High pressure processing to control Salmonella in raw pet food without compromising the freshness appearance: The impact of acidulation and frozen storage.

The trend of feeding dogs and cats with raw pet food claiming health benefits poses health concerns due to the occurrence of pathogenic bacteria. High pressure processing (HPP) allows the non-thermal inactivation of microorganisms, preserving the nutritional characteristics with minimal impact on organoleptic traits of food. The present study aimed to evaluate and model the effect of HPP application (450-750 MPa for 0-7 min) on the inactivation of Salmonella, endogenous microbiota and colour of raw pet food formulated with different concentrations of lactic acid (0-7.2 g/kg) as natural antimicrobial. Additionally, the effect of a subsequent frozen storage of pressurized product was assessed. Salmonella inactivation ranged between 1 and 9 log, depending on the combination of conditions. According to the polynomial model obtained, the effect of pressure was linear, while a quadratic term was also included for holding time (depicting the occurrence of a resistant tail at ca. 4-6 min). The effect of lactic acid was dependent on the pressure level, being most relevant for treatments below 600 MPa. Frozen storage after HPP prevented the pathogen recovery and caused a further Salmonella inactivation enhanced by lactic acid in most of the treatments. Endogenous microbial groups were significantly reduced by HPP to below the detection level in several conditions. In general, little effect of HPP on the instrumental colour parameters was observed, except for a slight increase in lightness, which was hardly appreciable from visual observation. High pressure processing emerges as a relevant technology for the control of Salmonella spp. and to manage the microbiological safety of raw pet food. The mathematical model can be used as decision support tool to design safer raw pet food, while keeping the desired freshness appearance of the products.

Enhanced high hydrostatic pressure lethality in acidulated raw pet food formulations was pathogen species and strain dependent.

Feeding dogs and cats with raw meat-based pet food is taking relevance in the recent years. The high aw of these products together with the no cooking before its consumption by the animal pose a risk due to the potential occurrence and growth of foodborne pathogens. High pressure processing (HPP) is a non-thermal emerging technology that can be used as a lethality treatment to inactivate microorganisms with a minimum impact on the sensory and nutritional traits of the product. The purpose of the present study was to evaluate the variability in pressure resistance of different strains of the relevant foodborne pathogens Salmonella spp., Escherichia coli and Listeria monocytogenes in raw pet food formulated without and with lactic acid. In general, Salmonella and L.monocytogenes strains showed a higher resistance to HPP than E. coli strains. In lactic acid acidulated formulations, the susceptibility to HPP of L. monocytogenes was markedly enhanced. The resistance to HPP was not only dependent on the microorganism but also on the strain. Thus, the selection of the proper strains should be taken into account when designing and validating the application of HPP as a control measure within the HACCP plan.

Modelling the piezo-protection effect exerted by lactate on the high pressure resistance of Listeria monocytogenes in cooked ham.

Food safety is often based on the application of several preservative (hurdle) factors whose combination must be smartly selected. The aim of the present study was to evaluate the effect of lactate and diacetate on the high pressure processing (HPP) inactivation of three L. monocytogenes strains (CTC1011, CTC1034 and Scott A) in sliced cooked ham. Inoculated vacuum-packed slices of cooked ham formulated without organic acids and with lactate, diacetate or the combination of both were pressurized at 400 MPa for different holding times and the inactivation kinetics were characterised by fitting primary and secondary models. The shape of the inactivation curves for L. monocytogenes depended on both product formulation and strain. Interestingly, lactate caused a dose-dependent piezo-protection in all three strains, as the HPP inactivation rate decreased in cooked ham formulated with increasing amounts of lactate and in comparison with the control product. The design, validation and implementation of HPP requires a tailor-made approach, considering product formulation and selection of strain/s.

Risk management tool to define a corrective storage to enhance Salmonella inactivation in dry fermented sausages.

The resistance of Salmonella to the harsh conditions occurring in shelf-stable dry fermented sausages (DFS) poses a food safety challenge for producers. The present study aimed to model the behaviour of Salmonella in acid (with starter culture) and low-acid (without starter culture) DFS as a function of aw and storage temperature in order to build a decision supporting tool supporting the design of a corrective storage strategy to enhance the safety of DFS. Salmonella spp. were inoculated in the raw meat batter at ca. 6 Log cfu/g with a cocktail of 3 strains (CTC1003, CTC1022 and CTC1754) just before mixing with the other ingredients and additives. After stuffing, sausages were fermented and ripened following industrial processing conditions. Different drying-times were applied to obtain three batches with different aw (0.88, 0.90 and 0.93). Afterwards, DFS were stored at 4, 8, 15 and 25 °C for a maximum of three months and Salmonella spp. were periodically enumerated. The Weibull model was fitted to Log counts data to estimate inactivation kinetic parameters. The impact of temperature and aw on the primary inactivation parameters was evaluated using a polynomial equation. The results of the challenge tests showed that Salmonella spp. levels decreased during storage at all the assayed conditions, from 0.8 Log (in low-acid DFS at 4 °C) up to 6.5 Log (in acid DFS at 25 °C). The effect of both aw and temperature was statistically significant. Delta (δ) parameter decreased by decreasing aw and increasing temperature, while the shape (p) parameter ranged from above 1 (concave) at 10 °C to below 1 at 25 °C (convex). A common secondary model for the p parameter was obtained for each type of DFS, acid and low-acid, indicating that acidification during the production of DFS affected the time for the first Log reduction (δ) during the subsequent storage, but not the overall shape (p parameter) of the inactivation. The developed models covered representative of real conditions, such as Salmonella contamination in the raw materials and its adaptation to the harsh processing conditions. The good predictive performance shown when applying the models to independent data (i.e. up to 80% of the predictions within the 'Acceptable Simulation Zone' for acid sausages) makes them a suitable and reliable risk management tool to support manufacturers to assess and design a lethality treatment (i.e. corrective storage) to enhance the Salmonella inactivation in the product before DFS are released to the market.

Modeling and designing a Listeria monocytogenes control strategy for dry-cured ham taking advantage of water activity and storage temperature.

Dry-cured ham is a shelf-stable product that can be contaminated with Listeria monocytogenes due to post-processing operations, compromising the compliance of zero tolerance policies (e.g. US Listeria rule). The present study quantifies the behavior of L. monocytogenes in sliced Spanish dry-cured ham of different water activity (aw) during storage at different temperatures. Inactivation kinetics were estimated by fitting primary models to the experimental data. The effect of temperature and aw on kinetic parameters was characterized through secondary polynomial models. L. monocytogenes viability decreased in all the assayed conditions, confirming that dry-cured ham is not only listeriostatic but listericidal. The fastest and highest reductions were observed at 25 °C, with 1 Log reduction after 6 and 9 days in Iberian and Serrano ham respectively. The work provides scientifically-based data and models to design a low-cost control measure based on a corrective storage as a post-lethality treatment to enhance the accomplishment of zero-tolerance requirements.

Domestic refrigerator temperatures in Spain: Assessment of its impact on the safety and shelf-life of cooked meat products.

Temperature is one of the main factors governing the growth of microorganisms. The aim of the present study was to provide temperature conditions representative of the food products stored in domestic refrigerators and to assess the impact of the temperature (fluctuation) on the shelf-life of refrigerated cooked meat products, from the safety and the spoilage point of view. The analysis of the time-temperature profiles recorded from 160 domestic refrigerators of households from small (28%) and large (72%) municipalities in Catalonia (Spain) showed that the 24 h-mean temperature could be described by a normal distribution (mean = 5.4 °C, standard deviation = 2.3 °C) with a mean value within the upper limit of the appropriate storage temperature of refrigerated products (i.e. ≤6 °C). The impact of door openings or day and night was not significant. Temperature distribution showed differences depending on the season, being higher in the cold season than in the warm one. Noteworthy, refrigerators of elderly (≥ 65 years old) households showed a higher percentage of time at temperatures >8 °C in comparison with those of the general population. Overall, the 75th percentile of the distribution of the 24 h-mean temperature values was 6.7 °C. This study can be used as a scientific evidence of the consumer storage stage when food business operators or laboratories conduct shelf-life studies. According to the simulation of the growth of Listeria monocytogenes and lactic acid bacteria in cooked meat products, risk scenarios were identified in which the critical level of the pathogen could be reached before lactic acid bacteria achieved the spoilage level. The fluctuation of the refrigerator temperature ranged from 0.5 up to 12.2 °C within the 24 h-profile. The assessment of the safety of cooked meat products stored at constant temperature or under different time-temperature profiles showed that both the mean and the fluctuation of the profile had an impact on the shelf-life, which was higher at low temperatures. The improvement of the household refrigerated storage would be an effective way to increase food safety of refrigerated ready-to-eat food.

Assessment of the bioprotective potential of lactic acid bacteria against Listeria monocytogenes on vacuum-packed cold-smoked salmon stored at 8 °C.

Smoked salmon is a highly appreciated delicatessen product. Nevertheless, this ready-to-eat (RTE) product is considered at risk for Listeria monocytogenes, due to both the prevalence and growth potential of this bacteria on the product. Biopreservation may be considered a mild and natural effective strategy for minimizing this risk. In this study, we evaluated the following three potential bioprotective lactic acid bacterial strains against L. monocytogenes in three smoked salmon types with different physicochemical characteristics, primarily fat, moisture, phenol and acid acetic content: two bacteriocin-like producers that were isolated from smoked salmon and identified as Lactobacillus curvatus and Carnobacterium maltaromaticum and a recognized bioprotective bacteriocin producer from meat origin, Lactobacillus sakei CTC494. L. sakei CTC494 inhibited the growth of L. monocytogenes after 21 days of storage at 8 °C in all the products tested, whereas L. curvatus CTC1742 only limited the growth of the pathogen (<2 log increase). The effectiveness of C. maltaromaticum CTC1741 was dependent on the product type; this strain limited the growth of the pathogen in only one smoked salmon type. These results suggest that the meat-borne starter culture, L. sakei CTC494, may potentially be used as a bioprotective culture to improve the food safety of cold-smoked salmon.

New insights on Listeria monocytogenes growth in pressurised cooked ham: A piezo-stimulation effect enhanced by organic acids during storage.

The aim of the present study was to understand growth and survival responses of Listeria monocytogenes during the storage of high pressure processed (HPP) cooked ham formulated with organic acids to inhibit growth of the pathogen. Cooked ham batches were manufactured without organic acids (control), with potassium lactate (2.8% or 4%) or with potassium lactate and sodium diacetate (2.0% + 0.11% or 2.0% + 0.45%). Products were aseptically sliced and inoculated with 107 cfu/g or 102 cfu/g of either L. monocytogenes CTC1034 (a meat isolate) or a cocktail of three isolates (12MOB045Lm, 12MOB089Lm and Scott A). Vacuum-packed samples with 107 cfu/g were HPP at 600 MPa for 3 min, whereas samples with 102 cfu/g were not HPP. Growth or survival of L. monocytogenes was determined during subsequent storage at 8, 12 and 20 °C. Growth or survival was characterized by fitting the experimental data using the primary logistic model and the log-linear with shoulder model, respectively. Secondary models were fitted to characterize the effect of temperature on growth kinetic parameters without or with HPP. For cooked ham without organic acids, growth rates of L. monocytogenes were slightly increased by HPP and lag times were longer. Interestingly, for cooked ham with organic acids, the HPP had a significant stimulating effect on subsequent growth of L. monocytogenes (piezo-stimulation). At 20 °C, the growth rates of L. monocytogenes in cooked ham with lactate were up to 4-fold higher than those of the same product without HPP. The observed enhancement of the piezo-stimulating effect of organic acids on growth rates during storage of HPP cooked ham represents a challenge for the use of organic acids as antimicrobials in these products. A predictive model available as part of the Food Spoilage and Safety Predictor (FSSP) software seemed useful to predict growth and growth boundary of L. monocytogenes in non-pressurised cooked ham. This model was calibrated to take into account the observed piezo-stimulating effect and to predict growth of L. monocytogenes in HPP cooked ham with organic acids.

Diversity and distribution of Listeria monocytogenes in meat processing plants.

Listeria monocytogenes is a major concern for the meat processing industry because many listeriosis outbreaks have been linked to meat product consumption. The aim of this study was to elucidate L. monocytogenes diversity and distribution across different Spanish meat processing plants. L. monocytogenes isolates (N = 106) collected from food contact surfaces of meat processing plants and meat products were serotyped and then characterised by multilocus sequence typing (MLST). The isolates were serotyped as 1/2a (36.8%), 1/2c (34%), 1/2b (17.9%) and 4b (11.3%). MLST identified ST9 as the most predominant allelic profile (33% of isolates) followed by ST121 (16%), both of which were detected from several processing plants and meat products sampled in different years, suggesting that those STs are highly adapted to the meat processing environment. Food contact surfaces during processing were established as an important source of L. monocytogenes in meat products because the same STs were obtained in isolates recovered from surfaces and products. L. monocytogenes was recovered after cleaning and disinfection procedures in two processing plants, highlighting the importance of thorough cleaning and disinfection procedures. Epidemic clone (EC) marker ECI was identified in 8.5%, ECIII was identified in 2.8%, and ECV was identified in 7.5% of the 106 isolates. Furthermore, a selection of presumably unrelated ST9 isolates was analysed by multi-virulence-locus sequence typing (MVLST). Most ST9 isolates had the same virulence type (VT11), confirming the clonal origin of ST9 isolates; however, one ST9 isolate was assigned to a new VT (VT95). Consequently, MLST is a reliable tool for identification of contamination routes and niches in processing plants, and MVLST clearly differentiates EC strains, which both contribute to the improvement of L. monocytogenes control programs in the meat industry.

The potential probiotic Lactobacillus rhamnosus CTC1679 survives the passage through the gastrointestinal tract and its use as starter culture results in safe nutritionally enhanced fermented sausages.

The human-derived potential probiotic strain Lactobacillus rhamnosus CTC1679 was used as a starter culture in reduced fat and sodium low-acid fermented sausages (fuets) to assess its ability to survive through the gastrointestinal tract (GIT) in a human intervention study consisting of 5 healthy volunteers who consumed 25 g fuet a day for 21 days. Faecal samples were analysed during and after consumption. L. rhamnosus CTC1679 produced a transient colonisation of the human GIT and persisted during the ingestion period of fuet containing L. rhamnosus CTC1679 at levels ca. 8log CFU/g. After 3 days of non-consumption, the strain was still recovered in the faeces of all the volunteers. To evaluate the safety of the nutritionally enhanced manufactured fuets, a challenge test was designed in a separately manufactured batch. L. rhamnosus CTC1679 was able to grow, survive and dominate (levels ca. 10(8) CFU/g) the endogenous lactic acid bacteria (LAB), prevented the growth of Listeria monocytogenes throughout the whole ripening process of the fuets and eliminated Salmonella. After 35 days of storage at 4 °C, L. monocytogenes was not detected, achieving absence in 25 g of the product. The application of high hydrostatic pressure (HHP) treatment (600 MPa for 5 min) at the end of ripening (day 14) produced an immediate reduction of L. monocytogenes to levels <1log CFU/g. After 35 days of storage at 4 °C the pathogen was not detected. Thus, the strain L. rhamnosus CTC1679 is a suitable starter culture for producing safe potentially probiotic fermented sausages.

Nutritionally enhanced fermented sausages as a vehicle for potential probiotic lactobacilli delivery.

The suitability of three potential probiotic lactobacilli strains (Lactobacillus casei CTC1677, L. casei CTC1678 and Lactobacillus rhamnosus CTC1679), previously isolated from infants' faeces and characterized, and three commercial probiotic strains (Lactobacillus plantarum 299v, L. rhamnosus GG and L. casei Shirota) was assessed during the manufacture of low-acid fermented sausages (fuets) with reduced Na(+) and fat content. The inoculated strains were successfully monitored by RAPD-PCR during the process. L. rhamnosus CTC1679 was the only strain able to grow and dominate (levels ca. 10(8)CFU/g) the endogenous lactic acid bacteria population in two independent trials, throughout the ripening process. Thus, fuet containing L. rhamnosus CTC1679 as a starter culture could be a suitable vehicle for putative probiotic bacteria delivery. All the final products recorded a satisfactory overall sensory quality without any noticeable off-flavour, and with the characteristic sensory properties of low-acid fermented sausages.

Characterization of lactic acid bacteria isolated from infant faeces as potential probiotic starter cultures for fermented sausages.

A total of 109 lactic acid bacteria isolated from infant faeces were identified by partial 16S rRNA, cpn60 and/or pheS sequencing. Lactobacillus was the most prevalent genus, representing 48% of the isolates followed by Enterococcus (38%). Lactobacillus gasseri (21%) and Enterococcus faecalis (38%) were the main species detected. A further selection of potential probiotic starter cultures for fermented sausages focused on Lactobacillus as the most technologically relevant genus in this type of product. Lactobacilli strains were evaluated for their ability to grow in vitro in the processing conditions of fermented sausages and for their functional and safety properties, including antagonistic activity against foodborne pathogens, survival from gastrointestinal tract conditions (acidity, bile and pancreatin), tyramine production, antibiotic susceptibility and aggregation capacity. The best strains according to the results obtained were Lactobacillus casei/paracasei CTC1677, L. casei/paracasei CTC1678, Lactobacillus rhamnosus CTC1679, L. gasseri CTC1700, L. gasseri CTC1704, Lactobacillus fermentum CTC1693. Those strains were further assayed as starter cultures in model sausages. L. casei/paracasei CTC1677, L. casei/paracasei CTC1678 and L. rhamnosus CTC1679 were able to lead the fermentation and dominate (levels ca. 10(8) CFU/g) the endogenous lactic acid bacteria, confirming their suitability as probiotic starter cultures.

Assessment of safe enterococci as bioprotective cultures in low-acid fermented sausages combined with high hydrostatic pressure.

Three bacteriocinogenic, non-aminogenic and non-virulent Enterococcus strains (Enterococcus faecium CTC8005, Enterococcus devriesei CTC8006 and Enterococcus casseliflavus CTC8003) were used as starter cultures in low-acid fermented sausages to assess their competitiveness and their bioprotective potential against Listeria monocytogenes and Staphylococcus aureus. The inoculated strains were successfully monitored by RAPD-PCR. All the strains were able to grow, survive and dominate the endogenous enterococci population and avoided the growth of Enterobacteriaceae. E. devriesei CTC8006 and E. faecium CTC8005 particularly inhibited the growth of L. monocytogenes during the whole ripening process. S. aureus was not affected by the inoculated bacteriocinogenic enterococci strains. The application of high hydrostatic pressure (HHP) treatment (600 MPa for 5 min) at the end of ripening (day 21) produced an immediate reduction in the counts of Enterobacteriaceae to levels <1 log cfu/g and promoted a decrease of 1-log unit in the counts of S. aureus. E. faecium CTC8005, which reduced the counts of L. monocytogenes ca. 2 log cfu/g immediately after stuffing and in combination with HHP treatment promoted a further reduction of 1 log cfu/g in the pathogen counts. The combination of E. faecium CTC8005 and HHP was the most efficient antilisterial approach.

High hydrostatic pressure and biopreservation of dry-cured ham to meet the Food Safety Objectives for Listeria monocytogenes.

This work aimed to evaluate the effect of nisin application (biopreservation) combined with high hydrostatic pressure processing (HHP) on the behavior of Listeria monocytogenes CTC1034 intentionally inoculated (at ca. 10(7)cells/g) onto the surface of ready-to-eat (RTE) sliced dry-cured ham. Two types of dry-cured ham, which had different water activities and fat contents were studied (a(w) of 0.92 and 14.25% fat and a(w) of 0.88 and 33.26% fat). Three batches were prepared for each type of product: (C) control, without nisin; (N) nisin directly applied (200 AU/cm(2)) and (F) nisin applied through active packaging, polyvinyl alcohol films with 200 AU/cm(2). Half of the samples were pressurized at 600 MPa for 5min. Counts of L. monocytogenes were periodically monitored throughout 60 days of storage at 8°C. The physico-chemical characteristics of the products enabled the survival of L. monocytogenes, but it was significantly reduced by the presence of nisin. The effect of biopreservation was greater when applied directly to the surface and in the product with lower water activity in comparison with the active packaging and the high water activity products, respectively. The immediate inactivation of L. monocytogenes by HHP ranged from 1.82 to 3.85 Log units, depending on the type of dry-cured ham. The lower the water activity, the less was the inactivation induced by HHP, both immediately and during storage. The reduction of L. monocytogenes immediately after HHP and during storage was more evident in batches with nisin applied directly to the surface of the product. The pathogen was not detected in some samples from day 5 of storage in the product with higher water activity. The effect of nisin applied through active packaging was lower than the direct application. The results of the present study indicated that HHP, as post-processing listericidal treatment, is more effective (both immediately and long term) than the use of nisin as an antimicrobial measure. However, the both hurdles combined (i.e. biopreservation and HHP) provided a wider margin of safety in the control of L. monocytogenes during the storage of RTE cured meat products.

The effect of NaCl-free processing and high pressure on the fate of Listeria monocytogenes and Salmonella on sliced smoked dry-cured ham.

NaCl is an important multifunctional ingredient applied in dry-cured ham elaboration. However, its excessive intake has been linked to serious cardiovascular diseases causing a recent increase in the development of reduced salt products. In the present study Listeria monocytogenes and Salmonella, food-borne pathogens which can cross-contaminate post processed products, were spiked with <100 CFU/g on slices of both standard (S) and NaCl-free processed (F) (elaborated with KCl+potassium lactate instead of NaCl) smoked dry-cured ham. Although L. monocytogenes and Salmonella counts decreased faster in S ham, pathogens were present in both types of non-pressure treated ham during the entire refrigerated storage period (112 days). Pressurisation at 600 MPa for 5 min caused the elimination of both pathogens in S ham after 14 days. In contrast, Salmonella and L. monocytogenes were present in F ham until days 28 and 56, respectively, indicating that the NaCl-free processed dry-cured ham had lower stability than standard smoked dry-cured ham.

Prevalence of Salmonella spp. and Listeria monocytogenes at small-scale spanish factories producing traditional fermented sausages.

The manufacturing of fermented sausages is subject to natural contamination processes that can potentially carry foodborne pathogens along the process chain and result in contamination of the final product. The aim of this study was to evaluate the occurrence of Salmonella spp. and Listeria monocytogenes at different sampling points during the manufacturing process of fuet, a type of traditional fermented sausage, at 10 small-scale Spanish factories. The presence of both pathogens was studied in the raw materials (19 casings and 19 meat batters), the final products (19 fermented sausages), and the factory equipment (12 mincing, 12 mixing, and 19 stuffing machines, 19 cutting tables, 11 knives, and 12 cold rooms) by using classical microbiological techniques and real-time PCR. Salmonella was not detected in the equipment analyzed or in the final products, but it was detected in the raw materials (23.7% of samples). L. monocytogenes showed higher incidence than Salmonella and was detected in the equipment (11.8% of samples), the raw materials (28.9%), and the final products (15.8%), confirming its ubiquity throughout the manufacturing process of fermented sausages. Five factories were further investigated to study the changes in the distribution of pathogens in the fuet production process over a period of either 2 or 3 years. There was considerable variation in the incidence of both pathogens at different sampling periods, and there was no relation between seasonal variations or geographic location of the factories.

Inactivation and recovery of Listeria monocytogenes, Salmonella enterica and Staphylococcus aureus after high hydrostatic pressure treatments up to 900 MPa.

High hydrostatic pressure (HP) processing is used in the food industry to enhance the safety and extend the shelf-life of food. Although a drastic decrease in microbial viability is achieved immediately after the application of HP treatments, under favorable conditions the injured bacteria can recover. The present study evaluated the inactivation and recovery of five strains of Listeria monocytogenes, Salmonella enterica and Staphylococcus aureus subjected to pressures of 400, 600, and 900 MPa under stressing and non-stressing conditions in a complex medium. Treatments at 400 and 600 MPa were found to greatly affect the viability of L. monocytogenes and S. enterica, but only a treatment of 5 min at 900 MPa decreased the levels of the three pathogens to below the detection limit (8-9 log units reduction). After HP treatment, not only the baroresistant S. aureus but also several replicates of L. monocytogenes and S. enterica strains recovered during subsequent incubation under favorable conditions. However, when HP was combined with low pH and nitrite but not with NaCl or lactate, the viability of pressurized S. aureus cells progressively decreased. As pathogenic bacteria can recover even after the application of very high pressure levels, the combination of HP with other hurdles for microbial growth, either intrinsically present in the food product or extrinsically applied, may be needed to guarantee the efficacy of technologies aimed at pathogen reduction and shelf-life extension.

Inactivation and recovery of Listeria monocytogenes, Salmonella enterica and Staphylococcus aureus after high hydrostatic pressure treatments up to 900 MPa

High hydrostatic pressure (HP) processing is used in the food industry to enhance the safety and extend the shelf-life of food. Although a drastic decrease in microbial viability is achieved immediately after the application of HP treatments, under favorable conditions the injured bacteria can recover. The present study evaluated the inactivation and recovery of five strains of Listeria monocytogenes, Salmonella enterica and Staphylococcus aureus subjected to pressures of 400, 600, and 900 MPa under stressing and non-stressing conditions in a complex medium. Treatments at 400 and 600 MPa were found to greatly affect the viability of L. monocytogenes and S. enterica, but only a treatment of 5 min at 900 MPa decreased the levels of the three pathogens to below the detection limit (8-9 log units reduction). After HP treatment, not only the baroresistant S. aureus but also several replicates of L. monocytogenes and S. enterica strains recovered during subsequent incubation under favorable conditions. However, when HP was combined with low pH and nitrite but not with NaCl or lactate, the viability of pressurized S. aureus cells progressively decreased. As pathogenic bacteria can recover even after the application of very high pressure levels, the combination of HP with other hurdles for microbial growth, either intrinsically present in the food product or extrinsically applied, may be needed to guarantee the efficacy of technologies aimed at pathogen reduction and shelf-life extension (AU)

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Combined effect of enterocin AS-48 and high hydrostatic pressure to control food-borne pathogens inoculated in low acid fermented sausages.

The single and combined effects of enterocin AS-48 and high hydrostatic pressure (HHP) on Listeria monocytogenes, Salmonellaenterica, and Staphylococcus aureus was investigated in fuet (a low acid fermented sausage) during ripening and storage at 7 degrees C or at room temperature. AS-48 (148 AU g(-1)) caused a drastic 5.5 log cfu g(-1) decrease in L. monocytogenes (P<0.001) and a significant (P<0.01) inhibition (1.79 logs) for Salmonella at the end of ripening (10 d). After pressurization (400 MPa) and storage Listeria counts remained below 5 cfu g(-1) in all fuets containing AS-48 (pressurized or not). HHP alone had no anti-Listeria effect. HHP treatment significantly reduced Salmonella counts, with lowest levels in pressurized fuets with AS-48. S. aureus showed similar growth for all treatments and storage conditions. These results indicate that AS-48 can be applied alone to control L. monocytogenes and combined with HHP treatment to control Salmonella in fuets.

Physical performance of biodegradable films intended for antimicrobial food packaging.

Antimicrobial films were prepared by including enterocins to alginate, polyvinyl alcohol (PVOH), and zein films. The physical performance of the films was assessed by measuring color, microstructure (SEM), water vapor permeability (WVP), and tensile properties. All studied biopolymers showed poor WVP and limited tensile properties. PVOH showed the best performance exhibiting the lowest WVP values, higher tensile properties, and flexibility among studied biopolymers. SEM of antimicrobial films showed increased presence of voids and pores as a consequence of enterocin addition. However, changes in microstructure did not disturb WVP of films. Moreover, enterocin-containing films showed slight improvement compared to control films. Addition of enterocins to PVOH films had a plasticizing effect, by reducing its tensile strength and increasing the strain at break. The presence of enterocins had an important effect on tensile properties of zein films by significantly reducing its brittleness. Addition of enterocins, thus, proved not to disturb the physical performance of studied biopolymers. Development of new antimicrobial biodegradable packaging materials may contribute to improving food safety while reducing environmental impact derived from packaging waste. Practical Application: Development of new antimicrobial biodegradable packaging materials may contribute to improving food safety while reducing environmental impact derived from packaging waste.