Inhibition of Clostridium perfringens Spore Germination and Outgrowth by Lemon Juice and Vinegar Product in Reduced NaCl Roast Beef

Abstract: Inhibition of Clostridium perfringens spore germination and outgrowth in reduced sodium roast beef by a blend of buffered lemon juice concentrate and vinegar (MoStatin LV1) during abusive exponential cooling was evaluated. Roast beef containing salt (NaCl; 1%, 1.5%, or 2%, w/w), blend of sodium pyro‐ and poly‐phosphates (0.3%), and MoStatin LV1 (0%, 2%, or 2.5%) was inoculated with a 3‐strain C. perfringens spore cocktail to achieve final spore population of 2.5 to 3.0 log CFU/g. The inoculated products were heat treated and cooled exponentially from 54.4 to 4.4 °C within 6.5, 9, 12, 15, 18, or 21 h. Cooling of roast beef (2.0% NaCl) within 6.5 and 9 h resulted in <1.0 log CFU/g increase in C. perfringens spore germination and outgrowth, whereas reducing the salt concentration to 1.5% and 1.0% resulted in >1.0 log CFU/g increase for cooling times longer than 9 h (1.1 and 2.2 log CFU/g, respectively). Incorporation of MoStatin LV1 into the roast beef formulation minimized the C. perfringens spore germination and outgrowth to <1.0 log CFU/g, regardless of the salt concentration and the cooling time. Practical Application: Cooked, ready‐to‐eat meat products should be cooled rapidly to reduce the risk of Clostridium perfringens spore germination and outgrowth. Meat processors are reducing the sodium chloride content of the processed meats as a consequence of the dietary recommendations. Sodium chloride reduces the risk of C. perfringens spore germination and outgrowth in meat products. Antimicrobials that contribute minimally to the sodium content of the product should be incorporated into processed meats to assure food safety. Buffered lemon juice and vinegar can be incorporated into meat product formulations to reduce the risk of C. perfringens spore germination and outgrowth during abusive cooling.     

The effect of high hydrostatic pressure,sodium nitrite and salt concentration on the growth of Listeria monocytogenes on RTE ham and turkey

Growth of Listeria monocytogenes was evaluated for up to 182 days after inoculation on ready-to-eat (RTE) sliced ham and turkey breast formulated with sodium nitrite (0 or 200 ppm), sodium chloride (1.8% or 2.4%), and treated (no treatment or 600 MPa) with high hydrostatic pressure (HHP). HHP at 600 MPa for 3 min resulted in a 3.85–4.35 log CFU/g reduction in L. monocytogenes. With formulations at similar proximate analyses, one of the evaluation days (day 21) without HHP showed significantly greater growth of L. monocytogenes in ham than in turkey breast, but there were no significant differences on other evaluation days or with HHP. There were no differences in growth of L. monocytogenes due to sodium chloride level. Sodium nitrite provided a small, but significant inhibition of L. monocytogenes without HHP, but addition of sodium nitrite did not significantly affect growth of L. monocytogenes with use of HHP.     

Growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham under refrigerated and temperature abuse conditions

This study examined the growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham at refrigerated and abuse temperatures. A five-strain mixture of L. monocytogenes and a native microflora, consisting of Brochothrix spp., isolated from cooked meat were inoculated alone (monocultured) or co-inoculated (co-cultured) onto cooked ham slices. The growth characteristics, lag phase duration (LPD, h), growth rate (GR, log₁₀ cfu/h), and maximum population density (MPD, log₁₀ cfu/g), of L. monocytogenes and the native microflora in vacuum-packed ham slices stored at 4, 6, 8, 10, and 12 °C for up to 5 weeks were determined. At 4-12 °C, the LPDs of co-cultured L. monocytogenes were not significantly different from those of monocultured L. monocytogenes in ham, indicating the LPDs of L. monocytogenes at 4-12 °C were not influenced by the presence of the native microflora. At 4-8 °C, the GRs of co-cultured L. monocytogenes (0.0114-0.0130 log₁₀ cfu/h) were statistically but marginally lower than those of monocultured L. monocytogenes (0.0132-0.0145 log₁₀ cfu/h), indicating the GRs of L. monocytogenes at 4-8 °C were reduced by the presence of the native microflora. The GRs of L. monocytogenes were reduced by 8-7% with the presence of the native microflora at 4-8 °C, whereas there was less influence of the native microflora on the GRs of L. monocytogenes at 10 and 12 °C. The MPDs of L. monocytogenes at 4-8 °C were also reduced by the presence of the native microflora. Data from this study provide additional information regarding the growth suppression of L. monocytogenes by the native microflora for assessing the survival and growth of L. monocytogenes in ready-to-eat meat products.     

Antimicrobial activity of Satureja montana L. essential oil against Clostridium perfringens type A inoculated in mortadella-type sausages formulated with different levels of sodium nitrite

This research evaluated the antimicrobial effect of the winter savory (Satureja montana L.) essential oil (EO) against Clostridium perfringens type A (ATCC 3624) inoculated in mortadella-type sausages formulated with different levels of sodium nitrite (NaNO₂: 0 ppm, 100 ppm and 200 ppm) in addition to EO at concentrations of 0.0%, 0.78%, 1.56% and 3.125% stored at 25 °C for 30 days. The EO extracted by hydrodistillation and analyzed by gas chromatography-mass spectrometry (CG-MS) was tested in vitro using an agar well diffusion method for determination of minimum inhibitory concentration (MIC) on C. perfringens. According to compositional analysis of the winter savory EO, 26 chemical compounds were identified, and the major constituents were thymol (28.99%), p-cymene (12.00%), linalool (11.00%) and carvacrol (10.71%). The results obtained showed that EO applied at a concentration of 1.56%, which was defined as the MIC, exhibited antimicrobial activity against C. perfringens in the in vitro assays, and the transmission electron microscopy (TEM) revealed structural damage and cell lysis of C. perfringens caused by EO treatment. A synergistic effect between NaNO₂ and EO was observed. In mortadella-type sausages formulated with 100 ppm of NaNO₂ and EO at all concentrations tested, the population of target microorganisms was reduced (p ≤ 0.05) compared to control samples during all storage period. This data suggests the potential combined use of savory EO and minimal amounts of the synthetic additive, NaNO₂ to control C. perfringens in mortadella, which goes according to current market trends, where consumers are requesting natural products.     

Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100–200 MPa, 7 min) and elevated temperature (80 °C, 10 min); spore germination at high temperatures (55, 60 or 65 °C); and inactivation of germinated spores with elevated temperatures (80 and 90 °C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 °C, 10 min). Low pressures (100–200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 °C, 10 min), and germinated at temperatures lethal for vegetative cells (≥55 °C) when incubated for 60 min with a mixture of l-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (∼4 decimal reduction) in meat by elevated temperatures (80–90 °C for 20 min) required a long germination period (55 °C for 60 min). However, similar inactivation level was reached with shorter germination period (55 °C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 °C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 °C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 °C in about 20 min and further incubation at 55 °C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 °C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.     

Curing properties of sodium nitrite in restructured goat meat (chevon) jerky

Known curing impacts on goat meat (chevon) is limited due to the low production and consumption of chevon products in the United States. This study, therefore, assessed sodium nitrite influences on the quality parameters of restructured chevon jerky and its stability. Inclusion of NaNO₂ increased (p < 0.01) the redness of chevon jerky (14.2 versus 8.17); however, the redness was decreased (p < 0.01) over a 30 d storage period. The texture properties and microbial counts of jerky were not influenced by NaNO₂. However, the total microbial counts increased (1.84 to 6.00 ± 0.468 log CFU/g; p < 0.01) with storage time in chevon jerky whether or not nitrite was included. Inclusion of NaNO₂ decreased (p < 0.05) thiobarbituric acid reactive substances values (4.26 versus 4.81 mg MDA/kg), which did not change during storage. Among 28 isolated fatty acids from chevon jerky, palmitic (C16:0), stearic (C18:0), oleic (C18:1n9), and linoleic (C18:2n6) acids were the major four fatty acids. Of the 21 positively identified volatile compounds, six terpenes (α-pinene, β-pinene, β-phellandrene, carene, limonene, and cubebene), octanone and nonanal were the most abundant compounds. Neither processing treatment nor storage time significantly influenced the concentration of individual fatty acids and volatile compounds. Cured jerky had higher (p < 0.05) sensory color and flavor scores compared to uncured jerky. Results indicated that inclusion of NaNO₂ might improve color and sensory properties, as well as control the lipid oxidation of chevon jerky. However, the reduction of lipid oxidation in jerky was not revealed in product fatty acid or volatile flavor compounds.     

Effects of high hydrostatic pressure and varying concentrations of sodium nitrite from traditional and vegetable-based sources on the growth of Listeria monocytogenes on ready-to-eat (RTE) sliced ham

The objective of this study was to determine the effect the source of added nitrite and high hydrostatic pressure (HHP) had on the growth of Listeria monocytogenes on ready-to-eat (RTE) sliced ham. Use of 600 MPa HHP for 3 min resulted in an immediate 3.9–4.3 log CFU/g reduction in L. monocytogenes numbers, while use of 400 MPa HHP (3 min) provided less than 1 log CFU/g reduction. With the 600 MPa HHP treatment, sliced ham with a conventional concentration of sodium nitrite (200 ppm) was not different in L. monocytogenes growth from use with 50 or 100 ppm of sodium nitrite in pre-converted celery powder. Instrumental color values as well as residual nitrite and residual nitrate concentrations for cured (sodium nitrite and nitrite from celery powder) and uncured ham formulations are discussed.     

Lack of growth of Listeria monocytogenes and Staphylococcus aureus in temperature abuse of E-beam treated ready-to-eat (RTE) cooked ham

The behaviour of Listeria monocytogenes and Staphylococcus aureus in vacuum-packed cooked ham slices treated with an electron beam and stored at 4, 7 and 10 °C was investigated. Cooked ham slices were inoculated with L. monocytogenes and S. aureus and electron beam treated at 2 and 3 kGy. After treatment, a long temperature-dependent death phase was observed, followed by growth at a slower rate than in untreated samples. Assuming a hypothetical load of 10 cells/g or cm² of L. monocytogenes and S. aureus as an original contamination in an industrial situation, an E-beam treatment of vacuum-packed cooked ham slices at 2 kGy guarantees the microbiological safety of the product along its shelf life, even if a noticeable temperature (10 °C) abuse occur during its storage period. Likewise, the E-beam treatment gave rise to a substantial increase of the RTE cooked ham shelf life off-sensory features associated to the spoilage only were detected in non-treated samples (controls) after 8 and 18 days of storage at 10 °C and 7 °C, respectively.     

Inactivation strategy for Clostridium perfringens spores adhered to food contact surfaces

The contamination of enterotoxigenic Clostridium perfringens spores on food contact surfaces posses a serious concern to food industry due to their high resistance to various preservation methods typically applied to control foodborne pathogens. In this study, we aimed to develop an strategy to inactivate C. perfringens spores on stainless steel (SS) surfaces by inducing spore germination and killing of germinated spores with commonly used disinfectants. The mixture of l-Asparagine and KCl (AK) induced maximum spore germination for all tested C. perfringens food poisoning (FP) and non-foodborne (NFB) isolates. Incubation temperature had a major impact on C. perfringens spore germination, with 40 °C induced higher germination than room temperature (RT) (20 ± 2 °C). In spore suspension, the implementation of AK-induced germination step prior to treatment with disinfectants significantly (p < 0.05) enhanced the inactivation of spores of FP strain SM101. However, under similar conditions, no significant spore inactivation was observed with NFB strain NB16. Interestingly, while the spores of FP isolates were able to germinate with AK upon their adhesion to SS chips, no significant germination was observed with spores of NFB isolates. Consequently, the incorporation of AK-induced germination step prior to decontamination of SS chips with disinfectants significantly (p < 0.05) inactivated the spores of FP isolates. Collectively, our current results showed that triggering spore germination considerably increased sporicidal activity of the commonly used disinfectants against C. perfringens FP spores attached to SS chips. These findings should help in developing an effective strategy to inactivate C. perfringens spores adhered to food contact surfaces.     

Survey of naturally and conventionally cured commercial frankfurters,ham, and bacon for physio-chemical characteristics that affect bacterial growth

Natural and organic food regulations preclude the use of sodium nitrite/nitrate and other antimicrobials for processed meat products. Consequently, processors have begun to use natural nitrate/nitrite sources, such as celery juice/powder, sea salt, and turbinado sugar, to manufacture natural and organic products with cured meat characteristics but without sodium nitrite. The objective of this study was to compare physio-chemical characteristics that affect Clostridium perfringens and Listeria monocytogenes growth in naturally cured and traditionally cured commercial frankfurters, hams, and bacon. Correlations of specific product characteristics to pathogen growth varied between products and pathogens, though water activity, salt concentration, and product composition (moisture, protein and fat) were common intrinsic factors correlated to pathogen growth across products. Other frequently correlated traits were related to curing reactions such as % cured pigment. Residual nitrite and nitrate were significantly correlated to C. perfringens growth but only for the ham products.     

Protective role of Lactobacillus fermentum R6 against Clostridium perfringens in vitro and in chicken breast meat under temperature abuse conditions

Six bacterial species were evaluated to determine their inhibitory effects on Clostridium perfringens in vitro (brain heart infusion broth) and in situ (chicken breast meat) under temperature abuse conditions (4 ± 1 °C for 12 h, followed by 7 h at 28 ± 1 °C and then 4 ± 1 °C for 53 h). During abusive storage, rapid growth of C. perfringens from vegetative cell and spore inocula was observed, exhibiting a 2.68–3.37 log CFU/mL (or g) increase in bacterial counts. In the presence of Pediococcus pentosaceus P1 or Lactobacillus fermentum R6, the counts of C. perfringens remained unchanged in the samples containing vegetative cells at the end of storage (P < 0.05); for those containing spores, the germination and outgrowth were also effectively inhibited, decreasing in bacterial counts of > 1.9 log CFU/mL (or g) compared to those of the control (P < 0.05). The pH of chicken meat was slightly declined by 0.09 in the presence of L. fermentum (P > 0.05), and the inhibitory effect against C. perfringens was ascribed to non-acid antimicrobial substances. These results indicate a potential solution for bio-protecting chicken meat from C. perfringens growth.Industrial relevanceClostridium perfringens is a common pathogen that contaminates meat and meat products, but the organism cannot multiply under cold chain conditions at 4 °C. However, it was reported that temperature abuses commonly occurred during the transportation, storage or retail display of the food chill chain. During the abusive storage, C. perfringens could grow rapidly, which may lead to food poisoning. It is a serious problem for food safety.In this study, Lactobacillus fermentum R6 was found to show effective inhibition on both the growth of C. perfringens vegetative cells and the germination and outgrowth of its spores in chicken meat (P < 0.05) under temperature abuse conditions, and also it had a minimal effect on the pH of the meat (P > 0.05). The results reveal a potential technology for bio-protecting chicken meat from C. perfringens growth.     

High pressure thermal processing for the inactivation of Clostridium perfringens spores in beef slurry

The spores of Clostridium perfringens can survive and grow in cooked/pasteurized meat, especially during the cooling of large portions. In this study, 600 MPa high pressure thermal processing (HPTP) at 75 °C for the inactivation of C. perfringens spores was compared with 75 °C thermal processing alone. The HPTP enhanced the inactivation of C. perfringens spores in beef slurry, resulting in 2.2 log reductions for HPTP vs. no reductions for thermal processing after 20 min. Then, the HPTP resistance of two C. perfringens spore strains in beef slurry at 600 MPa was compared and modeled, and the effect of temperature investigated. The NZRM 898 and NZRM 2621 exhibited similar resistance, and Weibull modeled well the log spore survivor curves. The spore inactivation increased when HPTP temperature was raised from 38 to 75 °C. The results confirm the advantage of high pressure technology to increase the thermal inactivation of C. perfringens spores in beef slurry.Industrial relevanceC. perfringens spores may cause food/meat poisoning as a result of improperly handled and prepared foods in industrial kitchens. Thermal processes at 100 °C or higher are generally carried out to ensure the elimination of these pathogenic spores. High pressure processing (HPP) is a food pasteurization technique which would help to maintain the sensorial and nutritional properties of food. Preservation of foods with HPP in conjunction with mild heat (HPTP) would enhance the spore inactivation compared to thermal processing alone at the same temperature, due to a known germination–inactivation mechanism. This technology, together with the application of Good Manufacturing Practices, including rapid cooling, is a good alternative to the traditional methods for producing safe processed meat and poultry products with enhanced sensory and nutritional quality.     

Technology-induced selection towards the spoilage microbiota of artisan-type cooked ham packed under modified atmosphere

The microbiota associated with a highly-perishable Belgian artisan-type cooked ham was analyzed through plating and (GTG)₅-fingerprinting of isolates throughout its processing chain. The raw tumbled meat was characterized by the presence of a versatile microbiota around 4.8 log(cfu g⁻¹), consisting of lactic acid bacteria, staphylococci, Brochothrix thermosphacta, Gram-negative bacteria, and yeasts. Pasteurisation of the ham logs reduced bacterial counts below 2 log(cfu g⁻¹) and subsequent manipulations selected for leuconostocs and carnobacteria. Also, B. thermosphacta and several Enterobacteriaceae were found at this stage. During storage in an intermediate high-care area for 2 days, a selection towards certain Enterobacteriaceae (Hafnia alvei, Enterobacter spp., and Pantoea agglomerans) and lactic acid bacteria (mainly vagococci and Streptococcus parauberis) was observed. B. thermosphacta, Leuconostoc carnosum and carnobacteria were also detected, but only after allowing bacterial outgrowth by incubating the meat logs at 7 °C for four weeks. After a mild post-pasteurisation process and subsequent handling, incubation of the meat logs at 7 °C for four weeks led to outgrowth of Enterobacteriaceae (mainly Enterobacter spp. and Serratia spp.). B. thermosphacta, and lactic acid bacteria (Enterococcus faecalis, Leuc. carnosum, and Carnobacterium maltaromaticum) were also found. After slicing and packaging under modified atmosphere, the microbiota of the refrigerated end-product consisted of leuconostocs, carnobacteria, and B. thermosphacta.     

Combined effect of high pressure and vinegar addition on the control of Clostridium perfringens and quality in nitrite-free emulsion-type sausage

We evaluated the combined effect of high pressure (HP) and vinegar addition on control of Clostridium perfringens and quality in emulsion-type pork sausages. Sausages were manufactured with different levels of commercial white distilled vinegar made with jasmine tea extract (0, 1, and 2%) and sodium nitrite (0.02%, control). The sausages except for sodium nitrite treatment were subjected to HP at 500 MPa (four cycles and each for 3 min). After storage, the combined treatment of HP and vinegar showed the lowest number of C. perfringens vegetative cells (4.8-log CFU/g reduction) among the all treatments. The combined treatment also inhibited the growth of C. perfringens spores for five weeks (stored at 4 °C for two weeks followed by at 20 °C for three weeks). Among all treatment combinations, the best pH, water-holding capacity and chewiness, were found with the HP-vinegar sausage. In addition, vinegar treatment inhibited the lipid oxidation of sausage throughout the storage. Use of HP and vinegar addition inhibited growth of C. perfringens without observed adverse effects on quality of the emulsion-type sausage.Industrial relevanceCurrently, the use of natural additives and novel processing technologies for replacing sodium nitrite in meat products is gaining attention owing to increase in consumer demand for nitrite-free and safe meat products. The study showed that the addition of 1% (w/v) of vinegar and pressure treatment at 500 MPa (four cycles and each for 3 min) can replace sodium nitrite to inhibit growth of C. perfringens in emulsion-type sausages.     

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.     

Oxidation in HiOx-packaged pork Longissimus muscle predisposes myofibrillar and sarcoplasmic proteins to N-nitrosamine formation in nitrite-curing solution

The effect of meat protein in situ oxidation on the formation of N-nitrosodiethylamine (NDEA) was investigated. Fresh minced pork was untreated (Con) or treated with 700 mg/kg α-tocopherol (Toc) or 300 mg/kg tea polyphenols (PPE), packaged in a HiOx atmosphere (78.8% O₂, 18.8% CO₂, 2.4% N₂), then stored at 2 ± 1 °C for up to 10 days. Crude myofibrillar (MP) or sarcoplasmic (SP) protein (20 mg/mL) extracted from stored meat was reacted with 43 μM sodium nitrite at 80 °C for 1 h. Lipid oxidation was totally inhibited in PPE pork but increased in Con and Toc samples after 10 days. There was significant protein oxidation (losses of sulfhydryls, formation of protein carbonyls) in both MP and SP in all samples during storage. However, the Con group suffered more extensive protein oxidation than Toc and PPE and produced more NDEA (P < 0.05), indicating that protein oxidation promoted nitrosation.     

Fluorescent in situ hybridization in combination with filter cultivation (FISHFC) method for specific detection and enumeration of viable Clostridium perfringens

To reduce time for enumeration of viable Clostridium perfringens, fluorescence in situ hybridization in combination with filter cultivation (FISHFC) was employed. The method utilized a CLP-180 probe, based on the 16S rRNA region of C. perfringens, and FISHFC fluorescence microscopy to detect C. perfringens, but not organisms from other species. Optimal cultivation requirements for micro-colony formation were TSC medium, anaerobic conditions, 37 °C, and incubation for 6 h. Under these conditions, micro-colony diameters reached 100 μm, a size sufficient for hybridization. Enumeration of C. perfringens using the CLP-180-aided FISHFC method was realized in 9 h as compared to 3–5 days required by the conventional plate count method. Moreover, viable C. perfringens counts of food samples from the two methods were not significantly different.     

Sodium lactate,sodium diacetate and pediocin: Effects and interactions on the thermal inactivation of Listeria monocytogenes on bologna

The effects and interactions of temperature (56.3–60 °C), sodium lactate (SL; 0–4.8%), sodium diacetate (SD; 0–0.25%) and pediocin (0–10,000 AU) on Listeria monocytogenes on bologna were studied and a predictive inactivation model was developed. Bologna was manufactured with different SL/SD concentrations in the formulation, dipped in pediocin solution and treated at different temperatures using combinations of parameters determined by central composite design. D-values were calculated and analyzed using second order response regression. Predicted D-values were also calculated. The observed D-values for L. monocytogenes on bologna ranged from 2.10 to 35.59 min. Temperature alone decreased predicted D-values from 99.02 min at 56.3 °C to 44.71 min at 60.0 °C. Adding SL decreased D-values (85.43–22.71 min) further; however, heat and SD combined was the most effective for reducing L. monocytogenes on bologna. An SD level of 0.25% at 58.2 °C had the overall lowest predicted D-value (15.95 min). Combination treatments increased or decreased D-values, depending on the temperature. Pediocin (2500 and 5000 AU) and heat decreased D-values, but exhibited a protective effect at higher concentrations (≥7500 AU). The results showed that interactions between additives in formulations can vary at different temperatures/concentrations, thereby affecting thermal inactivation of foodborne pathogens in meat products. Hence, food processors should modify food formulations carefully, and verify with adequate testing so that product safety is not compromised.     

Survival of Campylobacter jejuni on beef and pork under vacuum packaged and retail storage conditions: examination of the role of natural meat microflora on C. jejuni survival

The ability of Campylobacter jejuni ATCC 11168 to survive on beef and pork stored under chilled, vacuum packaged and retail display conditions were examined. In addition, the effect of natural microflora on commercial beef and pork on the survival of C. jejuni under these storage conditions was examined. When sterile cores of beef and pork were inoculated with ∼10⁵ to 10⁶ cfu cm⁻²C. jejuni, and were stored under aerobic or vacuum packaged conditions at −1.5 or 4 °C, its numbers dropped significantly and C. jejuni could not be enumerated by direct plating after 21 d of the 6 wks study. In contrast, survival of C. jejuni on commercial vacuum packaged beef and pork was significantly enhanced, resulting in only 1 log cfu cm⁻² reduction at the end of 6 wks. During 7 d of display in a retail case, numbers of C. jejuni dropped quickly, but could be enumerated by direct plating even after the 7 d. The presence of high numbers of inoculated C. jejuni on beef and pork had no significant effect on the natural microflora numbers compared to uninoculated controls when the meat was stored either in vacuum or in a retail display case. These results show that natural microflora on vacuum packaged meat afford enhanced survival of C. jejuni present on the surfaces of both beef and pork when stored at refrigeration temperatures. Hence, strict hygienic practices or the implementation of decontamination technologies are recommended to ensure safety of meat with respect to this pathogen.     

Effects of curing additives on the control ofListeria monocytogenesby lactocin 705 in meat slurry

Meat slurry inoculated withListeria monocytogenes(4.00 cfu g⁻¹) was mixed with different levels of curing additives and their influence on the inhibitory effect of lactocin 705 (17,000 AU ml⁻¹) was evaluated at 20°C. Inhibition ofL. monocytogeneswas 1.90 and 1.00 log less in meat slurry with 5 and 7% NaCl than in meat slurry without added sodium chloride. When nitrite and bacteriocin were added together, less nitrite (200 μg g⁻¹) was required to obtain the sameListeriapopulation (3.00 log cfu g⁻¹) as when 800 μg g⁻¹NaNO₂was used. However, when compared with lactocin 705 alone, lessListeriainhibition was observed showing also a protective effect of NaNO₂. When ascorbic acid and alginate meat binder were assayed in the presence of the bacteriocin, the inhibition ofL. monocytogeneswas less effective, but when sodium lactate (2%) was added to the meat slurry, almost no protective effect was observed. These results indicated that the use of lactocin 705 to controlL. monocytogeneswas less effective in the presence of curing ingredients.