Application of an active alginate coating to control the growth of Listeria monocytogenes on poached and deli turkey products

The relatively high prevalence of Listeria monocytogenes in ready-to-eat (RTE) turkey products is of great concern. The overall objective of this study was to develop antimicrobial edible coating formulations to effectively control the growth of this pathogen. The antimicrobials studied were nisin (500 IU/g), Novagard CB 1 (0.25%), Guardian NR100 (500 ppm), sodium lactate (SL, 2.4%), sodium diacetate (SD, 0.25%), and potassium sorbate (PS, 0.3%). These were incorporated alone or in binary combinations into five edible coatings: alginate, κ-carrageenan, pectin, xanthan gum, and starch. The coatings were applied onto the surface of home-style poached and processed deli turkey discs inoculated with ~ 3 log CFU/g of L. monocytogenes. The turkey samples were then stored at 22 °C for 7 days. For poached and processed deli turkey, the coatings were found to be equally effective, with pectin being slightly less effective than the others. The most effective poached turkey treatments seemed to be SL (2.4%)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%), which yielded final populations of 3.0 and 4.9 log CFU/g respectively compared to the control which was 7.9 log CFU/g. For processed deli turkey, the most effective antimicrobial treatments seemed to be Nisin (500 IU/g)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%) with final populations of 1.5 and 1.7 log CFU/g respectively compared to the control which was 6.5 log CFU/g. In the second phase of the study, home-style poached and store-purchased roasted (deli) turkey inoculated with the pathogen at a level of ~ 3 log CFU/g were coated with alginate incorporating selected antimicrobial combinations and stored for 8 weeks at 4 °C. Alginate coatings supplemented with SL (2.4%)/PS (0.3%) delayed the growth of L. monocytogenes with final counts reaching 4.3 log CFU/g (home-style poached turkey) and 6.5 log CFU/g (roasted deli turkey) respectively while the counts in their untreated counterparts were significantly higher (P < 0.05) reaching 9.9 and 7.9 log CFU/g, respectively. This study therefore demonstrates the effectiveness of using alginate-based antimicrobial coatings to enhance the microbiological safety and quality of RTE poultry products during chilled storage.     

Efficacy of bacteriophage LISTEXP100 combined with chemical antimicrobials in reducing Listeria monocytogenes in cooked turkey and roast beef

The aim of this study was to verify the effectiveness of the commercially available anti-Listeria phage preparation LISTEX^™P100 in reducing Listeria monocytogenes on ready-to-eat (RTE) roast beef and cooked turkey in the presence or absence of the chemical antimicrobials potassium lactate (PL) and sodium diacetate (SD). Sliced RTE meat cores at 4 and 10 °C were inoculated with cold-adapted L. monocytogenes to result in a surface contamination level of 10³ CFU/cm². LISTEX^TMP100 was applied at 10⁷ PFU/cm² and samples taken at regular time intervals during the RTE product's shelf life to enumerate viable L. monocytogenes. LISTEX^™P100 was effective during incubation at 4 °C with initial reductions of L. monocytogenes of 2.1 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef without chemical antimicrobials (there was no significant difference to the initial L. monocytogenes reductions in the presence of LISTEX^TMP100 for cooked turkey containing PL and roast beef containing SD-PL). In the samples containing no chemical antimicrobials, the presence of phage resulted in lower L. monocytogenes numbers, relative to the untreated control, of about 2 log CFU/cm² over a 28-day storage period at 4 °C. An initial L. monocytogenes cell reduction of 1.5 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef containing no chemical antimicrobials was achieved by the phage at 10 °C (abusive temperature). At this temperature, the L. monocytogenes cell numbers of samples treated with LISTEX™ P100 remained below those of the untreated control only during the first 14 days of the experiment for roast beef samples with and without antimicrobials. On day 28, the L. monocytogenes numbers on samples containing chemical antimicrobials and treated with LISTEX^TMP100 stored at 4 and 10 °C were 4.5 log₁₀ CFU/cm² and 7.5 log₁₀ CFU/cm², respectively, for cooked turkey, and 1.2 log₁₀ CFU/cm² and 7.2 log₁₀ CFU/cm², respectively, for roast beef. In both cooked turkey samples with and without chemical antimicrobials stored at 10 °C, the phage-treated samples had significantly lower numbers of L. monocytogenes when compared to the untreated controls throughout the 28-day storage period (P < 0.0001). For roast beef and cooked turkey containing chemical antimicrobials treated with LISTEX^TMP100 and stored at 4 °C, no more than a 2 log CFU/cm² increase of L. monocytogenes was observed throughout the stated shelf life of the product. This study shows that LISTEX^™P100 causes an initial reduction of L. monocytogenes numbers and can serve as an additional hurdle to enhance the safety of RTE meats when used in combination with chemical antimicrobials.     

Control of Growth of L. monocytogenes in Fresh Salmon using Microgard and Nisin

Pathogens like Listeria monocytogenes in fresh, or even in cold smoked salmon, have become a major public health concern for the salmon processing industry and government agencies. The effect of bacteriocin solutions (Microgard^™ and Nisin) on reducing total microbial counts, inhibiting Listeria monocytogenes, and prolonging the shelf-life was evaluated. Listeria monocytogenes was inoculated onto chilled and on frozen and thawed salmon samples. The combination of Nisin and Microgard reduced the total aerobic bacteria populations of fresh chilled salmon by 2 log (P<0.05) and increased its shelf-life, at 6 °C, by 3-4 d, as compared with the control. The above bacteriocin combination also reduced the growth of inoculated Listeria monocytogenes in frozen-thawed salmon and increased its shelf-life from 5 to 10 d at 6 °C. The bacteriocin treatment did not affect surface pH values or color of the fish.     

Antimicrobial activity of lactic acid bacteria against Listeria monocytogenes on frankfurters formulated with and without lactate/diacetate

Contamination by Listeria monocytogenes has been a constant public health threat for the ready-to-eat (RTE) meat industry due to the potential for high mortalities from listeriosis. Lactic acid bacteria (LAB) have shown protective action against various pathogenic bacteria. The aim of this study was to evaluate the antilisterial activity of a combination of three LAB strains (Lactiguard®) on L. monocytogenes. The combination of the LAB was inhibitory to L. monocytogenes inoculated onto frankfurters not containing lactate/diacetate after 8 weeks of refrigerated storage (0.6 log reduction compared to L. monocytogenes only control), and when a cell free extract (CFS) of the LAB was added with LAB even more inhibition was obtained (1.2 log reduction compared with L. monocytogenes only). In frankfurters containing lactate/diacetate the LAB and the LAB plus CFS were more effective in reducing growth of L. monocytogenes after 8 weeks of refrigerated storage (2 and 3.3 log reductions respectively).     

Antimicrobial activity of lactic acid bacteria against Listeria monocytogenes on frankfurters formulated with and without lactate/diacetate

Contamination by Listeria monocytogenes has been a constant public health threat for the ready-to-eat (RTE) meat industry due to the potential for high mortalities from listeriosis. Lactic acid bacteria (LAB) have shown protective action against various pathogenic bacteria. The aim of this study was to evaluate the antilisterial activity of a combination of three LAB strains (Lactiguard®) on L. monocytogenes. The combination of the LAB was inhibitory to L. monocytogenes inoculated onto frankfurters not containing lactate/diacetate after 8 weeks of refrigerated storage (0.6 log reduction compared to L. monocytogenes only control), and when a cell free extract (CFS) of the LAB was added with LAB even more inhibition was obtained (1.2 log reduction compared with L. monocytogenes only). In frankfurters containing lactate/diacetate the LAB and the LAB plus CFS were more effective in reducing growth of L. monocytogenes after 8 weeks of refrigerated storage (2 and 3.3 log reductions respectively).     

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.     

Effects of Antimicrobial Coatings and Cryogenic Freezing on Survival and Growth of Listeria innocua on Frozen Ready‐to‐Eat Shrimp during Thawing

Foodborne pathogens such as Listeria monocytogenes could pose a health risk on frozen ready‐to‐eat (RTE) shrimp as the pathogen could grow following thawing. In this study, antimicrobial‐coating treatments alone, or in combination with cryogenic freezing, were evaluated for their ability to inhibit the growth of Listeria innocua, a surrogate for L. monocytogenes, on RTE shrimp. Cooked RTE shrimp were inoculated with L. innocua at 3 population levels and treated with coating solutions consisting of chitosan, allyl isothiocyanate (AIT), or lauric arginate ester (LAE). The treated shrimp were then stored at –18 °C for 6 d before being thawed at 4, 10, or 22 °C for either 24 or 48 h. Results revealed that antimicrobial coatings achieved approximately 5.5 to 1 log CFU/g reduction of L. innocua on RTE shrimp after the treatments, depending on the inoculated population levels. The coating‐treated shrimp samples had significantly (P < 0.05) less L. innocua than controls at each thawing temperature and time. Cryogenic freezing in combination with coating treatments did not achieve synergistic effects against L. innocua. Antimicrobial coatings can help to improve product safety by reducing Listeria on RTE shrimp.     

Growth of Listeria monocytogenes on a RTE-meat matrix enhances cell invasiveness to mouse J774A.1 macrophages

It remains unclear whether the growth of Listeria monocytogenes on a ready-to-eat (RTE) meat matrix has an impact on the bacterium's pathogenic abilities. In this study, we investigated the impact of environments on virulence by growing L. monocytogenes (F2365 strain) on brain heart infusion agar (BHI), tryptic soy agar (TSA), and RTE turkey meat matrices. Bacteria cultured from these media were harvested and used to infect mouse macrophage cell line J774A.1 with different MOIs to examine their invasion ability. At MOI = 10 and 50, the numbers of bacteria recovered from cells infected with turkey-meat-grown Listeria were significantly higher than those from the two nutrient-rich growth media. Additionally, MOI played a role in determining L. monocytogenes recovery rates, since significant differences were found amongst all three groups at low MOI, while no significant differences were found between BHI and TSA groups at high MOI. These results indicate that environmental changes affect the ability of L. monocytogenes to invade and survive intracellularly while grown on RTE-meat matrix.     

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.     

Superchilled,chilled and frozen storage of Atlantic mackerel (Scomber scombrus) fillets – changes in texture,drip loss,protein solubility and oxidation

Changes in quality characteristics in relation to protease activity and protein oxidation in chilled, superchilled and frozen mackerel fillets during storage were studied. The solubility of sarcoplasmic proteins was quite stable in mackerel samples for all storage experiments, whereas the solubility of myofibrillar proteins decreased in both superchilled and frozen samples. A significant correlation (r = 0.983, P < 0.05) between the increased activity of cathepsin B+L in chilled fillets and softening of the fish flesh during storage was revealed. Contrary with chilled samples, the texture of superchilled mackerel fillets became tougher along the storage period, which can be explained by a higher rate of myofibrillar oxidation (r = 0.940, P < 0.05). The hardness and drip loss decreased slightly at the end of frozen storage. Superchilling preserved the quality of mackerel fillets with the least side effects in relation to protein solubility, drip loss and softening of the fish tissue as compared to chilled and frozen storage.     

Reductionin Listeria monocytogenes,Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

Increased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P < 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.     

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.     

Fate of Listeria monocytogenes during freezing,thawing and home storage of frankfurters

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 °C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm²) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 °C for 6 or 30 d and then frozen (−15 °C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 °C, 24 h), on a countertop (23 ± 2 °C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 °C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 °C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 °C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm², respectively), while freezing reduced counts by <1.0 log CFU/cm². Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm²), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm² at d-7 of aerobic storage, and reached 5.6 log CFU/cm² at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.     

Effect of edible coatings on enzymes,cell-membrane integrity,and cell-wall constituents in relation to brittleness and firmness of Huanghua pears (Pyrus pyrifolia Nakai,cv. Huanghua) during storage

To investigate the effects of edible coatings, such as shellac and Semperfresh™ (sucrose-polyester based coating) on the brittleness and firmness of Huanghua pears (Pyrus pyrifolia Nakai, cv. Huanghua), the changes in the cell-membrane permeability and cell-wall constituents, such as total pectin (TP), Na₂CO₃-soluble pectin (NSP), CDTA-soluble pectin (CSP), water-soluble pectin (WSP), hemicellulose and cellulose were periodically measured, for up to 60 days of cold storage (4 °C) after harvesting. The activities of peroxidase (POD), pectinesterase (PE), polygalacturonase (PG), and cellulose were also assayed. The data suggested that high POD activity and low activity of cell-wall-degrading enzymes, such as PE, PG, and cellulase in the coated pears were associated with a high integrity of the cell membrane and few changes in the cell-wall constituents, which contributed to high levels of brittleness and firmness in the pears during storage; further, the shellac coating provided a better effect than Semperfresh coating.     

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

The effects and interactions of temperature (56.3-60 °C), sodium lactate (SL; 0-4.8%), sodium diacetate (SDA; 0-2.5%), and pediocin (0-10,000 AU) on starved Listeria monocytogenes (10⁷ CFU/g) on bologna were investigated. Bologna slices containing SL and SDA in the formulation were dipped in pediocin, surface inoculated, and treated at various temperatures using combinations of parameters determined by central composite design. D-values were calculated. The observed D-values ranged from 2.8 min at 60 °C to 24.61 min at 56.3 °C. Injury ranged from 9.1 to 76% under various conditions. The observed D-values were analyzed using second order response surface regression for temperature, SL, SDA, and pediocin, and a predictive model was developed. Predicted D-values were calculated and ranged from 3.7 to 19 min for various combinations of parameters. Temperature alone reduced the predicted D-values from 33.96 min at 56.3 °C to 11.51 min at 60 °C. Addition of SL showed a protective effect. Other combination treatments either reduced or increased D-values depending on temperature. The combination of SL and SDA was effective at lower temperatures, however, higher levels of SDA at higher temperatures made the organism more heat resistant. Pediocin (up to 5000 AU) with increasing temperature and SDA reduced D-values. Depending on temperature and concentration, the interactions between various additives can affect thermal inactivation of L. monocytogenes on bologna. Starvation rendered L. monocytogenes more susceptible to heat and additives.     

Listeria monocytogenes and ready-to-eat seafood in Spain: Study of prevalence and temperatures at retail

The aim of this study was to obtain data from refrigerated ready-to-eat seafood products at retail in Spain (young eels, crabstick and smoked salmon), regarding prevalence and levels of Listeria monocytogenes, storage temperatures and the impact of transport conditions (type of bag) on the temperature of the product. The one-year surveillance period was carried out according to the EC Regulation No. 2073/2005, taking 5 units/batch and analyzing 250 samples following ISO 11290-1/A1 and ISO 11290-2/A methodologies. Low prevalence of L. monocytogenes was observed in surimi products, while 4.8% of smoked salmon samples were positive for Listeria with low levels (<10 cfu/g) and uneven pathogen distribution. A single company was responsible for 80% of the positive lots. All purchased products showed values higher than 4 °C at retail and an average increase of 2.5 °C or up to 6.2 °C was recorded when isothermal or plastic shopping bags were used for transport, respectively. To avoid noncompliance of the Food Safety Objective for L. monocytogenes in seafood RTE products more efforts from all stakeholders are needed, with special attention so as to improve control and maintenance of refrigerators at retail and to enhance consumer education regarding food safety practices.     

Anti-Listeria monocytogenes activity of enterocins microencapsulated by ionic gelation

The encapsulation of enterocins synthesized by Enterococcus faecium CRL1385 through ionic gelation with calcium ions was analyzed. Different enterocins samples were lyophilised and encapsulated using low-methoxyl pectin as the coating material. Lipids present in milk butter were also added to control the release of antimicrobial peptides from the capsules. The morphology of fresh and freeze-dried capsules was examined using light microscopy and scanning electron microscopy, respectively. Antimicrobial activity of encapsulated bacteriocins was assessed against Listeria monocytogenes 01/155 using the agar diffusion technique and direct contact in microplates. The capsules with higher lipid content showed a more spherical and uniform shape. Pathogen inhibition was observed for capsules prepared with different bacteriocin solutions both on solid (halo diameter = 8.5–13.5 mm) and in an aqueous medium (ca. 2 log orders decline in L. monocytogenes viability). The outcomes suggest that bacteriocin encapsulation through ionic gelation can be a potential alternative for the application of these antimicrobial peptides as biopreservatives in food.     

Use of octanoic acid as a postlethality treatment to reduce Listeria monocytogenes on ready-to-eat meat and poultry products

The antilisterial efficacy and organoleptic impact of an octanoic acid (OA)-based treatment for ready-to-eat (RTE) meat and poultry products were investigated. Whole-muscle and comminuted RTE products were inoculated with a five-strain mixture of Listeria monocytogenes. The OA treatments were applied to the surface of RTE products by dispensing a specific volume of solution directly into the final package prior to vacuum sealing. Once sealed, the vacuum-packaged RTE products containing OA were immersed in water heated to 93.3 degrees C (200 degrees F) for 2 s to effect adequate film shrinkage. Extending the time at which the packaged, treated RTE products were exposed to water heated to 93.3 degrees C was also evaluated with a commercial cascading shrink tunnel fitted with a modified drip pan. Once treated, RTE products were examined for survivor populations of L. monocytogenes after 24 h of storage at 5 degrees C. Sensory evaluation was conducted with a 60-member trained panel on 11 uninoculated, treated RTE products. The OA treatment of RTE products reduced L. monocytogenes numbers to between 0.85 log CFU per sample (oil-browned turkey) and 2.89 log CFU per sample (cured ham) when compared with controls. The antilisterial activity of OA was improved by increasing the duration of the heat shrink exposure. Specifically, reductions of L. monocytogenes ranged from 1.46 log CFU per sample (oil-browned turkey) to 3.34 log CFU per sample (cured ham). Results from the sensory evaluation demonstrated that 10 of the 11 treated RTE products were not perceived as different (P < or = 0.05) from the untreated controls. Panelists detected reduced (P < or = 0.05) smoke flavor intensity with treated mesquite turkey, although the treated product was viewed as acceptable. Results demonstrate the effectiveness of OA as a postlethality treatment meeting U.S. Food Safety and Inspection Service regulatory guidelines for RTE meat and poultry products with minimal impact on sensory quality.     

Effect of different activated coatings containing enterocin AS-48 against Listeria monocytogenes on apple cubes

Enterocin AS-48 is a circular bacteriocin with strong anti-Listeria activity. The purpose of the present study was to evaluate the effect of the bacteriocin incorporated into different coating solutions on a cocktail of five L. monocytogenes strains previously inoculated on apple cubes. Coating solutions were made with chitosan, caseinate, alginate, k-carrageenate, xanthan gum, pectin, starch, carboxymethyl cellulose or methyl cellulose. Coatings were applied singly or combined with enterocin AS-48 at 20 or 40 μg/ml. Samples were stored at 4 °C for 7 days. The single application of coatings had almost no effect (as in alginate and methyl cellulose) or had a low effect on Listeria viability (< 2.0 log cycles), with the exception of chitosan coating which showed a strong anti-Listeria activity (up to 3.7 log cycles at day 7). Coatings dosed with 20-μg/ml enterocin AS-48 reduced viable Listeria counts gradually during storage in most cases, achieving significant reductions (p < 0.05) of 1.0 to 1.9 log cycles after 7 days for k-carrageenate, xanthan gum, pectin, starch, carboxymethyl cellulose and methyl cellulose compared to the single coating. At 40 μg/ml, enterocin AS-48 significantly reduced viable counts (p < 0.05) for most coatings (by 1.4 to 3.3 log cycles, depending on the coating) compared with coatings without bacteriocin (except for chitosan). Chitosan, pectin, xanthan gum and carboxymethyl cellulose coatings, supplemented or not with 40 μg/ml AS-48 were further investigated in combination with 20 mM EDTA or with 2.0% sodium lactate. The single addition of sodium lactate showed the greatest effects at day 7, where it reduced viable counts significantly (p < 0.05) by 1.1 to 2.2 log cycles compared to the single coatings (except for chitosan), whereas the combination of sodium lactate and AS-48 reduced viable counts below detection levels also at day 7 for all coatings. The combination of EDTA and AS-48 was much more effective, reducing Listeria counts below detection levels from day 1 for most of the coatings tested. The combination of EDTA and AS-48 was also the most effective at time 0, achieving reductions of viable counts between 2.0 and 2.7 log cycles depending on the coating immediately after treatment compared with single coatings.Industrial relevanceResults from the present study suggest the potential of edible coatings containing enterocin AS-48 and EDTA for inactivation of L. monocytogenes on apple surfaces. Since edible coatings are widely used on fruit surfaces, coatings activated with enterocin AS-48 and EDTA could find application as a hurdle against L. monocytogenes in fresh-cut apple pieces.     

The probability of growth of Listeria monocytogenes in cooked salmon and tryptic soy broth as affected by salt,smoke compound,and storage temperature

The objectives of this study were to examine and model the probability of growth of Listeria monocytogenes in cooked salmon containing salt and smoke (phenol) compound and stored at various temperatures. A growth probability model was developed, and the model was compared to a model developed from tryptic soy broth (TSB) to assess the possibility of using TSB as a substitute for salmon. A 6-strain mixture of L. monocytogenes was inoculated into minced cooked salmon and TSB containing 0–10% NaCl and 0–34 ppm phenol to levels of 10^2–3 cfu/g, and the samples were vacuum-packed and stored at 0-–25 °C for up to 42 days. A total 32 treatments, each with 16 samples, selected by central composite designs were tested. A logistic regression was used to model the probability of growth of L. monocytogenes as a function of concentrations of salt and phenol, and storage temperature. Resulted models showed that the probabilities of growth of L. monocytogenes in both salmon and TSB decreased when the salt and/or phenol concentrations increased, and at lower storage temperatures. In general, the growth probabilities of L. monocytogenes were affected more profoundly by salt and storage temperature than by phenol. The growth probabilities of L. monocytogenes estimated by the TSB model were higher than those by the salmon model at the same salt/phenol concentrations and storage temperatures. The growth probabilities predicted by the salmon and TSB models were comparable at higher storage temperatures, indicating the potential use of TSB as a model system to substitute salmon in studying the growth behavior of L. monocytogenes may only be suitable when the temperatures of interest are in higher storage temperatures (e.g., >12 °C). The model for salmon demonstrated the effects of salt, phenol, and storage temperature and their interactions on the growth probabilities of L. monocytogenes, and may be used to determine the growth probability of L. monocytogenes in smoked seafood.