Inactivation kinetics of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni in ready-to-eat sliced ham using UV-C irradiation

To investigate the applicability of UV-C irradiation on the inactivation of foodborne pathogenic bacteria in ready-to-eat sliced ham, UV-C treatment was evaluated. Irradiation dose required for 90% reduction of the populations of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni were determined to be 2.48, 2.39, and 2.18 J/m². Ready-to-eat sliced hams were inoculated with the pathogens and irradiated with UV-C light of 1000, 2000, 4000, 6000, and 8000 J/m². Microbiological data indicated that foodborne pathogen populations significantly (p < 0.05) decreased with increasing UV-C irradiation. In particular, UV-C irradiation at 8000 J/m² reduced the populations of L. monocytogenes, S. Typhimurium, and C. jejuni in the ham by 2.74, 2.02, and 1.72 log CFU/g. The results indicate that UV-C irradiation can be used as a microbial inactivation method for ready-to-eat sliced ham, and inactivation kinetics of the foodborne pathogens fit the Weibull model better than the first-order kinetics model.     

Inactivation of foodborne pathogens in ready-to-eat salad using UV-C irradiation

To examine the applicability of ultraviolet (UV)-C irradiation on the inactivation of foodborne pathogen in ready-to-eat salad, it was inoculated with Escherichia coli O157:H7 and Listeria monocytogenes and then irradiated with UV-C light. Radiation dose required for 90% reduction (d _R) values of E. coli O157:H7 and L. monocytogenes were determined to be 0.21 and 2.48 J/m², respectively. Foodborne pathogen populations significantly (p<0.05) decreased with increasing UV-C irradiation. UV-C irradiation at 8,000 J/m² reduced the populations of E. coli O157:H7 and L. monocytogenes on ready-to-eat salad by 2.16 and 2.57 log CFU/g, respectively.     

Competitive interactions inside mixed-culture biofilms of Salmonella Typhimurium and cultivable indigenous microorganisms on lettuce enhance microbial resistance of their sessile cells to ultraviolet C (UV-C) irradiation

Salmonella Typhimurium (ST) is one of the leading causes of foodborne diseases in fresh produce, such as lettuce. Despite this, the role of the possible interactions between lettuce indigenous microorganisms and ST on their ability to form biofilm on lettuce and subsequently on the sensitivity of their sessile cells to ultraviolet C (UV-C) irradiation, remains relatively unexplored. Here, the interaction of a mixed-culture of ST and cultivable indigenous microorganisms (CIMs) was examined, as well as the efficacy of UV-C. Initially, the CIMs were isolated and cultured with ST at 15 °C either planktonically or left to form biofilms on stainless steel (SS) and lettuce leaves. Microbial growth, biofilm formation, and survival following UV-C treatment were monitored using traditional plate count methods while biofilm formation, production of extracellular polymeric substance (EPS), and stomatal colonization were also observed by field emission scanning electron microscopy (FESEM). Internalization strength, color, and texture were analyzed by standard methods. Results revealed that the mixed-culture of ST and CIMs presented significantly (p < 0.05) decreased biofilm formation on lettuce leaves compared to mono-cultures (i.e. ST or CIMs alone), which indicated competitive interaction between them, while no interactions were observed for biofilms on SS and for the planktonic cultures. It was also demonstrated that a mixed-culture biofilm on lettuce presented significantly higher resistance (p < 0.05) to UV-C treatment compared to mono-culture biofilms, but such an effect was not observed for biofilms formed on SS and for the planktonic cultures. The Weibull model fitted well to microbial inactivation curves with R² values that ranged from 0.90 to 0.97. Regarding the mixed-culture conditions, a UV-C fluency of 35 mJ/cm² was required to achieve a 5.0 log CFU/mL or cm² reduction in planktonic and biofilms on the SS for the mixed-culture, while 360 mJ/cm² was required to reduce biofilm cell number by approximately 2.0 log CFU/cm² on lettuce. Furthermore, FESEM analysis indicated higher EPS production, and greater stomatal colonization on lettuce mixed-cultures compared to mono-cultures. Finally, internalization strength was significantly higher (p < 0.05) for the mixed-culture on lettuce, thus supporting the notion that internalization in lettuce is a factor that contributes to microbial UV-C resistance. The absence of adverse effects of UV-C on the color and texture of the lettuce suggests it as an alternative means of eliminating ST.     

UV-C irradiation as an alternative disinfection technique: Study of its effect on polyphenols and antioxidant activity of apple juice

Ultraviolet (UV-C) irradiation is a non-thermal disinfection method, effective against a range of bacteria and viruses, which is being considered as an alternative to pasteurization of fruit juices. The objective of this study was to investigate the effect of UV-C irradiation on the polyphenolic content and in-vitro total antioxidant activity of apple juice. UV irradiation doses ranging from 0 to 240 mJ·cm^− 2 were delivered to apple juice and polyphenols, sugars, in-vitro total antioxidant activity and total phenols were profiled. The results demonstrated that UV-C irradiation in apple juices at relevant commercial disinfection doses induced significant reduction in the concentrations of chlorogenic acid, phloridzin, and epicatechin (p < 0.05). The induced changes were relatively minor for the above mentioned polyphenols, except phloridzin (50% reduction) at 240 mJ·cm^− 2. Epicatechin concentrations were reduced significantly (p < 0.05), whereas increase in catechin concentration was observed with increase in UV-C exposure to 240 mJ·cm^− 2. There was a minor reduction in sugar (glucose and fructose) concentrations with increasing exposure levels from 0 to 40 mJ·cm^− 2 (p > 0.05). In contrast, a slight increase in sugar concentrations as increase in UV-C exposure after 40 mJ·cm^− 2 was observed. These changes were not significantly different from control. Total phenolic content was well retained regardless of the UV-C exposure for apple juice. In-vitro total antioxidant activity changed when UV-C exposure exceeded 40 mJ·cm^− 2, but remained unchanged at the maximum UV-C dose of 240 mJ·cm^− 2. These results suggested that UV-C irradiation could be an effective alternative to conventional thermal processing for production of high quality apple juice.Industrial RelevanceThis research paper provides scientific evidence of the potential for UV-C irradiation to achieve meaningful levels of disinfection while retaining important bioactive compounds (polyphenols) in apple juice. In-vitro antioxidant activity and individual polyphenols were well retained at commercially relevant doses of 40 mJ·cm^− 2. From a nutritional perspective, UV-C irradiation is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore, UV-C irradiated foods could be sold at a premium price to their thermally-processed counterparts, as they have retained their fresh-like properties. This study would provide technical information relevant for commercialization of UV-C treatment of juices.     

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.     

Inactivation of Salmonella typhimurium and Lactobacillus plantarum by UV-C light in flour powder

This research evaluates the potential use of ultraviolet C light (UV-C) as a decontamination method for powdered foods, particularly of refined flour. This technology's lethal effectiveness was evaluated on Salmonella enterica subsp. Enterica serotype Typhimurium and Lactobacillus plantarum in wheat flour, and in laboratory liquid media of different a_w and turbidities to evaluate the action mechanisms of UV-C light in powdered products. Initial results showed a large variability of lethality in flour, obtaining between 0.2 and 3.0 log₁₀ cycles of inactivation. Results obtained in laboratory media and SEM analysis of contaminated flour indicated that the variability was due to a shadow effect on the efficacy of UV-C light and not due to the low water a_w of the flour or starch content. Based on these conclusions, a 2-m vertical tunnel with twelve 480 W UV-C lamps was designed to treat flour by forming a continuous cloud of dust (0.05–2.4 kg/h). Inactivation levels of 4.0 to 1.7 log₁₀ cycles of the population of L. plantarum in flour were achieved at flow rates of 0.2 and 2.4 kg/h respectively, with a maximum residence time of 4 s.Industrial relevanceThis investigation demonstrated the lethal efficacy of the application of UV–C light to inactivate microorganisms, both pathogenic and spoilage, present in flour. 4-log10 cycles of inactivation of both Salmonella Typhimurium and Lactobacillus plantarum were inactivated with UV-C treatments. A UV-C facility was built up which enabled to treat flour in continuous conditions creating a cloud of dust with treatments of 4 s and lethalities of 4-log10 reductions.     

Radio-sensitivity of pathogens in inoculated prepared foods of animal origin

The effectiveness of irradiation for inactivating Staphylococcus aureus, Listeria ivanovii, Salmonella Typhimurium, and Escherichia coli in the prepared foods of animal origin was investigated. Commercially available seasoned and cooked beef, fried egg, and ham were purchased, radiation-sterilized, and inoculated at 10⁶–10⁷ CFU/g with each of the four pathogens and stored at three storage conditions at 10 °C, 20 °C, and 30 °C. D₁₀-values of S. aureus, L. ivanovii, Salmonella Typhimurium, and E. coli were 0.34±0.01, 0.24±0.02, 0.24±0.01, and 0.27±0.01 kGy, respectively. No viable cells were detected at 3 kGy of irradiation. Salmonella mutagenicity assay (Ames test) indicated that the 10 kGy irradiated samples were statistically similar to non-irradiated control samples in the Salmonella mutagenicity assay (Ames test). These studies demonstrate that irradiation can be used as an additional safety tool to produce microbiologically safe and wholesome prepared foods of animal origin.     

High pressure carbon dioxide combined with high power ultrasound processing of dry cured ham spiked with Listeria monocytogenes

Traditionally, thermal treatments for the inactivation of Listeria monocytogenes in meat products involve undesirable changes of the product quality. In recent years, efforts have been carried out to develop alternative methods to inactivate L. monocytogenes without affecting the product quality attributes. In this context, the feasibility of combined high pressure carbon dioxide and high power ultrasound (HPCO₂ + HPU) treatment to inactivate L. monocytogenes inoculated on the surface of dry cured ham was investigated. Inactivation data were determined at 6, 8 and 12 MPa, as a function of temperature (22, 35, 45 °C) and treatment time (0.5 to 30 min), and compared to those obtained after thermal and HPCO₂ treatments.Color, pH and acidity changes of the samples after both thermal and HPCO₂ + HPU treatments were measured and compared, sensorial profile of the treated samples was evaluated by a sensory panel and shelf-life was determined by a storage study for 4 weeks at 4 °C.The results clearly revealed that HPU alone was not able to induce any microbial inactivation while HPCO₂ + HPU treatment always assured a certain level of inactivation, variable with the process temperature used: the inactivation efficiency was demonstrated higher at 35 °C rather than 22 °C and no enhancement was observed at 45 °C compared to 35 °C. Process conditions of 12 MPa, 35 °C, at 10 W for 5 min assured inactivation to undetectable level of L. monocytogenes spiked on the surface of the product with an initial concentration of about 10⁹ CFU/g. No differences were detected between acidity, pH, color and sensory attributes of the untreated and HPCO₂ + HPU treated dry cured ham surface, while slight differences were measured between the values obtained for the untreated and thermally treated samples. Additionally, the storage study demonstrated that a full microbial and quality shelf-life was assured for 4 weeks at 4 °C. The results obtained may open the doors to the application of such an innovative process at industrial level, in particular to treat ham-type or meat products.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in milk by caprylic acid and monocaprylin

Listeria monocytogenes and Escherichia coli O157:H7 are major foodborne pathogens implicated in various outbreaks involving pasteurized or unpasteurized milk, and various dairy products. The objective of this study was to determine the antibacterial effect of caprylic acid (CA, C_8:0) and its monoglyceride, monocaprylin (MC) on L. monocytogenes and E. coli O157:H7 in whole milk. A five-strain mixture of E. coli O157:H7 or L. monocytogenes was inoculated in autoclaved milk (10⁶ CFU/ml) containing 0, 25, or 50 mM of CA or MC. At 37°C, all the treatments, excepting 25 mm CA, reduced the population of both pathogens by approximately 5.0 log CFU/ml in 6 h. At 24 h of storage at 8°C, MC at both levels and CA at 50 mM decreased L. monocytogenes and E. coli O157:H7, respectively by >5.0 log CFU/ml. At 48 h of 4°C storage, populations of L. monocytogenes and E. coli O157:H7 were decreased to below detection level (enrichment negative) by 50 mm of MC and CA, respectively. Results indicate that MC could potentially be used to inhibit L. monocytogenes and E. coli O157:H7 in milk and dairy products, but sensory studies need to be conducted before recommending their use.     

Combinations of nisin with organic acids or salts to control Listeria monocytogenes on sliced pork bologna stored at 4°C in vacuum packages

This study evaluated dipping solutions of nisin with or without organic acids or salts, as inhibitors of Listeria monocytogenes introduced on sliced cooked pork bologna before vacuum packaging and storage at 4°C for 120 days. Inoculated (10²–10³ cfu/cm²) slices were immersed in nisin (5000 IU/ml), or in lactic or acetic acid (1, 3, 5 g/100 ml), sodium acetate or diacetate (3, 5 g/100 ml), and potassium benzoate or sorbate (3 g/100 ml), each combined with nisin. Additional slices were immersed in nisin, inoculated and then immersed in acid or salt solutions without nisin. Nisin reduced L. monocytogenes by 1.0–1.5 log cfu/cm² at treatment (day-0) followed by a listeriostatic effect for 10 days. Thereafter, however, the pathogen multiplied in treatments without acid or salts, with growth being faster on slices immersed in nisin after as compared to before inoculation. Nisin in combination with 3 or 5 g/100 ml acetic acid or sodium diacetate or 3 g/100 ml potassium benzoate, applied individually or as mixtures, did not permit growth before day-90. Other treatments were of variable and lesser effectiveness (20–70 days), whereas in untreated or water-treated (control) bologna L. monocytogenes increased at 6–7 log cfu/cm² at day-20. Based on the antilisterial efficacy and effects of treatments on product pH, nisin with 3 g/100 ml sodium diacetate may be the most promising combination in dipping solutions to control L. monocytogenes on sliced cured pork bologna.     

Efficacy of plant extracts in inhibitingAeromonas hydrophilaandListeria monocytogenesin refrigerated,cooked poultry

Alcohol extracts of angelica root, banana purée, bay, caraway seed, carrot root, clove (eugenol), marjoram, pimento leaf and thyme were applied to cooked chicken to determine their antimicrobial activities against Aeromonas hydrophilaand Listeria monocytogenes.Skinless chicken breast meat was cooked to an internal temperature of 85°C, allowed to cool to c. 5°C, then treated by surface application with plant extracts. Low (10 cfu g⁻¹)or high (10⁵ cfu g⁻¹)populations of A. hydrophilaand L. monocytogeneswere applied and samples were stored at either 5 or 15°C for up to 14 or 7 days, respectively. Eugenol and pimento extracts were most effective in inhibiting growth of both bacteria. A. hydrophilawas the more sensitive to the two treatments, with 4 log₁₀ cfu g⁻¹less growth occurring at 14 days at 5°C on eugenol-treated breast meat than on control samples. These results suggested that plant extracts might be useful as antimicrobials in cooked, ready-to-eat chicken meat.     

Reuterin,lactoperoxidase, lactoferrin and high hydrostatic pressure treatments on the characteristics of cooked ham

The effect of reuterin, lactoperoxidase system (LPS) and lactoferrin (LF) combined with high hydrostatic pressure (HHP) on the characteristics of sliced cooked ham during 35 days at 4 and 10 °C were investigated. Reuterin and LPS inhibited the growth of total microorganisms during 35 days at 4 and 10 °C, whereas a regrowth at 10 °C was observed when HHP was applied. Combined treatments kept total viable counts below 1.5 log cfu/g after 35 days at 10 °C. Regarding the effect of treatments on colour of cooked ham, LPS alone or in combination with HHP slightly affected L*, a* and b* values, but these changes tended to attenuate during storage. Likely, slight differences were registered in shear strength values among control and treated cooked ham. The accumulation of volatile compounds was reduced in cooked ham treated with LPS and LF in combination with HHP, even under abuse temperature conditions (10 °C).Industrial relevanceLPS applied in combination with HHP was the most effective treatment at reducing the growth of total microorganisms in refrigerated cooked ham with minor changes in its characteristics. The antimicrobial activity of such combined treatment against food-borne pathogens, which has also been reported in RTE foods, points to its usefulness to assure a safe product of sensory characteristics similar to those of untreated cooked ham.     

Processing of clear and turbid grape juice by a continuous flow UV system

The inactivation of inoculated (S. cerevisiae) and spoilage microorganisms, i.e. yeasts and lactic acid bacteria (LAB), in clear and turbid grape juice was investigated using a pilot scale UV system. The biodosimetry method was used for UV dose prediction in a continuous flow UV reactor. Weibull model was applied for fitting the inactivation data. The flow rates (774, 820 ml/min) in this system were very close to the ones used in fruit juice processing. S. cerevisiae in clear juice was reduced by 3.39 ± 0.04 at 65.50 mJ/cm² of UV dose. 1.54 ± 0.04 and 1.64 ± 0.03 log CFU/ml reductions were obtained for spoilage yeasts and LAB in turbid juice at UV dose of 78.56 and 67.97 mJ/cm², respectively. The soluble solids (°Brix) and pH of grape juice samples were not affected by UV-C treatment (p > 0.05). Although the color parameters slightly were changed after irradiation, the color of PCGJ and FSTGJ did not show visual difference compared to the untreated samples.Industrial relevanceUV light has a potential to reduce the levels of microbial contamination in liquid foods. Although grape juice has many beneficial health effects, it has a fairly short shelf life. Therefore, pasteurization is required. But the thermal pasteurization has some undesired effects on the juice quality. Consumer demands for high quality fruit juice with fresh-like characteristics have markedly expanded in recent years. In the current study, the microbial inactivation efficiency of a pilot scale UV system for non-thermal treatment of clear and turbid grape juice was evaluated under conservative conditions. Most of the physicochemical properties of grape juice samples were not significantly affected from UV-C treatment (p > 0.05). This would be a major advantage in the processing of nutritious juice products.     

Inactivation of food spoilage bacteria by high pressure processing: Evaluation with conventional media and PCR–DGGE analysis

Microbial diversity and dynamic changes of sliced vacuum-packed cooked ham during refrigerated storage (0–90 days) after high pressure processing (400 MPa at 22 °C for 10 min) was investigated by using culture-dependent and culture-independent approaches. Isolation of genome DNA and total RNA directly from meat samples, followed by PCR–denaturing gradient gel electrophoresis (DGGE) and RT-PCR–DGGE on 16S rDNA V3 region, was performed to describe the structure of the bacterial community and active species in pressurized sliced cooked ham. The DGGE profile showed that most spoilage bacteria including Lactococcus garvieae, Weissella cibaria, Lactobacillus sakei, Lactobacillus curvatus, Weissella paramesenteroides, Leuconostoc carnosum and Lactococcus lactis subsp. lactis were completely inactivated after high pressure processing (HPP), whereas Weissella viridescens and Weissella minor survived HPP and induced the final spoilage. The microbial diversity of HPP samples during the whole refrigerated storage period was extremely simple. Our results clearly indicated that HPP was an efficient method for avoiding the growth of the major spoilage bacteria and could be used to prolong the shelf-life of sliced vacuum-packed cooked ham.     

Survival of Listeria monocytogenes in Galotyri,a traditional Greek soft acid-curd cheese,stored aerobically at 4°C and 12°C

Galotyri is a traditional Greek soft acid-curd cheese, which is made from ewes’ or goats’ milk and is consumed fresh. Because cheese processing may allow Listeria monocytogenes post-process contamination, this study evaluated survival of the pathogen in fresh cheese during storage. Portions (0.5 kg) of two commercial types (<2% salt) of Galotyri, one artisan (pH 4.0±0.1) and the other industrial (pH 3.8±0.1), were inoculated with ca. 3 or 7 log cfu g⁻¹ of a five-strain cocktail of L. monocytogenes and stored aerobically at 4°C and 12°C. After 3 days, average declines of pathogen's populations (PALCAM agar) were 1.3–1.6 and 3.7–4.6 log cfu g⁻¹ in cheese samples for the low and high inocula, respectively. These declines were independent (P>0.05) of the cheese type or the storage temperature. From day 3, however, declines shifted to small or minimal to result in 1.4–1.8 log cfu g⁻¹ of survivors at 28 days of storage of all cheeses at 4°C, indicating a strong “tailing” independent of initial level of contamination. Low (1.2–1.7 log cfu g⁻¹) survival of L. monocytogenes also occurred in cheeses at 12°C for 14 days, which were prone to surface yeast spoilage. When ca. 3 log cfu g⁻¹ of L. monocytogenes were inoculated in laboratory scale prepared Galotyri of pH ≅4.4 and ≅3% salt, the pathogen died off at 14 and 21 days at 12°C and 4°C, respectively, in artisan type cheeses fermented with the natural starter. In contrast, the pathogen survived for 28 days in cheeses fermented with the industrial starter. These results indicate that L. monocytogenes cannot grow but may survive during retail storage of Galotyri despite its low pH of or slightly below 4.0. Although contamination of Galotyri with L. monocytogenes may be expected low (<100 cfu g⁻¹) in practice, that long-term survival of the pathogen in commercial cheeses was shown to be unaffected by the artificial contamination level (3 or 7 logs) and the storage temperature (4°C or 12°C), which should be a concern.     

Minimal processing of mucilage from the pulp of yam (Dioscorea pseudojaponica Yamamoto) using bubble separation and ultraviolet irradiation

Recently the applications of the low starch contents of yam mucilage in nutraceutical and cosmeceutical industries are required. A novel continuous pilot-scale bubble separation system was used for recovering yam slurry mucilage. The objectives of these studies were to follow the previous design for continuously separating, recovering and irradiating yam slurry mucilage for inactivation of microorganisms. The UV-C dose of 32000 μW/sec/cm² at 254 nm has a germicidal effect against microorganisms and is used for the disinfection. Two sets of custom made UV-C irradiators containing four UV-C germicidal lamps were added to the system. The effectiveness of this UV-C irradiator for reducing the aerobic bacteria count (APC) and yeasts and molds (YM) count in yam slurry mucilage was investigated. The results showed UV-C irradiation was successfully applied to reduce the microbial load in the yam slurry mucilage. If the slurry mucilage completes the process for both two sets of UV-C irradiators, a 4.5 log₁₀ APC reduction and a 4.1 log₁₀ YM reduction were achieved after 200 sec irradiation at a UV-C dosage of 32000 μW/sec/cm², resulting in zero cfu/ml APC and YM. Escherichia coli and Salmonella are both negative. This novel continuous UV-C pilot-scale bubble separation technology could be an alternative technology not only separate and recover mucilage but also reduce the microorganisms to acceptable levels.Industrial relevanceThis novel continuous pilot-scale bubble separation system was used for recovering yam slurry mucilage. Recently the applications of the low starch contents of yam mucilage in nutraceutical and cosmeceutical industries are required.This novel continuous UV-C pilot-scale bubble separation technology could be an alternative technology not only to separate and recover mucilage but also reduce the microorganisms to acceptable levels. Actually the pilot scale of this system is going to build in our university. We also try to further use it for non-thermal fermentation. There are many potential industrial applications using this idea.     

Considerations for post-lethality treatments to reduce Listeria monocytogenes from fully cooked bologna using ambient and pressurized steam

During processing of ready-to-eat (RTE) deli meats, any secondary processing procedures such as peeling and cutting introduce the distinct possibility of cross-contamination between equipment, personnel, and food. To eliminate or reduce pathogens such as Listeria monocytogenes and ensure food safety, RTE deli meats can be pasteurized prior to or after packaging. In this study, ambient steam in-package pasteurization was compared with pressurized steam prepackaging pasteurization to reduce L. monocytogenes from fully cooked RTE bologna. The bologna (14 cm diameter×1.5 cm thickness) samples were surface-inoculated to contain about 8 log₁₀ of L. monocytogenes. To achieve 2 log reductions for L. monocytogenes, the bologna samples needed to be treated for about 10 s in pressurized steam at 131 °C or for about 2.5 min in ambient steam at 100 °C. The pasteurization time using pressurized steam treatment was about 75–90% shorter than using ambient steam treatment. Pressurized steam treatment may be integrated into a vacuum packaging unit to effectively eradicate L. monocytogenes from RTE meats just prior to sealing the retail packages to further reduce the treatment time, avoid post-treatment recontaminations by pathogens, and improve food safety without detrimentally affecting meat quality.     

Pathogen inactivation and quality changes in sliced cheddar cheese treated using flexible thin-layer dielectric barrier discharge plasma

Cheese is recognized as a source of food-borne disease outbreaks worldwide. In this study the inactivation of pathogens on sliced cheddar cheese by using flexible thin-layer dielectric barrier discharge (DBD) plasma and its effect on food quality have been described. Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium populations on agar plates were significantly reduced by plasma treatment. The level of these microorganisms on sliced cheddar cheese in response to 10-min plasma treatment significantly decreased by 3.2, 2.1, and 5.8 Log CFU/g, respectively. The pH and L*-values decreased whereas thiobarbituric acid reactive substances values and b*-values increased significantly with extended exposure of the sliced cheddar cheese to DBD plasma. The total color difference (∆E), sensory appearance and color scores showed no significant differences between DBD plasma-treated and untreated sliced cheddar cheese. However, significant reductions in flavor and overall acceptance as well as an increase in off-odor were observed. These results indicate that flexible thin-layer DBD plasma can be used to sanitize food products, but conditions should be optimized for industrial applications.     

Modeling the protective effect of aw and fat content on the high pressure resistance of Listeria monocytogenes in dry-cured ham

High pressure processing (HPP) is a promising food preservation technology as an alternative to thermal processing for microbial inactivation. The technological parameters, the type of microorganism, and the food composition can greatly affect the microbicidal potential of HPP against spoilage and pathogenic microorganisms. Presently, the number of available models quantifying the influence of food characteristics on the pathogen inactivation is scarce. The aim of this study was to model the inactivation of Listeria monocytogenes CTC1034 in dry-cured ham, as a function of pressure (347–852 MPa, 5 min/15 °C), water activity (a_w, 0.86–0.96) and fat content (10–50%) according to a Central Composite Design. The response surface methodology, based on the equation obtained with a stepwise multivariate linear regression, was used to describe the relationship between bacterial inactivation and the studied variables. According to the best fitting polynomial equation, besides pressure intensity, both a_w and fat content exerted a significant influence on HP-inactivation of L. monocytogenes. A clear linear piezoprotection trend was found lowering the a_w of the substrate within the whole range of tested pressure. Fat content was included in the model through the quadratic term and as interaction term with pressure, resulting in a particular behavior. A protective effect due to the presence of high fat content was identified for pressure treatments above ca. 700 MPa. At lower pressure, higher inactivation of L. monocytogenes occurred by increasing the fat content above 30%. The results emphasize the relevant influence of intrinsic factors on the L. monocytogenes inactivation by HPP, making necessary to assess and validate the effectiveness of HPP on specific food products and consequently set process criteria adjusted to each particular food product.