Post-packaging Pasteurization Research Articles

The effect of post-packaging pasteurization on physicochemical and microbial properties of beef ham

In this study, we aimed to investigate the impact of three different post-packaging pasteurization temperatures (55, 65, and 75°C) on the physicochemical (pH, drip loss, texture profile, and color), microbial (lactic acid bacteria, mesophilic and psychrotrophic bacteria, as well as mold and yeast), and sensory (odor, taste, texture, color, slime, exudates, swelling, and overall acceptability) characteristics of vacuum-packed beef ham during 30 days of storage at two different temperatures (5 and 12°C).
 Lactic acid bacteria and total mesophilic and psychrotrophic counts were reduced to zero by post-packaging pasteurization at 65 and 75°C. Higher post-packaging pasteurization temperatures resulted in a significant increase in drip loss in the treated samples at 65 and 75°C, as well as a small rise in pH in all the samples. Furthermore, higher post-packaging pasteurization temperatures decreased lightness, yellowness, and h° values while increasing redness and ΔE. During post-packaging pasteurization, Chroma remained constant. The textural profile analysis revealed that post-packaging pasteurization and storage had a significant impact on the texture of beef ham. The sensory analysis showed no changes after post-packaging pasteurization in the samples, and the sensory parameters remained stable during their storage at 65 and 75 °C.
 Finally, our investigation showed that 65°C is an optimal post-packaging pasteurization temperature for increasing the shelf-life of beef ham under refrigeration.

Effects of post‐packaging pasteurization process on microbial, chemical, and sensory qualities of ready‐to‐eat cured vacuum‐packed Turkey breast

AbstractReady‐to‐eat (RTE) cured vacuum‐packed turkey breast was pasteurized (80°C, 5.5 min) and stored at 8°C (like supermarkets refrigerator temperature). After 42 days (current shelf life of this product), in control group (RTE cured vacuum‐packed turkey breast), the number of mesophilic, anaerobic, lactic acid bacteria, mold and yeast, coliform, and psychrotrophic increased 5.82, 6.85, 5.85, 4.75, 1.49, and 5.57 log CFU/g, respectively. However, in the pasteurized samples, the number of mesophilic, anaerobic, and lactic acid bacteria increased 1.86, 2.12, and 2.28 log CFU/g, respectively, and mold and yeast, coliform, and psychrotrophic bacteria were under the detection limit. The effects of post‐packaging pasteurization on the reduction of total mesophilic, anaerobic and lactic acid bacteria counts on Day 42 of storage was 7.04 ± 0.33, 4.73 ± 0.11, and 5.58 ± 0.11 log CFU/g, respectively. Sensory quality of treated samples was significantly better than the control's (p < .05). Post‐packaging pasteurization (PPP) significantly inhibited the reduction in the pH and the increase in TVB‐N, TBARS, titratable acidity, and drip loss (p < .05). This study shows the effectiveness of PPP on microbial, chemical, and sensory quality of cured vacuum‐packed turkey breast during cold storage.

Stability of postpackage pasteurized camu-camu pulp

Camu-camu ( Myrciaria dubia ) is a wild fruit native to the Amazon, with great nutritional potential due to high ascorbic acid content. As transport reduces its shelf life and fresh consumption is limited because of high acidity, posing obstacles to commercialization, pulping and pasteurization can enhance its shelf life. This study aimed to verify camu-camu pulp stability after postpackage pasteurization, using high barrier polypropylene bags, assessing physical and chemical alterations caused by cold (5 oC), frozen (-18 oC), and room temperature (28 oC) storage for 45 days. Samples were pasteurized in tanks at 75 °C for 1 min and rapidly cooled to room temperature. Frozen pulp presented the best physical and chemical characteristics, but cold stored samples also showed promising results, maintaining the initial characteristics throughout the study. Room-temperature storage may be a cheaper option to preserve the product, provided that natural dyes and flavor enhancers are added, since pH and acidity did not change during storage.

Effects of Plant Extract Addition on Listeria Monocytogenes Growth in Highly Extended Sliced Cooked in Ham

ObjectivesThe objective of this study was to evaluate the effect of a plant extract blend containing rosemary and citrus extract on controlling the growth of Listeria monocytogenes in highly extended sliced cook-in ham during refrigerated storage at 7°C.Materials and MethodsThe experiment comprised 2 treatments, control (no plant extract addition) and 0.4% of rosemary-citrus extract blend (Cleanatis M1, Naturex). This study was conducted using a standard ham formulation yielding an end product weighing 170% of the raw material used, in this case pork leg meat cuts. The different ham muscles obtained from the pork leg were injected with a brine solution containing water, sodium chloride, phosphates, sodium nitrite, sodium erythorbate, hydrolyzed corn syroup 40DE, monosodium glutamate, carrageenan and aromas. Each lot included one batch of samples tumbled (7 cycles/min) under vacuum, at controlled temperature between 0 and 4°C for 9 h and stuffed in polyamide impermeable casings (60 mm diameter to form cooked ham pieces with approximately 1.2 kg each. The ham pieces were cooked in water tanks (80°C) at a commercial pilot plant to reach 72°C. Cooking time was approximately 1 h and 30 min. After the cooking stage, samples were cooled with ice and refrigerated at 0 to 4°C overnight The ham pieces were transported to CTC/ITAL on ice box and immediately sliced for microbiological analysis at arrival. The ham slices (2 to 3 mm) were inoculated with 0.1 mL of of L. monocytogenes ATCC7644, to yield approximately 4 log CFU/g. Inoculated samples were vacuum packaged in gas-impermeable pouches and stored at abuse temperature (7°C), very common in Brazilian retail market, for up to 16 d. Bacterial populations were determined following ISO 11290–2:2017 method. Triplicate samples of each treatment were assayed at 0 time and after 2, 4, 6, 8, 10, and 12 d of storage for L. monocytogenes populations. In addition, triplicate inoculated samples were assayed for lactic acid bacteria populations following ISO 15214:1998 method. Data Interactions and main effects were considered significant at P < 0.05. The data were submitted to analysis of variance to evaluate the effect of the treatments, storage time and the treatment × time interaction using Statistica 7.0 (StaSoft Inc). The difference between the mean values was evaluated by Tukey´s test at the 95% confidence level.ResultsDuring storage, the difference between L. monocytogenes counts in the treatment containing the plant extracts and control was 0.5 log CFU/g. There was a significant effect (P < 0.05) of the interaction treatment versus time on L. monocytogenes growth, the counts remained 0.5 log lower on samples containing the plant extract blend. Lactic acid bacteria counts were below 1.0 Log CFU/g during shelf life for both treatments.ConclusionThese data suggest that the plant extracts blend can enhance the safety of sliced cook in ham. It is important to evaluate the effect in meat systems without nitrite addition or along with other interventions that inhibit growth, like post packaging pasteurization.

Application of high pressure processing for prevention of greenish-gray yolks and improvement of safety and shelf-life of hard-cooked peeled eggs

Abstract Hard-cooked peeled eggs (HCEs) are value-added ready-to-use egg products susceptible to microbial re-contamination during post-processing stages. A post-processing terminal step using high hydrostatic pressure (HHP 500, 550, 600 MPa for 5 min at 25 °C) was applied to ensure maximum safety of HCEs and the effects of processing were evaluated and compared with a commercial thermal post-processing intervention using steam heating. A significant discoloration in the form of greenish-gray yolks was observed in HCEs after steam heat post-processing due to overcooking. Color values of the HCE yolk (L*, a*, b*) after HHP post-processing were not significantly different (P > 0.05) from non-post-processed HCEs. Non-thermal and thermal post-processing interventions each kept the growth of microbial contaminants at 4 CFU/g throughout 45 days of refrigerated storage. Microbial counts in non-post-processed HCEs exceeded this safety limit within 3 d. Sensory analysis showed significantly higher preference scores for the quality attributes of HCEs post-processed with HHP than with steam heating. Inactivation curves of Salmonella Enteritidis inoculated onto HCE surfaces after all HHP levels were well-fitted to the biphasic mathematical model. HHP post-package pasteurization at 550 MPa for 5 min showed potential as a terminal non-thermal kill step for commercial production of HCEs. Industrial relevance A non-thermal post-processing intervention using HHP can be considered as a terminal kill step during commercial production of HCEs to ensure maximum microbiological safety and to extend the shelf life of HCEs without formation of unappetizing greenish-gray yolks. The biphasic mathematical model can be used to predict growth and survival of Salmonella Enteritidis in HCEs and to conduct a risk analysis of this type of food products.

Ultrasound-assisted post-packaging pasteurization of sausages

Ultrasound (US) is proposed to reduce temperature and accelerate the process of pasteurization of packaged hot dog sausages. They were pasteurized in an ultrasonic bath (25 kHz, 200 W) for 10.53 min at 74 °C with (US) and without ultrasound (WUS) and also with conventional pasteurization (CT, water bath at 82 °C, 16 min to reach 73 °C inside of sausages). The temperature was 3.9 °C higher inside of pasteurized sausages using US in comparison to WUS. Sausages were stored by 60 days and physico-chemical and microbiological parameters were evaluated. US treatment inhibited the growth of psychrotrophic and lactic bacteria, reduced the lipid oxidation and promoted little pH and texture modifications during storage, improving the pasteurization. However, no information are available about the possible generation of toxic substances after US processing and further investigations must be carried out before the industrial scale-up of the process. An improvement on the effect of pasteurization of packaged sausages could be obtained by the use of ultrasound, reducing the time and the temperature used in conventional process and improving the shelf life of product without changes in its physical and chemical characteristics. The adaptation of the proposed process is relatively simple to be performed in conventional equipment used in industry and has potential for continuous processing and scale up. Because no information are available about the possible generation of toxic substances after the US processing, further investigations must be carried out before the industrial scale-up of the process.

Hot Water Shrinkage as a Post-Lethal Intervention against L isteria Monocytogenes : Preliminary Assessment in a Turkey-Based Virginia Ham Model

This preliminary laboratory trial evaluated the potential of hot water shrinkage to reduce post-lethal surface contamination by Listeria monocytogenes (Lm) in a turkey-based Virginia ham model. We inoculated triplicate of ham slices (10 cm2, 2-cm thick) with 105 cfu/cm2 of Lm (ATCC 19114). Subsequently, they were vacuum-packaged and placed in a thermostated water bath at 75, 80, 85 and 90C for 0, 20, 25 and 30 s. Treatment at 75–85C for up to 30 s did not affect Lm survival, while nearly 4-log reduction was observed at 90C for 30 s. The strong correlation (r = 0.9685–0.9891) between results and estimated lethalities (from previous inactivation data) highlights the potential of the 90C/30 s regimen as an effective post-lethal intervention. However, these results should be used with caution as they may vary under different industry conditions. Further research is needed to develop an appropriate pathogen reduction model for this process. Practical Applications Hot water shrinkage has a promising application in controlling post-lethal surface contamination by Listeria monocytogenes in some deli meats. This intervention is likely to be cheaper than regular post-package pasteurization. It is also feasible, from a productivity standpoint, in many medium-sized companies. The latter may work only for products with a smooth surface and a composition similar to that of the turkey-based Virginia ham tested in this study.

Effect of a post-packaging pasteurization process on inactivation of a Listeria innocua surrogate in meat products

Effects of surface pasteurization on inactivation of Listeria innocua were investigated. Surface temperature, monitored during post-packaging pasteurization, was used to predict the lethality of L. monocytogenes. Temperatures reached 70°C for lean and fat sausages within 9 min of treatment. An inoculation study validated the efficacy of post-processing and the thermal lethality of L. monocytogenes. Pre-cooked sausage and ham, inoculated with approximately 107 CFU/cm2 of L. innocua, were heated to a surface temperature of 70°C. Numbers of L. innocua were reduced by 7 log on surface-inoculated sausage. Guidelines for safe, ready-to-eat meat products are provided for small scale meat processors.

Determination of 5-Log Reduction Times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in Acidified Foods with pH 3.5 or 3.8†

A critical factor in ensuring the safety of acidified foods is the establishment of a thermal process that assures the destruction of acid-resistant vegetative pathogenic and spoilage bacteria. For acidified foods such as dressings and mayonnaises with pH values of 3.5 or higher, the high water phase acidity (acetic acid of 1.5 to 2.5% or higher) can contribute to lethality, but there is a lack of data showing how the use of common ingredients such as acetic acid and preservatives, alone or in combination, can result in a 5-log reduction for strains of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in the absence of a postpackaging pasteurization step. In this study, we determined the times needed at 10°C to achieve a 5-log reduction of E. coli O157:H7, S. enterica, and L. monocytogenes in pickling brines with a variety of acetic and benzoic acid combinations at pH 3.5 and 3.8. Evaluation of 15 different acid-pH combinations confirmed that strains of E. coli O157:H7 were significantly more acid resistant than strains of S. enterica and L. monocytogenes. Among the acid conditions tested, holding times of 4 days or less could achieve a 5-log reduction for vegetative pathogens at pH 3.5 with 2.5% acetic acid or at pH 3.8 with 2.5% acetic acid containing 0.1% benzoic acid. These data indicate the efficacy of benzoic acid for reducing the time necessary to achieve a 5-log reduction in target pathogens and may be useful for supporting process filings and the determination of critical controls for the manufacture of acidified foods.

Study of the effect of post-packaging pasteurization and argon modified atmosphere packaging on the sensory quality and growth of endogenous microflora of a sliced cooked meat product

The objective of this work was to study the effect of post-packaging pasteurization on the sensory quality and growth of natural microorganisms during refrigerated storage (6 °C) of a cooked meat product considering two packaging atmospheres based on mixture of typical gases (CO(2)/N(2) (22/78%) and novel gases (CO(2)/Ar (17/83%)). Growth of lactic acid bacteria was significantly different between samples with and without post-packaging pasteurization, showing a growth rate >0.44 and equal to 0.28 log cfu/day, respectively. For samples with post-packaging pasteurization, atmosphere CO(2)/Ar resulted in a lower growth of lactic acid bacteria and a better sensory quality. Overall, samples without post-packaging pasteurization did not show a significant reduction of sensory quality during storage time (121 days) while samples with post-packaging pasteurization showed deterioration in their sensory quality. Further investigation is needed to obtain more definitive conclusions about the effect of post-packaging pasteurization and argon-based packaging atmospheres on cooked meat products.

Effect of High-Pressure Post-Packaging Pasteurization on Microbiological Quality of Ready-to-Use Vegetables

This study was designed to estimate the potential use of high-pressure processing as a post-lethality treatment for inactivating Listeria monocytogenes, Staphyloccoccus aureus and Salmonella Typhimurium in vacuum-packed ready-to-use vegetables. The ready-to-use vegetable samples were subjected to 500 MPa for 0, 5, 10, 20 and 30 min. The numbers of L. monocytogenes and S. aureus in bean sprout and spinach treated at 500 MPa still remained at the detectable level of 1.3 log cfu/g. The numbers of S. Typhimurium in balloon flower root, bean sprout, bracken, carrot, cucumber, radish, mushroom and spinach were reduced to below the detection limit after a 10-min pressure holding time. The Weibull model provided a better fit at all survival curves (n < 1) of L. monocytogenes, S. aureus and S. Typhimurium. Therefore, the results provide practical information on using high-pressure processing as an effective post-packaging intervention technology for ensuring microbiological safety of ready-to-use vegetables. Practical Applications High pressure effectively decreased the numbers of Listeria monocytogenes, Staphyloccoccus aureus and Salmonella Typhimurium inoculated in ready-to-use vegetables during the pressure come-up time and holding time. Therefore, high-pressure processing can be used as a post-packaging pasteurization treatment for inactivating foodborne pathogen contaminated in ready-to-use vegetables.

A predictive model for the inactivation of Listeria innocua in cooked poultry products during postpackage pasteurization.

Contamination of Listeria monocytogenes in ready-to-eat poultry products poses potential risk of listeriosis to the public. To control the level of Listeria contamination, attention has been focused on the postpackage pasteurization of fully cooked poultry products. In this study, we sought to develop a model to predict the thermal inactivation of L. monocytogenes in chicken drumettes during postpackage hot water pasteurization. Fully cooked chicken drumettes were inoculated with Listeria innocua as a surrogate microorganism for Listeria monocytogenes, vacuum packaged, and treated in hot water baths at 60, 70, 80, and 90°C for different heating times. Experimental results showed that a 7-log CFU/g reduction of L. innocua occurred at 54, 28, 18, and 10 min at 60, 70, 80, and 90°C, respectively. The Weibull model was used to fit the survival curves of L. innocua at each heating temperature. The root mean square errors and residual plots indicated good agreements between the predicted and observed values. The predictive model was further validated by predicting a new data set generated in the pilot-plant tests. Model performance was evaluated by the acceptable prediction zone method, and the results indicated that the percentages of acceptable prediction errors were 100, 100, 82.4, and 87.5% at 60, 70, 80 and 90°C, respectively, which were all greater than the threshold acceptable value of 70% , indicating good performance of the model. The developed predictive model can be used as a tool to predict thermal inactivation behaviors of L. monocytogenes in ready-to-eat chicken drumettes products.

HIGH PRESSURE PROCESSING INACTIVATION OFLISTERIA INNOCUAIN MINCED TROUT (ONCORHYNCHUS MYKISS)

ABSTRACT High pressure processing is a food pasteurization process with the potential to kill microorganisms with minimal effects on the sensory quality and nutrient content of the food. The effectiveness of HPP for inactivating Listeria innocua in a muscle food model system consisting of minced trout (Oncorhynchus mykiss) at different salt levels (0, 1, or 3% added NaCl), and the resultant visual changes to the mince using scanning electron microscopy (SEM) was examined. A three-strain cocktail of the pathogen surrogate L. innocua (ca. 108–109 cfu/g) was inoculated into fish samples, which were treated at eight pressures in the range of 150–517 MPa at 20C. Treatment at ≥414 MPa for 5 min achieved greater than a 4-log reduction for the Listeria strains tested. Adding salt increased the effectiveness of pressure treatment for the 414 MPa and 517 MPa treatments by an additional 2.5-log. SEM revealed evidence of cell wall deformation and collapse in pressure-treated samples, particularly at 414 and 517 MPa. This study indicates that HPP treatment could potentially be an effective nonthermal pasteurization method for certain types of cured fish products. PRACTICAL APPLICATIONS High pressure processing (HHP) was examined as an alternative to thermal post-packaging pasteurization for Listeria sp. control which often causes softening and loss of flavor and color in ready-to-eat cured and smoked aquatic foods. Adding salt to cured minced trout (1 or 3% by weight) increased the inactivation of Listeria sp. during HHP processing (150–517 MPa at 20C, 5 min). Four-log or higher reductions at or above 414 MPa were possible. Effective pasteurization processes resulted in toughening, but this may be desirable in formed fish products and jerkies made from fish such as trout, chum or pink salmon where the muscle tends to be soft. Pressure treatment may reduce the need for phosphate additives in minced fish yielding a “cleaner” (no additives) label statement. Improving texture during pasteurization could increase the utilization of muscle from frames and smaller fish in higher value food items.

Effect of Inhibitory Extracts Derived from Liquid Smoke Combined with Postprocess Pasteurization for Control of Listeria monocytogenes on Ready-to-Eat Meats

Surface pasteurization was examined in combination with low-phenolic antimicrobial extracts derived from liquid smoke to inhibit and prevent the growth of Listeria monocytogenes during the shelf life of ready-to-eat meats. In preliminary trials with retail frankfurters, one smoke derivative (2-min dip) produced a 0.3-log reduction of L. monocytogenes and a 1-min inbag pasteurization (73.9°C) produced a 2.9-log reduction, whereas a combination of the two treatments produced a 5.3-log reduction that resulted in no detectable Listeria by week 3 under accelerated shelf-life conditions (10°C). In trials with frankfurters manufactured without lactate or diacetate that were treated with a shortened 1-s dip, this smoke extract and one with reduced smoke flavor and color both produced a >4.5-log reduction of L. monocytogenes on frankfurters when heated at 73.9°C for 1 min, with no recoverable Listeria detected for 10 weeks when stored at 6.1°C. When deli turkey breast chubs manufactured without lactate, diacetate, or nitrite were treated with a 1-s dip in combination with radiant-heat pasteurization (270°C), growth of L. monocytogenes was retarded but not prevented. However, in a similar study in which smoke extract treatment of deli turkey breast was combined with in-bag postpackage pasteurization (water submersion at 93.3°C), a 60-, 45-, or even 30-s heat treatment resulted in a 2- to 3-log reduction of L. monocytogenes, with no growth on the meat during 10 weeks of storage at 6.1°C. These findings indicate that reduced-acid low-phenolic antimicrobial liquid smoke derivatives combined with surface pasteurization are capable of reducing or preventing growth of L. monocytogenes to meet the criteria for the U.S. Department of Agriculture Food Safety and Inspection Service Alternative 1 process for ready-to-eat deli meat products manufactured without lactate or diacetate.

Microbial heat resistance of Listeria monocytogenes and the impact on ready-to-eat meat quality after post-package pasteurization

Several methods using bactericides, hydrostatic pressure, and post-package pasteurization technologies to control Listeria monocytogenes (LM) in ready-to-eat meats have been attempted. In addition to controlling LM contamination, any newly developed technology must have minimal effects on organoleptic properties. The objectives of this study were to: (1) determine the heat resistance of LM in two brands (A and B) of bologna differing in formulations, and, (2) evaluate the effects of post-package pasteurization on product quality. Fat content did not affect LM heat resistance in bologna at 55, 60, and 65 °C; however, Brand B bologna had a numerically lower inactivation rate. Microbial heat resistance differed ( P < 0.05) with changes in pasteurization temperature. Time and temperature affected ( P < 0.05) cook-loss and L ∗ Hunter color value for both bologna brands. These data show that post-package pasteurization is effective but suggest that meat formulations may need modification to prevent development of negative quality characteristics.

Evaluation of Small-Scale Hot-Water Postpackaging Pasteurization Treatments for Destruction of Listeria monocytogenes on Ready-to-Eat Beef Snack Sticks and Natural-Casing Wieners

This study was conducted to evaluate small-scale hot-water postpackaging pasteurization (PPP) as a postlethality (post-cooking) treatment for Listeria monocytogenes on ready-to-eat beef snack sticks and natural-casing wieners. Using a commercially available plastic packaging film specifically designed for PPP applications and 2.8 liters of boiling water (100°C) in a sauce pan on a hot plate, an average reduction in L. monocytogenes numbers of ≥2 log units was obtained using heating times of 1.0 min for individually packaged beef snack sticks (three brands) and 4.0 min for packages of four sticks (two brands) and seven sticks (three brands). Average product surface temperatures, measured as soon as possible after PPP and opening the package, were 47 to 51.5, 58 to 61.5, and 58.5 to 61°C for the beef snack sticks packages of one, four, and seven sticks per package, respectively. A treatment of 7.0 min for packages of four natural-casing wieners (three brands) achieved L. monocytogenes reductions of ≥1.0 log unit and average product surface temperature of 60.5 to 63.5°C. Cooked-out fat and moisture resulting from tested treatments ranged from 0.2 to 1.1% by weight for beef snack sticks and from 0.4 to 1.2% by weight for natural-casing wieners. For natural-casing wieners, PPP had no detrimental effect on overall product desirability to consumers; results suggested that PPP may significantly enhance appearance of this product. However, for beef snack sticks the cooking out of fat and moisture during PPP had a significant negative effect on consumer opinions of product appearance.

Effect of Prepackage and Postpackage Pasteurization on Postprocess Elimination of Listeria monocytogenes on Deli Turkey Products

Surface pasteurization for inactivation of Listeria monocytogenes was evaluated for radiant heat prepackage pasteurization, submersed water postpackage pasteurization, and combinations of the two techniques on various types of ready-to-eat deli turkey products obtained from at least four different manufacturers. Products were inoculated either by in-package liquid inoculum or surface sponge-contact with approximately 109 CFU of L. monocytogenes. Additional testing of radiant heat pasteurization was performed with low-level inoculation of product undersides with approximately 100 CFU of L. monocytogenes followed by enrichment recovery after pasteurization. Prepackage pasteurization provided 2.0 to 2.8 log reductions when processed for 60 s and 2.8 to 3.8 log reductions when processed for 75 s. An improved radiant oven provided 3.53 (60 s) and 4.76 (75 s) log reductions of L. monocytogenes. No positive samples were detected after enrichment when 40 samples of deli turkey (4 to 4.5 kg) undersides were inoculated at low levels and processed for 75 s. Submersed water postpackage pasteurization provided 1.95 to 3.0 log reductions when processed for 2, 3, 4, or 5 min, and combinations of the two processes gave 3.0 to 4.0 log inactivation of L. monocytogenes using either 60 + 60 s or 60 + 90 s for the prepackage and postpackage pasteurization processes, respectively. These processes, either individually or in combination, can provide postprocess elimination of bacteria for the manufacture of safe ready-to-eat deli meats.

Inactivation of Listeria innocua in Nisin-Treated Salmon (Oncorhynchus keta) and Sturgeon (Acipenser transmontanus) Caviar Heated by Radio Frequency

Recent regulatory concerns about the presence of the pathogen Listeria monocytogenes in ready-to-eat aquatic foods such as caviar has prompted the development of postpackaging pasteurization processes. However, caviar is heat labile, and conventional pasteurization processes affect the texture, color, and flavor of these foods negatively. In this study, chum salmon (Oncorhynchus keta, 2.5% total salt) caviar or ikura and sturgeon (Acipenser transmontanus, 3.5% total salt) caviar were inoculated with three strains of Listeria innocua in stationary phase at a level of more than 107 CFU/g. L. innocua strains were used because they exhibit an equivalent response to L. monocytogenes for many physicochemical processing treatments, including heat treatment. The products were treated by immersion in 500 IU/ml nisin solution and heat processed (an 8-D process without nisin or a 4-D process with 500 IU/ml nisin) in a newly developed radio frequency (RF; 27 MHz) heating method at 60, 63, and 65°C. RF heating along with nisin acted synergistically to inactivate L. innocua cells and total mesophilic microorganisms. In the RF–nisin treatment at 65°C, no surviving L. innocua microbes were recovered in sturgeon caviar or ikura. The come-up times in the RF-heated product were significantly lower compared with the water bath–heated caviar at all treatment temperatures. The visual quality of the caviar products treated by RF with or without nisin was comparable to the untreated control.

Prepackage Surface Pasteurization of Ready-to-Eat Meats with a Radiant Heat Oven for Reduction of Listeria monocytogenes

In this paper, a thermal process for the surface pasteurization of ready-to-eat (RTE) meat products for the reduction of Listeria monocytogenes on such products (turkey bologna, roast beef, corned beef, and ham) is described. The process involves the passage of products through a “tunnel” of heated coils on a stainless steel conveyor belt at various treatment times relevant to the manufacture of processed meat for the surface pasteurization of RTE meat products. Two inoculation procedures, dip and contact inoculation, were examined with the use of a four-strain cocktail of L. monocytogenes prior to heat processing. With the use of radiant heat prepackage surface pasteurization, 1.25 to 3.5-log reductions of L. monocytogenes were achieved with treatment times of 60 to 120 s and air temperatures of 475 to 750°F (246 to 399°C) for these various RTE meats. Reduction levels differed depending on the type of inoculation method used, the type of product used, the treatment temperature, and the treatment time. Prepackage pasteurization (60 s) was also combined with postpackage submerged water pasteurization for formed ham (60 or 90 s), turkey bologna (45 or 60 s), and roast beef (60 or 90 s), resulting in reductions of 3.2 to 3.9, 2.7 to 4.3, and 2.0 to 3.75 log cycles, respectively. These findings demonstrate that prepackage pasteurization, either alone or in combination with postpackage pasteurization, is an effective tool for controlling L. monocytogenes surface contamination that may result from in-house handling.

Postpackage Pasteurization of Ready-to-Eat Deli Meats by Submersion Heating for Reduction of Listeria monocytogenes

A mixed cocktail of four strains of Listeria monocytogenes was resuspended in product purge and added to a variety of ready-to-eat (RTE) meat products, including turkey, ham, and roast beef. All products were vacuum sealed in shrink-wrap packaging bags, massaged to ensure inoculum distribution, and processed by submersion heating in a precision-controlled steam-injected water bath. Products were run in pairs at various time-temperature combinations in either duplicate or triplicate replications. On various L. monocytogenes–inoculated RTE deli meats, we were able to achieve 2- to 4-log cycle reductions when processed at 195°F (90.6°C), 200°F (93.3°C), or 205°F (96.1°C) when heated from 2 to 10 min. High-level inoculation with L. monocytogenes (~107 CFU/ml) ensured that cells infiltrated the least processed surface areas, such as surface cuts, folds, grooves, and skin. D- and z-value determinations were made for the Listeria cocktail resuspended in product purge of each of the three meat categories. However, reduction of L. monocytogenes in product challenge studies showed much less reduction than was observed during the decimal reduction assays and was attributed to a combination of surface phenomena, including surface imperfections, that may shield bacteria from the heat and the migration of chilled purge to the product surface. The current data indicate that minimal heating regimens of 2 min at 195 to 205°F can readily provide 2-log reductions in most RTE deli meats we processed and suggest that this process may be an effective microbial intervention against L. monocytogenes on RTE deli-style meats.