences (P > 0.05) were found among strains or among meats. Micrographs observed from scanning electron microscopy showed no differences among the strains but showed a difference in age of cells (mixed culture) in terms of surface negative charge distribution. More surface negatively charged sites were observed at 0 and 7 days and much fewer at 3 days during storage of washed, harvested cells in buffer at 4 degrees C (aged cells under cold and nutrient deprivation), indicating a possible change in cell surface properties. Because no difference in strains was observed, the contact angle measurement study was carried out with the five-strain mixed culture. The surface hydrophobicity increased in frankfurters, decreased in roast beef, and was unchanged in ham and bologna as a result of inoculation.     

Consumer knowledge and use of open dates: results of a WEB-based survey

Consumers are relying increasingly on ready-to-eat (RTE) foods because they are convenient, quick, and easy. Open dates let consumers know by which date to purchase or use RTE foods for best quality. To further characterize consumer knowledge and use of open dates for specific refrigerated RTE foods (smoked seafood, cooked crustaceans, bagged salads, prewashed cut produce, soft cheeses, frankfurters, deli meats, fermented sausages, and deli salads), we conducted a nationally representative web-enabled survey (n=2060). Before purchasing RTE foods, 48 to 68% of respondents check open dates all or most of the time. Before preparing RTE foods, 43 to 64% of respondents check open dates all or most of the time. Nearly two-thirds of respondents reported that their senses were the most important factors in deciding whether to eat a refrigerated food, which is an unsafe practice. About one-third of respondents reported that an open date is the most important factor in deciding whether to eat a refrigerated food. Many respondents, however, do not understand the meanings of the different types of dates. Only 18% correctly defined the use-by date. The findings suggest consumers could benefit from education regarding open dates and recommended storage times for RTE foods.     

Postpackage pasteurization of ready-to-eat deli meats by submersion heating for reduction of Listeria monocytogenes

A mixed cocktail of four strains of Listeria monocytogenes was resuspended in product purge and added to a variety of ready-to-eat (RTE) meat products, including turkey, ham, and roast beef. All products were vacuum sealed in shrink-wrap packaging bags, massaged to ensure inoculum distribution, and processed by submersion heating in a precision-controlled steam-injected water bath. Products were run in pairs at various time-temperature combinations in either duplicate or triplicate replications. On various L. monocytogenes-inoculated RTE deli meats, we were able to achieve 2- to 4-log cycle reductions when processed at 195 degrees F (90.6 degrees C), 200 degrees F (93.3 degrees C), or 205 degrees F (96.1 degrees C) when heated from 2 to 10 min. High-level inoculation with L. monocytogenes (approximately 10(7) CFU/ml) ensured that cells infiltrated the least processed surface areas, such as surface cuts, folds, grooves, and skin. D- and z-value determinations were made for the Listeria cocktail resuspended in product purge of each of the three meat categories. However, reduction of L. monocytogenes in product challenge studies showed much less reduction than was observed during the decimal reduction assays and was attributed to a combination of surface phenomena, including surface imperfections, that may shield bacteria from the heat and the migration of chilled purge to the product surface. The current data indicate that minimal heating regimens of 2 min at 195 to 205 degrees F can readily provide 2-log reductions in most RTE deli meats we processed and suggest that this process may be an effective microbial intervention against L. monocytogenes on RTE deli-style meats.     

Stability of electrolyzed oxidizing water and its efficacy against cell suspensions of Salmonella typhimurium and Listeria monocytogenes

Electrolyzed oxidizing (EO) water has proved to be effective against foodborne pathogens attached to cutting boards and poultry surfaces and against spoilage organisms on vegetables; however, its levels of effectiveness against Listeria monocytogenes and Salmonella Typhimurium in cell suspensions have not been compared with those of other treatments. In this study, the oxidation reduction potentials (ORPs), chlorine concentrations, and pHs of acidic and basic EO water were monitored for 3 days at 4 and 25 degrees C after generation. There were no differences between the pHs or ORPs of acidic and basic EO waters stored at 4 or 25 degrees C. However, the free chlorine concentration in acidic EO water stored at 4 degrees C increased after 24 h. In contrast, the free chlorine concentration in acidic EO water stored at 25 degrees C decreased after one day. Cell suspensions of Salmonella Typhimurium and L. monocytogenes were treated with distilled water, chlorinated water (20 ppm), acidified chlorinated water (20 ppm, 4.5 pH), acidic EO water (EOA), basic EO water (EOB), or acidic EO water that was "aged" at 4 degrees C for 24 h (AEOA) for up to 15 min at either 4 or 25 degrees C. The largest reductions observed were those following treatments carried out at 25 degrees C. EOA and AEOA treatments at both temperatures significantly reduced Salmonella Typhimurium populations by > 8 log10 CFU/ml. EOA and AEOA treatments effectively reduced L. monocytogenes populations by > 8 log10 CFU/ml at 25degrees C. These results demonstrate the stability of EO water under different conditions and that EO water effectively reduced Salmonella Typhimurium and L. monocytogenes populations in cell suspensions.     

Effect of Gamma Radiation on Furan Formation in Ready-to-Eat Products and their Ingredients

ABSTRACT:  Besides meat as the major component, ready-to-eat (RTE) meat and poultry products often contain ingredients such as Na-ascorbate, Na-erythorbate, glucose, honey, corn syrup, and Na-nitrite. Furan is a potential carcinogen and information is needed on its formation in irradiated RTE products. In the present study, we investigated the generation of irradiation-induced furan in aqueous solutions of those ingredients, and in 9 RTE food products (8 meat and poultry-based and 1 vegetable burger). Irradiation at doses up to 4.5 kGy induced formation of furan in aqueous solutions of Na-ascorbate, Na-erythorbate, glucose, honey, and corn syrup. Addition of Na-nitrite into these solutions prior to irradiation completely eliminated, or significantly reduced, furan formation. Most of the nonirradiated RTE products contained less than 1 ng/g of furan, except for beef and turkey frankfurters which contained 6 to 8 ng/g furan. Exposure of RTE food products to 4.5 kGy radiation in the nonfrozen state (5 °C) or to 10 kGy radiation in the frozen state (−18 °C) did not significantly increase furan levels in most of the samples. Furthermore, the irradiation treatments reduced furan levels in samples (that is, frankfurters) that contained more than 3 ng/g of furan. Our results suggested that irradiation induces furan formation in solutions of many RTE food ingredients, but not in RTE meat and poultry products themselves.     

Lipolytic and proteolytic properties of dry-cured boneless hams ripened in modified atmospheres

We studied proteolytic and lipolytic properties of dry-cured boneless ham (porcine quadriceps femoris) made with chilled (10°C, 48 h) or frozen/thawed meat (frozen at -20°C frozen for 90 days and followed by thawing at 10°C for 48 h) were determined. Dry-cured meats were stored in modified atmosphere packages (100% N(2) and a mixture of 75% N(2)+25% CO(2)) at 15°C with the intention of reducing ripening space. Results showed that dry-cured hams made with frozen/thawed raw meat had more salt, volatile fatty acids and free fatty acid content after salting and smoking. Whereas, samples prepared with chilled meats contained more nitrogenous compounds (water-soluble nitrogen, non-protein nitrogen, and free amino acids). Volatile and free fatty acid contents in all samples significantly increased with storage. Acetic acid was the predominant volatile fatty acid. To confirm lipolytic activity in dry-cured ham stored in modified atmospheres, we calculated the lipolytic coefficient. The lipolytic coefficients of all samples were positive values and significantly (P<0.05) increased with storage indicating lipolysis in samples were still active. Furthermore, nitrogenous compounds in dry-cured ham significantly (P<0.05) increased with storage indicating proteolysis in samples were not affected by modified atmosphere storage. Aerobic, anaerobic and lactic acid bacteria counts in dry-cured meats were stable to modified atmospheres storage for 20 weeks at 15°C. Flavor, texture and color score in sensory evaluation for dry-cured ham made with chilled meat were significantly higher than that made with frozen/thawed meat. All samples had high overall acceptance scores in sensory evaluation. Results in this study suggested that dry-cured boneless ham stored in modified atmospheres for 20 weeks at 15°C was another feasibility to ripen the meat without affecting lipolysis, proteolysis, microbiology and sensory quality.     

Survival and growth of Clostridium perfringens in commercial no-nitrate-or-nitrite-added (natural and organic) frankfurters, hams, and bacon

The popularity of "preservative-free" foods among consumers has stimulated rapid growth of processed meats manufactured without sodium nitrite. The objective of this study was to quantify the potential for Clostridium perfringens growth in commercially available processed meats manufactured without the direct addition of nitrite or nitrate. Commercial brands of naturally cured, no-nitrate-or-nitrite-added frankfurters (10 samples), hams (7 samples), and bacon (9 samples) were obtained from retail stores and challenged with a three-strain inoculation (5 log CFU/g) of C. perfringens. Reduced inhibition (P < 0.05) was observed in seven brands of frankfurters, six brands of hams, and four brands of bacon when compared with each respective sodium nitrite-added control. In naturally cured and truly uncured commercial frankfurters, growth over time was approximately 4.7 log, while conventionally cured frankfurters exhibited growth at 1.7 log. Naturally cured ham and bacon products exhibited growth at 4.8 and 3.4 log, respectively, while their conventionally cured counterparts exhibited growth at 2.6 and 2.3 log, respectively. These products also demonstrated variation in growth response. The results indicate that commercially available natural/organic naturally cured meats have more potential for growth of this pathogen than do conventionally cured products. Natural and organic processed meats may require additional protective measures in order to consistently provide the level of safety from bacterial pathogens achieved by conventionally cured meat products, and which is expected by consumers.     

Varying the temperature of the liquid used for high-pressure processing of prerigor pork: effects on fresh pork quality, myofibrillar protein solubility, and frankfurter textural properties

The objective was to evaluate high-pressure processing (HPP) with varying liquid (water) temperatures on pork quality and textural properties of frankfurters. HPP pressurization liquid temperatures were 15.5 °C (HPP Low) and 29.4 °C (HPP Med). Analyses were conducted using paired boneless loins and paired boneless hams. Loins were evaluated for pH, purge loss, objective color, subjective color, firmness; and changes in color after a bloom period. Eight independent batches (2 batches each of HPP Low, paired untreated, HPP Med, and paired untreated) of frankfurters were manufactured from the outside portion of the ham and the knuckle. Both HPP treatments resulted in higher (P < 0.05) ultimate pH and less (P < 0.05) purge loss of the loin. Loin tenderness was not different among either HPP treatment temperature groups when compared to untreated controls except HPP Med chops were more tender (P = 0.02) than untreated controls. Salt-soluble protein extractability of inside ham muscles was lower (P < 0.05) for both HPP treatment levels when compared to untreated controls, but was not different between the 2 HPP treatment levels. Textural properties of frankfurters were not different for either HPP treatment group when compared to its respective untreated control for any parameter except springiness. HPP Low frankfurters had lower (P = 0.10) springiness values than untreated controls. Fracturability of HPP Med samples was lower (P = 0.12) than untreated controls. Overall, HPP caused higher ultimate pH and increased water-holding capacity, but did not affect tenderness of fresh meat or textural properties of frankfurters. PRACTICAL APPLICATION: HPP can be used on prerigor pork as means to improve fresh pork quality. Loins from HPP-treated pork sides had higher ultimate pH values and less package purge loss. Tenderness values were not affected positively or negatively by HPP treatment. The high pH and water-holding capabilities of treated samples have positive implications for further processing applications. Frankfurter textural properties suggest emulsified products can be made with pressurized pork without sacrifice to the textural profile.     

Technologies and Mechanisms for Safety Control of Ready-to-eat Muscle Foods: An Updated Review

Ready-to-eat (RTE) muscle foods refer to a general category of meat and poultry products that are fully cooked and consumable without reheating. These products, including whole and sliced pork, beef, turkey, chicken, and variety of meats, in the forms of ham, roast, rolls, sausage, and frankfurter, are widely available in the delicatessen section of retail stores or various food service outlets. However, difficulties in avoidance of contamination by foodborne pathogens, notably Listeria monocytogenes, during product postlethality repackaging render RTE meats labile to outbreaks. Accordingly, the USDA-FSIS has established processing guidelines and regulations, which are constantly updated, to minimize foodborne pathogens in RTE products. Technologies that complement good manufacturing practice have been developed to control RTE meat safety. Among them, various antimicrobial product formulations, postpackaging pasteurization (thermal and nonthermal), and antimicrobial packaging are being used. Through these efforts, outbreaks linked to RTE meat consumption have substantially reduced in recent years. However, the pervasive and virulent nature of L. monocytogenes and the possible presence of other cold-tolerant pathogens entail continuing developments of new intervention technologies. This review updates existing and emerging physical and chemical methods and their mode of action to inactivate or inhibit threatening microorganisms in RTE muscle foods.     

Growth of Listeria monocytogenes in different retail delicatessen meats during simulated home storage

Delicatessen meats are reported to be the leading vehicle of foodborne listeriosis in the United States. Listeria monocytogenes can reach high numbers in these products during storage, and the growth rate is largely dictated by product formulation and storage temperature. To assess the impact of product age on Listeria growth, five commercial brands each of cured and uncured turkey breast, ham, and roast beef (three lots per brand) were sliced (approximately 25 g per slice) at the beginning of the shelf life, the midpoint, and the last allowable day of sale, surface inoculated with an eight-strain cocktail of L. monocytogenes (approximately 40 CFU/g), and then quantitatively examined for Listeria, lactic acid bacteria, and mesophilic aerobic bacteria during aerobic storage at 4, 7, or 10°C. As expected, L. monocytogenes grew faster in deli meats without rather than with Listeria inhibitors (lactate and/or diacetate) and at the highest storage temperature (10°C). Lag-phase durations for L. monocytogenes in deli meats with and without Listeria inhibitors were 9.21, 6.96, and 5.00 and 6.35, 3.30, and 2.19 days at 4, 7, and 10°C, respectively. Generation times for L. monocytogenes in deli meats with and without Listeria inhibitors were 1.59, 1.53, and 0.85 and 0.94, 0.50, and 0.36 at 4, 7, and 10°C, respectively. Maximum population densities for L. monocytogenes in deli meats with and without Listeria inhibitors were 5.26, 5.92, and 5.97 and 8.47, 8.96 and 9.34 log CFU/g at 4, 7, and 10°C, respectively. Although lactate and diacetate suppressed L. monocytogenes growth, the extent of inhibition differed, ranging from total inhibition in roast beef to only partial inhibition in ham and cured turkey. Listeria growth was also impacted by lot-to-lot variation in the concentrations of Listeria inhibitors, product pH, and background microflora. These data will be useful for developing recommendations for "best consumed by" dating for deli meats using a risk-based approach.     

重庆市即食食品中单核细胞增生李斯特菌污染监测及初步风险评估

目的 了解重庆市市售即食食品中单核细胞增生李斯特菌(以下简称单增李斯特菌)的污染情况,进行初步风险评估,为预防食源性疾病提供科学依据.方法 2016-2019年对全市39个区县的市售即食食品中的单增李斯特菌进行监测,并用半定量微生物风险评估方法,初步评估重庆市即食食品中单增李斯特菌的风险.结果 重庆市2 680份即食食...     

The Effects of Irradiation at 1.6 kGy on Quality Characteristics of Commercially Produced Ham and Pork Frankfurters over Extended Storage

ABSTRACT: Commercially produced sliced ham and all-pork frankfurters were obtained from a national meat processor and irradiated at 1.6 kGy. The samples were evaluated for color, lipid oxidation, odor, flavor, and the production of volatiles over an 8-wk storage period. Irradiation processing did not affect color values for the ham or frankfurters. Lipid oxidation as measured by 2-thiobarbituric acid-reactive substances (TBARS) did not increase for either the ham or frankfurters. Irradiation processing increased off-odor scores for the ham but not for frankfurters. On the other hand, off-flavor scores were not significantly different for ham but were higher in frankfurters after irradiation processing. Dimethyl disulfide content increased as a result of irradiation in both the ham and frankfurters but decreased during the 8-week storage period. Irradiation processing resulted in the formation of new volatile compounds in the ham samples including heptane, trans -1-butyl-2-methylcyclopropanone, 2-octene, and toluene, which were not present in nonirradiated ham. In the case of frankfurters, irradiation treatment resulted in the formation of 2-butanone, which was not present in the nonirradiated frankfurters. Most volatile compounds that were affected by irradiation processing of either the ham or frankfurters were increased when compared with nonirradiated controls. Although color and lipid oxidation (TBARS) did not seem to be affected by irradiation processing at 1.6 kGy, changes in odor, flavor, and the production of volatiles are of concern if irradiation is to be used to control microbial growth in ready-to-eat pork products.