Inactivation Of Listeria Innocua Research Articles

Scaling up gaseous chlorine dioxide (ClO2) treatment in the cold storage of fresh apples

Novel interventions are needed to mitigate microbial risks, like Listeria monocytogenes, before shipping fresh apples to retail markets. Batch gaseous chlorine dioxide (ClO2) in-storage treatments were conducted to assess the inactivation of Listeria innocua, reduction of spoilage microorganisms, and changes in quality. Gaseous ClO2 was generated using equal amounts of dry precursors inside the modified commercial refrigerator with 82 kg and 330 kg apples for pilot and semi-industrial scale experiments, respectively. A cocktail of L. innocua was spot inoculated on the calyx of fresh Fuji apples and treated with an initial ClO2 input of 1.2 g of each precursor/kg of produce at a pilot scale for 30 d and semi-industrial scale for 90 d. Headspace ClO2 concentrations, temperature, and relative humidity were measured during the batch treatments. Reductions of 1.4±0.2 and 1.2 log CFU/mL of Listeria innocua were achieved by pilot-scale and semi-industrial scale trials, respectively. The presence of spoilage microorganisms was not significantly (P>0.05) impacted, and apples displayed no signs of deterioration. This study confirms that ClO2 can significantly inhibit foodborne pathogens, such as Listeria, during prolonged cold storage and reduce the risk of contamination for apple growers.

Dynamic Thermal Treatments in Green Coconut Water Induce Dynamic Stress Adaptation of Listeria innocua That Increases Its Thermal Resistance.

The global coconut water market is projected to grow in the upcoming years, attributed to its numerous health benefits. However, due to its susceptibility to microbial contamination and the limitations of non-thermal decontamination methods, thermal treatments remain the primary approach to ensure the shelf-life stability and the microbiological safety of the product. In this study, the thermal inactivation of Listeria innocua, a Listeria monocytogenes surrogate, was evaluated in coconut water and in tryptone soy broth (TSB) under both isothermal (50-60 °C) and dynamic conditions (from 30 to 60 °C, with temperature increases of 0.5, 1 and 5 °C/min). Mathematical models were used to analyse the inactivation data. The Geeraerd model effectively described the thermal inactivation of L. innocua in both TSB and coconut water under isothermal conditions, with close agreement between experimental data and model fits. Parameter estimates and analysis revealed that acidified TSB is a suitable surrogate medium for studying the thermal inactivation of L. innocua in coconut water, despite minor differences observed in the shoulder length of inactivation curves, likely attributed to the media composition. The models fitted to the data obtained at isothermal conditions fail to predict L. innocua responses under dynamic conditions. This is attributed to the stress acclimation phenomenon that takes place under dynamic conditions, where bacterial cells adapt to initial sub-lethal treatment stages, leading to increased thermal resistance. Fitting the Bigelow model directly to dynamic data with fixed z-values reveals a three-fold increase in D-values with lower heating rates, supporting the role of stress acclimation. The findings of this study aid in designing pasteurization treatments targeting L. innocua in coconut water and enable the establishment of safe, mild heat treatments for refrigerated, high-quality coconut water.

Combining High-Pressure Processing and Supercritical Carbon Dioxide for Inactivation of Listeria innocua.

The effect of high-pressure treatment with supercritical CO2 on the inactivation of Listeria innocua in a fish soup was investigated. The soup was inoculated with L. innocua, packaged in modified atmosphere with 50:50 or 95:5 CO2:N2, high-pressure processed (300, 350, 400 and 600 MPa, 2 min) under subcritical (T < 304 K) or supercritical conditions (T > 304 K) and stored at 4 °C for up to 53 days. Treatment at 400 and 600 MPa had a significant (p < 0.05) effect on L. innocua under both supercritical and subcritical conditions. In contrast, pressurization at 350 MPa and supercritical conditions were needed to significantly (p < 0.05) inactive L. innocua. Increased levels of CO2 in the headspace significantly (p < 0.05) reduced the bacterial load during processing, and supercritical conditions had a significant (p < 0.01) interaction with both CO2 levels and pressure. Increased storage time gave significantly increased levels of L. innocua at 400 and 600 MPa. In addition, high levels of CO2 significantly decreased (p < 0.001) growth. However, 350 MPa under supercritical conditions seemed to set the L. innocua in a permanent lag phase, with slow and steadily decreasing numbers of bacteria during storage. All the design variables resulted in significant inactivation of L. innocua, and supercritical conditions combined with high levels of CO2 inhibited the recovery of L. innocua to a large degree.

Impact of voltage and pulse delivery mode on the efficacy of pulsed light for the inactivation of Listeria

Listeria innocua inactivation by pulsed light (PL) was evaluated at different settings and voltages, to establish the best treatment conditions and post-treatment handling for further implementation of PL in the food industry. Fluences up to 0.2 J/cm2 were applied to superficially inoculated TSA agar plates (4.5–5 log cfu/cm2). Inactivation was calculated, and log-linear and Weibull models were applied. A fluence of 0.2 J/cm2 applied in a single pulse inactivated 3.8 log cfu/cm2, while sequential application of this fluence yielded an inactivation between 1.5 and 2.5 log cfu/cm2 depending on the delivery mode (consecutive flashing or with 5 min-holding times under ambient light or in the dark). Data from consecutive PL treatment were fitted with the Weibull model. No photoreactivation following PL was observed after 120-min exposure to ambient light in any of the conditions assayed. This study showed that flashing with a single pulse at higher voltage would offer the highest inactivation of Listeria. Industrial relevanceThis study offered information of practical interest to establish pulsed light processing and post-processing conditions for the control of Listeria spp. in the food industry, for instance in ready-to-eat (RTE) products. The use of higher voltages provided higher inactivation and allowed to minimise the number of flashes. If sequential treatments are to be applied, the treatment is more effective if short holding times are kept between pulses. The post-processing illumination conditions do not influence the efficacy of PL treatment.

The effect of ultrasound treatment in combination with nisin on the inactivation of Listeria innocua and Escherichia coli

Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy.This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 – 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level.Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.

The impact of food model system structure on the inactivation of Listeria innocua by cold atmospheric plasma and nisin combined treatments

Novel processing methods such as cold atmospheric plasma (CAP) and natural antimicrobials like nisin, are of interest to replace traditional food decontamination approaches as, due to their mild nature, they can maintain desirable food characteristics, i.e., taste, texture, and nutritional content. However, the microbial growth characteristics (planktonic growth/surface colonies) and/or the food structure itself (liquid/solid surface) can impact the inactivation efficacy of these novel processing methods. More specifically, cells grown as colonies on a solid(like) surface experience a completely different growth environment to cells grown planktonically in liquid, and thus could display a different response to novel processing treatments through stress adaptation and/or cross protection mechanisms. The order in which combined treatments are applied could also impact their efficacy, especially if the mechanisms of action are complementary.This work presents a fundamental study on the efficacy of CAP and nisin, alone and combined, as affected by food system structure. More specifically, Listeria innocua was grown planktonically (liquid broth) or on a viscoelastic Xanthan gum gel system (1.5% w/v) and treated with CAP, nisin, or a combination of the two. Both the inactivation system, i.e., liquid versus solid(like) surface and the growth characteristics, i.e., planktonic versus colony growth, were shown to impact the treatment efficacy. The combination of nisin and CAP was more effective than individual treatments, but only when nisin was applied before the CAP treatment.This study provides insight into the environmental stress response/adaptation of L. innocua grown on structured systems in response to natural antimicrobials and novel processing technologies, and is a step towards the faster delivery of these food decontamination methods from the bench to the food industry.

Antilisterial effects of lysozyme-nisin combination at temperature and pH ranges optimal for lysozyme activity: Test of key findings to inactivate Listeria in raw milk

This study aimed to determine antilisterial potential of lysozyme (LYS)-nisin (NIS) combination at temperatures and pHs optimal for LYS activity. Tests in buffers at pH 4.5 and 6.0 showed that heating at 50 or 60 °C combined with LYS-NIS caused higher Listeria innocua inactivation (- 6.2 to >6.6 log) than heating alone (- 0.05 to 5.5 log), or heating combined with LYS (- 4.34 to 6.0 log) or NIS (3.9 to >6.6). The antimicrobial performance of LYS-NIS in buffer at 50 °C was not pH-dependant (5.8–5.9 logs) while heating at 60 °C with LYS-NIS at pH 6.0 (>6.6 logs) caused higher Listeria reduction than that at pH 4.5 (5.7 logs). Heating at 50 °C for 45 min alone or in combination with LYS-NIS caused 0 and 5.5 logs Listeria reduction in milk, respectively. In contrast, Listeria inactivation in milk at 60 °C occurred mainly by heat (5.5 logs) with limited contribution of LYS and/or NIS. Milk heated at 50 °C maintained 73% of NIS and 63% of LYS activity. Application of LYS-NIS at 50 °C provides an opportunity to improve milk safety with less destruction of milk enzyme and microbial flora necessary to obtain desired ripening periods, and aroma and flavour in traditional cheeses.

Inactivation of Listeria innocua on blueberries by novel ultrasound washing processes and their impact on quality during storage

We explored the efficacy of ultrasound in combination with carvacrol and carbonated water as a treatment to decontaminate fresh produce using blueberries as a model system. We also evaluated its impact on the quality of blueberries during refrigerated storage. Blueberries inoculated with Listeria innocua, a model pathogen, were washed in presence of individual treatments by either 20 kHz ultrasound at (20 kHz), 1 MHz ultrasound at (1 MHz), 2 mM carvacrol (CR), or carbonated water (CW) as well as their combinations at 20 °C for 10 min. Individual treatments resulted in around 2 log CFU/g L. innocua reductions on the blueberries' surface with 3–4 log CFU/mL viable bacteria remaining in the wash water. Comparatively, both 20 kHz + CR and 1 MHz + CR + CW led to significantly lower (P < 0.05) bacterial counts on blueberries’ surface (~1 log additional reduction) with 2.6 and 2.9 log CFU/mL in the washed water. 20 kHz + CR and 1 MHz + CR + CW treatments were selected to further investigate their effects on blueberry quality compared to washing with sodium hypochlorite (SH) containing 100 ppm free chlorine, or water during subsequent 4 °C storage for up to 20 days. Unwashed blueberries were used as control. Blueberries washed by selected treatments had equal or lower (P < 0.05) total aerobic and total mold and yeast counts compared to those treated by water, SH and the control. There was no influence of ultrasound washing processes on the total phenolic content and total anthocyanin content of blueberries, however, a significant impact on color and texture was observed. The findings showed that washing blueberries with novel combined ultrasound washing processes have the potential to enhance the safety and shelf-life of ready-to-eat blueberries.

Effect of production process and high-pressure processing on viability of Listeria innocua in traditional Italian dry-cured coppa.

In this study the effect of the application of High Pressure Treatment (HPP) combined with four different manufacturing processes on the inactivation of Listeria innocua, used as a surrogate for L. monocytogenes, in artificially contaminated coppa samples was evaluated in order to verify the most suitable strategy to meet the Listeria inactivation requirements needed for the exportation of dry-cured meat in the U.S. Fresh anatomical cuts intended for coppa production were supplied by four different delicatessen factories located in Northern Italy. Raw meat underwent experimental contamination with Listeria innocua using a mixture of 5 strains. Surface contamination of the fresh anatomical cuts was carried out by immersion into inoculum containing Listeria spp. The conditions of the HPP treatment were: pressure 593 MPa, time 290 seconds, water treatment temperature 14°C. Listeria innocua was enumerated on surface and deep samples post contamination, resting, ripening and HPP treatment. The results of this study show how the reduction of the microbial load on coppa during the production process did not vary among three companies (P>0.05) ranging from 3.73 to 4.30 log CFU/g, while it was significantly different (P<0.01) for the fourth company (0.92 log CFU/g). HPP treatment resulted in a significant (P<0.01) deep decrease of L. innocua count with values ranging between 1.63-3.54 log CFU/g with no significant differences between companies. Regarding superficial contamination, HPP treatment resulted significant (P<0.01) only in Coppa produced by two companies. The results highlight that there were processes less effective to inhibit the pathogen; in particular for company D an increase of L. innocua count was shown during processing and HPP alone cannot be able to in reaching the Listeria inactivation requirements needed for exportation of dry-cured meat in the U.S. According to the data reported in this paper, HPP treatment increases the ability of the manufacturing process of coppa in reducing Listeria count with the objective of a lethality treatment.

Impact of high-pressure and microwave-assisted thermal pasteurization on inactivation of Listeria innocua and quality attributes of green beans

In response to the increasing consumer demand for high-quality, minimally processed ready-to-eat (RTE) meals, the food industry has shown strong interests in exploring new processing technologies for production of safe RTE meals with an adequate shelf life in cold distribution chains. The purpose of this research was to understand the effect of high-pressure processing (HPP) and microwave-assisted thermal pasteurization on the quality attributes of green beans.The pasteurization conditions were selected as 600 MPa at 25 °C for 10 min for HPP and 70 °C for 2 min for processing with microwave-assisted pasteurization system (MAPS). Survival of L.innocua ATCC 51742 in green bean brine solution was analyzed right after the pasteurization processes. The quality attributes of the green beans, such as color, chlorophyll content, texture, vitamin C content, and pH, were further determined during storage at 2 °C for 36 days and 10 °C for 20 days.High-pressure treatment resulted in a 3.7-log CFU/g reduction in L. innocua ATCC 51742, whereas MAPS processing showed a 9.0-log CFU/g reduction. Both pasteurization processes provided significantly better green color retention when the beans were stored at 2 °C than when they were stored at 10 °C. Regardless of the pasteurization methods, the change in the greenness (a*) value of the beans followed similar trends during storage. Both methods caused an increase in the total color difference (ΔE) and a decrease in hue angle (yellowness) during storage (p < 0.05), but they had no significant effect on firmness, total chlorophyll content, and pH of the green beans. After the pasteurization processes, the vitamin C content of the HPP-treated green beans decreased significantly in comparison with the MAPS-treated beans (p < 0.05). This work reveals that both pasteurization treatments have a similar impact on quality attributes of green beans and that MAPS processing is more efficient in inactivating L. innocua ATCC 51742.

Non-thermal atmospheric gas plasma for decontamination of sliced cheese and changes in quality.

The atmospheric-pressure non-thermal dielectric barrier discharge (DBD) plasma has recently emerged as an efficient decontamination method for the food safety enhancement. Thus the objective of this study was to evaluate the effectiveness of a simple DBD plasma treatment, with a relatively low-frequency power supply operating at 60 Hz, for microbial inactivation. A parametric study of operating conditions for bacterial inactivation was conducted using nutrient agar inoculated with Escherichia coli (2.28--6.28 log CFU/ml). The microbial log reduction was enhanced with increasing input power (30, 50, 70 W) and plasma exposure time (0, 1, 3, 5, 7 min). The inactivation effect was increased by decreasing inter-electrode gap (2, 1.5, 1 cm) and by reducing the initial microorganism concentration. Accordingly, a DBD plasma treatment at 50 W for 10 min could lead to complete killing of E. coli and partial inactivation of Listeria innocua on cheese (mean log reduction: 4.75 ± 0.02 and 0.72 ± 0.01, respectively). The decontamination efficacy of DBD plasma was affected by the types of microorganisms. The changes in hardness and color of cheese were unnoticeable after 10 min treatment with a power of 50 W. Overall, the results suggested that the DBD plasma can be potentially exploited to improve the food safety.

In-situ monitoring of inactivation of Listeria innocua under high hydrostatic pressure using electrical conductivity measurement

The effect of high hydrostatic pressure on electrical conductivity of samples of Listeria innocua ATCC 33090 bacterial suspension (~1010 CFU/ml) was investigated, to determine if its inactivation could be monitored via such measurements. HHP treatment was applied at 300, 400 and 500 MPa, and the electrical conductivity, temperature and pressure were continuously recorded during experiments. Microbiological concentrations were also monitored by plate-counting over a 60 min hold period. With increasing pressure the degree of cell damage increased resulting in higher final electrical conductivity and higher reduction in Listeria innocua CFU. The log reduction in bacterial counts increased with increasing conductivity ratio. Conductivity ratio increased during pressurization and holding, but did not change during depressurization, suggesting that little or no inactivation occurred during this phase. Data on conductivity ratio, calibrated against microbial count reduction could be used to fit to inactivation kinetics models. A log-linear model with tail was found to provide the best fit.

The effect of Pulsed Light and starch films with antimicrobials on Listeria innocua and the quality of sliced cheddar cheese during refrigerated storage

The main goal of this study was to evaluate the effectiveness of a combination of antimicrobial films and Pulsed Light (PL) on inactivation of Listeria innocua on Cheddar cheese surface, and maintaining of product quality during refrigerated storage. The properties of antimicrobial starch films (ASF) containing sodium benzoate (ASF-SB), citric acid (ASF-CA), and both (ASF-CASB), prepared by casting and irradiated with PL, were evaluated. These films were used as packaging for Cheddar cheese slices that were surface inoculated with L. innocua at an initial inoculum level of 7 log CFU per cheese slice. PL had no effects on the structure of ASF. PL applied in combination with ASF-CA achieved an average of 4.5 log CFU reduction of L. innocua after 3 days of storage at 4 °C. However, significant changes in physicochemical properties of cheese, including pH, moisture level and mechanical properties, were observed after 7 days of refrigerated storage. These results suggest that, while PL-ASF can be effective in reducing L. innocua on Cheddar cheese surface, this combination treatment may induce some quality changes in the product.

Plasma-activated water as an alternative nitrite source for the curing of beef jerky: Influence on quality and inactivation of Listeria innocua

The aim of this study was to evaluate the potential of plasma-activated brine (PAB) as a nitrite source for the curing of beef jerky. The effects of PAB on quality parameters and on the microbial reduction of inoculated L. innocua were monitored. Beef slices were cured for ~18 h at 4 °C in brine solutions containing 0, 100 or 150 ppm of sodium nitrite, 150 ppm of sodium chloride (NaCl) and 100 ppm of sugar and subjected to plasma treatment. PAB were generated by a plasma beam system operating at 20 kHz and supplied with air or nitrogen (N2) gas. Results showed significant higher levels (p < .05) of nitrites in brines activated by air-plasma (90–184 ppm) compared to N2 gas (3–17 ppm). No significant differences were found in the texture and lipid oxidation levels of samples cured in PAB compared to standard curing. However, a significant higher a* value (6.45 ± 0.50, p < .001) was observed in samples cured in PAB. Significant reductions (p < .01) of 0.5 log CFU/mL in the population of L. innocua were observed in the brines and of 0.85 log CFU/g reduction in the jerky when cured in PAB. These results showed that plasma-curing could supply a suitable source of nitrite for meat products and, further optimisation of the technology could have applications for meat decontamination.

Inactivation of Listeria innocua on packaged meat products by pulsed light

Abstract Contaminations of food with Listeria monocytogenes pose a serious threat to human health, especially in case of chilled ready-to-eat products. Pulsed Light (PL) represents a promising technology to reduce microorganisms, including pathogens, on food surfaces. The application of intense light flashes of a broad spectrum (200–1100 nm) has been approved by the FDA in 1996 for food disinfection at a maximum fluence of 12 J/cm². Its mode of microbial inactivation is mainly attributable to DNA alterations as a result of UV-light exposure. In this study, the applicability of PL for disinfection of packaged frankfurter sausages (two different casings), sliced boiled ham and chicken cold cuts was investigated. Artificially inoculated product samples were packaged in PA/PE vacuum bags and subsequently PL treated (0.35 J/cm²–3.6 J/cm²) in order to assess the inactivation efficiency as well as the impact on the food quality. It was shown that PL treatments allow reductions of L. innocua by about 1 log on the surface of sliced boiled ham and chicken cold cuts while 3–4 log can be achieved on frankfurter sausages. The initial count reduction was maintained over 12 days of chilled storage (5 °C) and no impact on product color and appearance was observed. However, exposure to high PL doses induced significant sensory deviations which were identified by triangle tests. This study shows that moderate PL treatments, which provide distinct count reduction of pathogens while not affecting the product quality, can be a viable measure to increase food safety of packaged meat products.

Cold plasma treatment of ready-to-eat ham: Influence of process conditions and storage on inactivation of Listeria innocua.

Ready-to-eat (RTE) deli meat has been linked to several Listeria monocytogenes associated recalls. Recent studies demonstrated the potential antimicrobial effects of atmospheric cold plasma treatment on various food surfaces including RTE meat products. However, the influence of intrinsic and extrinsic factors, determining the efficacy of cold plasma to reduce Listeria has not been reported. This study investigated the influence of rosemary extract, salt (% NaCl), and treatment temperature on the efficacy of plasma to reduce numbers of L. innocua on RTE ham. The effect of post-treatment storage on L. innocua inactivation was also investigated. When the cold plasma treatment temperature was 4 °C, we observed a significant reduction in L. innocua of 1.75 and 1.51 log CFU/cm2 on 1% and 3% NaCl ham surface without rosemary extract respectively, after 180 s treatment. At a treatment temperature of 23 °C, the L. innocua cells were reduced by 1.78 and 1.43 log CFU/cm2, respectively on these surfaces after 180 s. No significant effects of salt concentration and treatment temperature were observed on L. innocua inactivation during cold plasma treatment of ham. The post treatment storage at 4 °C for 6 h after 180 s of plasma treatment enhanced further reduction of L. innocua on 1% NaCl ham without rosemary. We also observed the increased concentration of malondialdehyde (MDA) equivalent lipid oxidation of plasma treated samples and was significantly higher (1.53 MDA mg/ kg ham) compared to untreated samples (0.92 MDA mg/kg ham). However, no significant differences in surface color parameters, L* and b* values were observed after plasma treatment, except a significant increase in a* values. The water content of plasma exposed samples decreased significantly for all treatment conditions whereas the water activity values were not changed significantly. In conclusion, the atmospheric cold plasma could be applied as a means for surface decontamination of RTE ham. However, the drying and oxidation of ham should be controlled in an open atmospheric plasma treatment condition.

Inactivation of Listeria innocua and Escherichia coli in carrot juice by combining high pressure processing, nisin, and mild thermal treatments

This study explored the effectiveness of high pressure (200–500 MPa) alone or in combination with mild thermal treatments (35 and 50 °C) and nisin (25 and 50-ppm) on the inactivation of L. innocua and E. coli in carrot juice. Processing at 500 MPa at 20 °C for 2 min without nisin resulted in 4- and 5-log CFU/mL reduction of L. innocua and E. coli, respectively while incorporating 25-ppm nisin at same pressure and temperature rendered 7-log CFU/mL reduction. There was synergism between high pressure, nisin, and heat in all treatments to inactivate both microorganisms. After a 28-d of refrigerated storage, total plate counts were <2-log CFU/mL in carrot juice treated with combination of 300 MPa and 25-ppm nisin at 35 °C. All combinations resulted in less intense use of pressure, i.e. more energy efficient, cost effective processes while attaining high quality juices. The results of this study suggest that by using selected combinations of high pressure, nisin and mild temperatures, safe, clean-label, high-quality juices can be produced. The results from this study show a synergistic effect on the inactivation of L. innocua and E. coli in carrot juice from the combined application of HPP, nisin, and mild temperatures. By replacing the use of HPP alone by these combinations will allow the use of reduced pressures over shorter period of times to process low-acid juices, lowering energy requirements and increasing throughput. This study will aid the beverage processing industry in the development of clean label juice products with fresh-like quality attributes and using considerable less energy to conventional processing.

Effect of high voltage atmospheric cold plasma on inactivation of Listeria innocua on Queso Fresco cheese, cheese model and tryptic soy agar

High voltage atmospheric cold plasma (HVACP) is a novel technology which has shown promising results on microbial inactivation under low temperature, and thus offers opportunities on decontamination of biological materials. In this study, Listeria innocua spot inoculated tryptic soy agar (TSA), Queso Fresco cheese (QFC) and cheese model (CM) samples were treated with HVACP under direct and indirect mode of exposure in dry air gas environment for 5 min. After direct HVACP treatment, a reduction of 5.0, 3.5 and 1.6 log10 CFU/g was observed for TSA, CM and QFC, respectively. Direct plasma treatment was more effective in Listeria innocua inactivation on CM and QFC compared to indirect treatment. Surface analysis has shown that the differences in surface roughness and micro-structure of the substrate hugely impact the efficacy of the HVACP treatment by affecting the attachment of the bacteria cells on the surface and providing protective locations for the microbes within the surface.

High hydrostatic pressure inactivation and recovery study of Listeria innocua and Saccharomyces cerevisiae in pitaya (Stenocereus pruinosus) juice

Abstract The high hydrostatic pressure (HHP) inactivation of Listeria innocua and Saccharomyces cerevisiae was investigated in pitaya juice subsequently stored 15 d under refrigeration to assess recovery. Juice inoculated to 7.6 ± 0.4 or 7.3 ± 0.3 log10 (CFU mL−1) of L. innocua or S. cerevisiae, respectively, was treated at 400 to 600 MPa for 7.6 to 15 min (Tinitial = 19.5 ± 2.8 °C and Tmax = 34.6 ± 2.0 °C) following a Response Surface Design. Come-up time (CUT), defined as pressure release 1 s after reaching pressure set-point, was also evaluated. After a 400 MPa CUT treatment, no viable S. cerevisiae survivors were observed. Treatments at 550 and 600 MPa for 16 and 12 min, respectively, achieved L. innocua reductions exceeding 5-log10. No viable S. cerevisiae were observed when treated juice was stored at 4 ± 1 °C for up to 15 d. HHP appears a viable nonthermal alternative to produce a microbiologically safe and stable pitaya juice.

Effects of combined high pressure (HPP), pulsed electric field (PEF) and sonication treatments on inactivation of Listeria innocua

Suspensions of non-pathogenic Listeria innocua ATCC 33090 in water were exposed to different combinations of high hydrostatic pressure (HPP), pulsed electric field (PEF) and sonication treatments. Treatments were conducted individually, or in various combinations – sequential HPP-PEF; sequential PEF-HPP, simultaneous HPP-PEF, sequential HPP-sonication and sequential sonication-HPP. The greatest reduction by an individual treatment was obtained with HPP, wherein exposure to 400 MPa for 100 s resulted in an 8 log reduction in CFU. Both PEF (30 kV, 10−3 s) and sonication (250s) treatments gave about 2 log reduction in the Listeria population. Sequentially applied HPP-PEF, and PEF-HPP treatments demonstrated mostly additive effects. Notably, however, a synergistic effect was observed when PEF and HPP were applied simultaneously. Combinations of HPP and sonication treatments demonstrated synergistic effects when HPP treatment was followed by sonication, but additive effects when sonication was followed by HPP. A relationship between Listeria innocua inactivation and increase in the suspension zeta potential was observed. However, protein content of the supernatant was found insignificant, indicating that leakage from cells were non-protein cell constituents.