Listeria monocytogenes Inhibition by Whey Protein Films and Coatings Incorporating the Lactoperoxidase System

Antimicrobial effects of whey protein isolate (WPI) films and coatings incorporating the lactoperoxidase system (LPOS) against Listeria monocytogenes were studied by turbidity, plate counting, disc‐covering, and disc‐surface‐spreading tests using various growth media. Survival of L. monocytogenes applied to smoked salmon before or after the coating was monitored immediately after application and during storage at 4 °C and 10 °C for up to 35 d. Tensile properties (elastic modulus [EM], tensile strength [TS], elongation [E]), oxygen permeability (OP), and color (Hunter L, a, b) of WPI films, with and without LPOS, were also compared. LPOS inhibited L. monocytogenes in broth and on agar media. WPI films incorporating 29 mg of LPOS per gram of film (dry basis) inhibited 4.2 log colony‐forming units (CFU)/cm² of L. monocytogenes inoculated on agar media. WPI coatings prepared with LPOS at 0.7% (w/w) in a coating solution (40 mg LPOS/g coating [dry basis]) initially reduced >3 and 1 log CFU/g of L. monocytogenes and total aerobic microorganisms in smoked salmon, respectively. The WPI coatings incorporating LPOS prevented the growth of L. monocytogenes in smoked salmon at 4 °C and 10 °C for 35 d and 14 d, respectively. The tensile properties, oxygen permeability, and color of WPI films were not significantly changed by incorporation of LPOS (P >0.05).     

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.     

Listeria monocytogenes in genussfertigen Lebensmitteln: eine Auswertung der amtlichen Untersuchungen in der Schweiz der Jahre 2006–2008

In the years 2006–2008, 13.978 ready-to-eat foodstuffs were tested by official laboratories of food control in Switzerland for compliance with legal limits for Listeria monocytogenes. Totally, the pathogen could be detected in 67 foods (0,5 % of all samples). Most frequently, raw meat cured sausages (proportion of positive samples 3,9 %) were contaminated followed by smoked fishes (1,4 %) and semi-hard cheeses (1,1 %). For soft cheese, a rather low contamination frequency of 0,3 % was shown. Quantification of L. monocytogenes was possible in 18 ready-to-eat foods from the market and six out of them showed high counts of >1.000 CFU per gram. Concerned were a sandwich with smoked salmon and other components (250.000 CFU/g), smoked salmon (180.000 CFU/g), smoked trout (13.000 CFU/g), semi-hard cheese (9.200 CFU/g) and salami (5.500 and 1.850 CFU/g). In connection with cases of listeriosis, the highest measured count (5 × 10⁷ CFU/ml) was found in liquid cream of a private household where it was probably contaminated and not adequately stored. Surprisingly, in 931 desserts and confectioneries, in 384 ice-creams, in 3.567 pre-cooked foods and in 806 samples of raw fruits or vegetables, L. monocytogenes was never isolated and in 720 delicatessen salads only once (Celery salad with <100 CFU/g). The evaluation of a high number of laboratory data allowed identifying the current focal points of risk, an information which is important for a risk-based design of future control activities.     

Reduction of Listeria monocytogenes on frankfurters treated with lactic acid solutions of various temperatures

United States regulations require ready-to-eat meat and poultry processors to control Listeria monocytogenes using interventions which may include antimicrobials that reduce post-processing contamination by at least 1 log-cycle; if the treatment achieves ≥2 log reductions, the plant is subject to less frequent microbial testing. Lactic acid (LA) may be useful as a post-lethality intervention and its antimicrobial properties may increase with temperature of application. The aim of this study was to evaluate the effect of LA solution concentration and temperature on L. monocytogenes counts of inoculated frankfurters and to identify parameters (concentration, temperature, and time) that achieve 1 and 2 log-unit immediate reductions. Frankfurters were surface-inoculated with a 10-strain mixture of L. monocytogenes (4.4 ± 0.1 log CFU/cm²) and then immersed in distilled water or LA solutions (0–3%) of 4, 25, 40, or 55 °C for 0–120 s. A regression equation for L. monocytogenes reduction included significant (P < 0.05) effects by the terms of concentration, time, temperature, and the interaction of concentration and temperature; other tested parameters (other interactions, quadratic and cubic terms), within the experimental range examined, did not affect (P ≥ 0.05) the extent of reduction. Results indicated that the effectiveness of LA against L. monocytogenes, in addition to concentration, increased with solution temperature (in the range of 0.6–2.8 log CFU/cm²). The developed equation may allow processors to vary conditions of treatment with LA to achieve a 1 or 2 log-unit reduction of the pathogen and comply with United States regulations.     

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.     

A bacteriocin-like substance produced from Lactobacillus pentosus 39 is a natural antagonist for the control of Aeromonas hydrophila and Listeria monocytogenes in fresh salmon fillets

We studied the ability of Lactobacillus pentosus 39, a BLS (Bacteriocin-like substance)-producing strain, to control the growth of Aeromonas hydrophila ATCC 14715 and Listeria monocytogenes ATCC 19117 artificially added to fresh salmon fillets at refrigeration temperatures and under simulated cold-chain break conditions.At refrigeration temperatures, Lb. pentosus 39 protective culture and its putative bacteriocin significantly reduced A. hydrophila counts compared with the control (2.1 and 1.4 log CFU/g reductions, respectively). Similar behaviour was observed for L. monocytogenes (3.6 and 1.3 log CFU/g reductions, respectively).Under simulated cold-chain break conditions, an increase in temperature (30°C for 12h) produced an evident increase in the development of A. hydrophila, L. monocytogenes, but also of Lb. pentosus 39, with a consequent increase in BLS production. This condition resulted in a greater reduction of both pathogens compared with samples stored at 4°C throughout the experiment (2.8 log CFU/g reduction for A. hydrophila, 5.8 log CFU/g reduction for L. monocytogenes). In samples treated with the putative bacteriocin alone, a less marked decrease was observed.Our study demonstrates the capability of Lb. pentosus 39 to control the growth of psychrotrophic bacteria in an experimental seafood model system. A similar biopreservation technology could provide more prolonged shelf-life during storage of ready-to-eat seafood, ensuring safety, even under extreme conditions.     

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.     

Novel inactivation methods of Doenjang (fermented soybean paste) by high pressure and ohmic heating

The changes of the total cell number in doenjang (Korean traditional fermented soybean paste) by conventional conduction heating, high pressure non-thermal treatment, and ohmic heating were compared. A total of (10¹–10²) CFU/g cells were decreased by heating at (100–105) °C for 10 min. The inactivation rate was improved when heated to a temperature higher than 110 °C, but the taste, color of doenjang were severely changed. Inactivation by high pressure at (200–800) MPa was not achieved, because the total cell did not reach a reduction of 10¹ CFU/g. The total bacterial counts of 10³ CFU/g were decreased during ohmic heating at 15 V and 60 Hz for 10 min, and showed the most effective inactivation. Therefore, application of the ohmic heating in doenjang with high viscosity can kill target microorganisms related to quality deterioration, and rapid and uniform ohmic heating leads to reduction in sensory quality damage.     

Impact of chlorophyllin-chitosan coating and visible light on the microbial contamination,shelf life,nutritional and visual quality of strawberries

The aim of this study was to evaluate the antimicrobial efficiency of photoactivated chlorophyllin-chitosan conjugate (Chl–CHS) against main foodborne pathogens (L. monocytogenes, E. coli) and strawberry plant pathogen (Botrytis cinerea) in vitro and to assess the impact of Chl-CHS coating and visible light on the microbial contamination, spoilage, nutritional and visual quality of strawberries.Photoactivated Chl–CHS (0.001–0.1%, light λ = 405 nm, 38 J/cm²) reduced the viability of L. monocytogenes by 7 log, E. coli – by 4.5 log in vitro. Moreover, it inhibited B. cinerea growth by 60%. Comparative analysis of strawberry decontamination techniques indicated that soaking of strawberries in 200 ppm NaOCl diminished the population of yeasts/microfungi by 0.6 log, whereas coating of strawberries with Chl–CHS and illumination with visible light (dose 76 J/cm²) inactivated yeasts/microfungi on the fruits by 1.4 log. Moreover, Chl–CHS coating in the presence of light prolonged the shelf-life of strawberries by 3 days without any negative impact on the visual quality and color, saving weight losses, water content and antioxidant activity.In conclusion, photoactivated Chl–CHS coating possessed significant antimicrobial activity. Such coatings might serve for the future development of new generation light-active edible antimicrobial coatings, so important for effective preservation of traditional and organic strawberry production.     

The fate of Listeria monocytogenes during the manufacture of Camembert-type cheese: A comparison between raw milk and milk treated with high hydrostatic pressure

Camembert-type cheese was produced from: raw bovine milk; raw milk inoculated with 2 or 4 log CFU/ml Listeria monocytogenes; raw milk inoculated with L. monocytogenes and subsequently pressure-treated at 500 MPa for 10 min at 20 °C; or uninoculated raw milk pressure-treated under these conditions. Cheeses produced from both pressure-treated milk and untreated milk had the typical composition, appearance and aroma of Camembert. Curd and cheese made from inoculated, untreated milk contained large numbers of L. monocytogenes throughout production. An initial inoculum of 1.95 log CFU/ml in milk increased to 4.52 log CFU/g in the curd and remained at a high level during ripening, with 3.85 log CFU/g in the final cheese. Pressure treatment inactivated L. monocytogenes in the raw milk at both inoculum levels and the pathogen was not detected in any of the final cheeses produced from pressure-treated milk. Therefore high pressure may be useful to inactivate L. monocytogenes in raw milk that is to be used for the production of soft, mould-ripened cheese.

Industrial relevance

This paper demonstrates the potential of high pressure (HP) for treatment of raw milk to be used in the manufacture of soft cheeses. HP treatment significantly reduced the level of Listeria monocytogenes in the raw milk and so allowed the production of safer non-thermally processed camembert-like soft cheese.     

Growth potential of Listeria monocytogenes strains in mixed ready-to-eat salads

In this study, a microbiological challenge test in three artificially contaminated retail mixed mayonnaise-based ready-to-eat salads stored at refrigerator temperatures (3 °C and 7 °C) for 48 h was carried out. Shrimp-tomato salad, smoked ham salad and garlic cheese salad were separately contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes, Enterobacteriaceae, staphylococci and total plate count (CFU/g) was determined. Listeria monocytogenes growth potential in the salads was calculated and evaluated.A significant increase in total plate count and L. monocytogenes count throughout storage of all three investigated salads was found. Enterobacteriaceae levels were high at the beginning in all salads but significantly (p < 0.05) decreased throughout the experiment depending on the temperature.All investigated L. monocytogenes strains demonstrated growth at both temperatures but expressed different growth potential. Especially garlic cheese salad and smoked ham salad were able to support the growth of Listeria. Shrimp-tomato salad supported growth the least. The growth potential increased with the increasing temperature and exceeded 0.5 log₁₀ CFU/g in many cases. If the potential for growth is > 0.5 log₁₀ CFU/g, food products can potentially endanger human health. Reference strain (ATCC 7644) showed the least growth potential almost in all cases in comparison with strains isolated from frozen pollock loins and from thermally treated specialty sausage containing preservatives. To eliminate the occurrence of microbiological risks, the shelf-life of the studied salads was estimated.     

Effects of supercritical carbon dioxide treatment against generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7 in marinades and marinated pork

This study was conducted to evaluate the effects of supercritical carbon dioxide (SC-CO₂) treatment on soy sauce and hot-pepper paste marinades, as well as in marinated pork products, for the inhibition of generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7. SC-CO₂ was more effective at destroying foodborne pathogens when it was applied to the marinades than the marinated products. SC-CO₂ treatment at 14 MPa and 45 °C for 40 min resulted in a greater reduction in soy sauce (2.52–3.47 log CFU/cm²) than in hot-pepper paste marinade (2.12–2.72 log CFU/cm²). In the case of the marinated pork, when SC-CO₂ was applied at 14 MPa and 45 °C for 40 min, the reduction levels of L. monocytogenes were 2.49 and 1.92 log CFU/cm² in soy sauce and hot-pepper paste marinated pork, respectively. The results should be useful in the meat industry to help increase microbial safety and assure the microbial stability of marinades and marinated products.     

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.     

Reduction effect of the selected chemical and physical treatments to reduce L. monocytogenes biofilms formed on lettuce and cabbage

As people shift their attention away from unhealthy foods, healthy fresh produce has become popular. However, fresh produce has contributed to many outbreaks of Listeria monocytogenes, which can form a mature biofilm within 24 h. Recent control strategies have proved ineffective in ensuring safe food production. This study focuses on L. monocytogenes biofilms formed on lettuces and cabbages using a viable plate count method and field emission electron microscopy. We investigated the reduction efficacy of treatment with 200 parts per million (ppm) chlorine, 2% each of citric, lactic, and malic acids, 32 Hz ultrasonication (US), 390 mJ/cm² ultraviolet-C (UV-C), or 750 mJ/cm² cold oxygen plasma (COP) on L. monocytogenes biofilms. Following treatment, the quality of the vegetables was analyzed with standard procedures. UV-C and COP showed the best CFU reduction, regardless of the nature of the vegetable surface, while US failed to produce any significant reduction (P > 0.05). Furthermore, chemical treatments reduced count by < 1 log colony forming unit (CFU)/cm² on lettuces, whereas a > 2 log reduction was observed on cabbages. The effect of chemical treatment largely depended on the particular vegetable, while UV-C and COP achieved high reduction regardless of the vegetable, and had no effect on quality. We, therefore, speculate that UV-C and COP show promise in overcoming L. monocytogenes biofilms on food produce.     

Development of a chicken feather protein film containing clove oil and its application in smoked salmon packaging

Chicken feathers, a by-product of the poultry industry, were utilized as a film base material after extraction of chicken feather protein (CFP). Composite films of CFP and gelatin were prepared, and their mechanical properties were investigated. The tensile strength and elongation at break of the CFP/gelatin composite film significantly (p < 0.05) increased as the gelatin content in the film increased. As a cross-linking agent, 0.5% cinnamaldehyde further improved the film's mechanical properties. Incorporation of clove oil into the composite film resulted in strong inhibition zones against Escherichia coli O157:H7 and Listeria monocytogenes compared with the film without clove oil. Packaging smoked salmon with the composite film containing 1.5% clove oil resulted in a decrease in the populations of E. coli O157:H7 and L. monocytogenes by 1.41 and 1.34 log CFU/g, respectively, compared with the control during storage at 4 °C for 12 days. Furthermore, the peroxide value and thiobarbituric acid reactive substances value decreased by 28 and 36%, respectively, in the smoked salmon packaged with the composite film containing 1.5% clove oil compared with the control during storage. These results suggest that a CFP/gelatin composite film with 1.5% clove oil can be used as an active packaging material for smoked salmon.     

Effect of salt, smoke compound, and storage temperature on the growth of Listeria monocytogenes in simulated smoked salmon

Smoked salmon can be contaminated with Listeria monocytogenes. It is important to identify the factors that are capable of controlling the growth of L. monocytogenes in smoked salmon so that control measures can be developed. The objective of this study was to determine the effect of salt, a smoke compound, storage temperature, and their interactions on L. monocytogenes in simulated smoked salmon. A six-strain mixture of L. monocytogenes (10(2) to 10(3) CFU/g) was inoculated into minced, cooked salmon containing 0 to 10% NaCl and 0 to 0.4% liquid smoke (0 to 34 ppm of phenol), and the samples were stored at temperatures from 0 to 25 degrees C. Lag-phase duration (LPD; hour), growth rate (GR; log CFU per hour), and maximum population density (MPD; log CFU per gram) of L. monocytogenes in salmon, as affected by the concentrations of salt and phenol, storage temperature, and their interactions, were analyzed. Results showed that L. monocytogenes was able to grow in salmon containing the concentrations of salt and phenol commonly found in smoked salmon at the prevailing storage temperatures. The growth of L. monocytogenes was affected significantly (P < 0.05) by salt, phenol, storage temperature, and their interactions. As expected, higher concentrations of salt or lower storage temperatures extended the LPD and reduced the GR. Higher concentrations of phenol extended the LPD of L. monocytogenes, particularly at lower storage temperatures. However, its effect on reducing the GR of L. monocytogenes was observed only at higher salt concentrations (>6%) at refrigerated and mild abuse temperatures (< 10 degrees C). The MPD, which generally reached 7 to 8 log CFU/g in salmon that supported L. monocytogenes growth, was not affected by the salt, phenol, and storage temperature. Two models were developed to describe the LPD and GR of L. monocytogenes in salmon containing 0 to 8% salt, 0 to 34 ppm of phenol, and storage temperatures of 4 to 25 degrees C. The data and models obtained from this study would be useful for estimating the behavior of L. monocytogenes in smoked salmon.     

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.     

Combined antimicrobial effect of oregano essential oil and caprylic acid in minced beef

Oregano essential oil (OEO) and caprylic acid (CA) are highly aromatic natural antimicrobials with limited individual application in food. We proved their combined additive effect when used in meat. Application of 0.5% CA and 0.2% OEO (v/w) with 0.1% of citric acid in vacuum packed minced beef inoculated with Listeria monocytogenes at a concentration of 5 log cells/g reduced counts of lactic acid bacteria by 1.5 log CFU/g and counts of psychrotrophic bacteria and L. monocytogenes by more than 2.5 log CFU/g at the end of storage at 3 °C for 10 days. In sensory evaluation the samples with OEO showed during the whole experiment statistically better scores than control, whereas the samples treated with CA showed worse colour attributes.     

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.