Antibiotic resistance and susceptibility to some food preservative measures of spoilage and pathogenic micro-organisms from spices

Antibiogram of 84 strains of Bacillus cereus, 26 strains of Clostridium perfringens, four strains of Staphylococcus aureus, 51 strains of Enterobacteriaceae, two strains of each of Salmonella and Shigella; isolated from spices, were studied against 20 different antibiotics that are commonly used against foodborne diseases, mainly gastroenteritis. All the tested strains of B. cereus, Cl. perfringens, Staph. aureus, Escherichia coli, Salmonella and Shigella were found resistant to at least 3, 4, 7, 6, 10 and 9 antibiotics, respectively. In brain–heart infusion broth supplemented with glucose, the D_100°C-values for B. cereus were 3.5–5.9 min, and the z-values were 17–18°C. The D_100°C-values for Cl. perfringens in fluid thioglycolate medium were higher (10.0–19.8 min) than those of B. cereus. The minimum inhibitory concentrations (MICs) of sodium chloride were 45–80 mg ml⁻¹. While the MIC of benzoic acid for Cl. perfringens, tested on perfringens agar (pH 7.3) plates by incubating anaerobially at 35°C for 24 h, was 1.9–2.2 mg ml⁻¹, for others, tested on nutrient agar (pH 6.8) plates by incubating at 35°C for 18 h in static aerobic condition, it was much less. Similarly, the MIC of sorbic acid for all the tested isolates, excepting Cl. perfringens, was 0.6–1.1 mg ml⁻¹. Of the eight isolates of Cl. perfringens, only three were inhibited at 2.0 mg sorbic acid ml⁻¹, while others were resistant. Sixty percent and 75% of the respective strains of B. cereus and Cl. perfringens were resistant to 5000 IU Nisaplin ml⁻¹, whereas the MIC values of Staph. aureus were between 3000 and 5000 IU ml⁻¹. While studying combined effect of selected hurdles on the growth of enterotoxigenic Cl. perfringens 16-C2, the judicious combination considered was low acid (pH 6.0), 30 mg sodium chloride ml⁻¹ and 1.25 mg benzoic acid ml⁻¹.     

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

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

Inactivation of Salmonella Typhimurium and Staphylococcus aureus by pulsed electric fields in liquid whole egg

In this study, the lethal effectiveness of pulsed electric fields (PEF) on the inactivation of Salmonella enterica subs. enterica ser. Typhimurium and Staphylococcus aureus in liquid whole egg (LWE) has been investigated. Maximum inactivation levels of 4 and 3 Log₁₀ cycles of the population of Salmonella Typhimurium and S. aureus were achieved with treatments of 45 kV/cm, 30 μs and 419 kJ/kg, and 40 kV/cm for 15 μs and 166 kJ/kg, respectively. The non-linear kinetics of inactivation observed for both microorganisms at all the investigated electric field strengths were described by mathematical equations based on the Weibull distribution. The developed equations enabled to compare the microbial resistance to PEF and to establish the most suitable treatment conditions to achieve a determined level of microbial inactivation. PEF treatments varying from 30 kV/cm, 67 µs and 393 kJ/kg to 45 kV/cm, 19 µs and 285 kJ/kg allow to reduce 3 Log₁₀ cycles the population of the microorganism of concern in PEF food processing of LWE, Salmonella Typhimurium.Industrial relevanceThe data presented in this investigation in terms of electric field strength, specific energy and treatment time result of relevance to evaluate the possibilities of PEF technology to pasteurize LWE with this technology. The models developed in this study can be applied to engineering design, and for the evaluation and optimization of the PEF technology as a new technique to obtain Salmonella free LWE.Based on our results it is not recommended to apply treatments of energy levels higher than 250 kJ/kg, since PEF lethality hardly increased but markedly augmented the energetic costs. For these energy values, PEF technology by itself is not sufficient (3 Log10 cycles in the best case scenario) to assure the safe security of LWE. Therefore, intelligent combinations of PEF with other preservation technologies have to be developed in order to use pulsed electric fields as an alternative to heat pasteurization of LWE.     

Effect of temperature,pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

The aim of this investigation is to evaluate the concurrent influence of temperature (4–50 °C), pH (3.5–7.0), and the presence of nisin (up to 200 μg/mL) on the inactivation of two PEF-resistant Gram-negative, pathogenic bacteria, Salmonella Typhimurium STCC 878 and Escherichia coli O157:H7, using a PEF treatment of 30 kV/cm and 99 μs. A response surface model using a central composite design was developed for the purpose of understanding the individual effects and interactions of these factors.The models showed that temperature was the factor with the greatest influence on the PEF inactivation in the two strains investigated. Increasing the treatment temperature from 4 to 50 °C increased the lethality of PEF up to at least 4 Log₁₀ reductions for both microorganisms at all pH levels investigated. PEF lethality varied with the square of the pH observing the highest microbial PEF sensitivity at pH 5.25 at all temperatures. The addition of nisin to the treatment medium did not influence the PEF lethality independently of the temperature.PEF induced 1.0–1.5 Log₁₀ cycles of damaged cells at pH 3.5 for Salmonella Typhimurium STCC 878 and at pH 5.25 for E. coli O157:H7, independently of the temperature or the presence of nisin in the treatment medium.The application of PEF at 50 °C permitted the achievement of 5 Log₁₀ reductions of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a range of pH from 4.2 to 6.7 and from 4.5 to 6.0, respectively. Therefore, the application of PEF at moderate temperatures has great potential for achieving effective control of Gram-negative pathogenic microorganisms in the range of pH found in most foods.     

Gamma irradiation as a practical alternative to preserve the chemical and bioactive wholesomeness of widely used aromatic plants

Aromatic plants require effective conservation technologies to expand their use. Irradiation might ensure plant decontamination, while maintaining their chemical, organoleptic, nutritional and bioactive qualities. In this study, the effects of gamma irradiation (1 and 10 kGy) in chemical, nutritional and antioxidant properties of Aloysia citrodora, Melissa officinalis, Melittis melissophyllum and Mentha piperita were evaluated. Gamma irradiation (up to 10 kGy) caused some statistically significant changes. However, when analyzed under an integrated approach, unirradiated and irradiated samples were grouped indiscriminately, indicating that irradiation treatment did not cause sufficient changes to define a specific chemical profile. Interestingly, each species was differentially affected by irradiation treatment. Overall, it might be considered that gamma irradiation (up to 10 kGy) is a feasible conservation technology for the assayed Lamiaceae and Verbenaceae species. This is an interesting result because the 10 kGy dose guarantees disinfested and decontaminated samples.     

A risk characterization model of Salmonella Typhimurium in Irish fresh pork sausages

A second-order simulation model was built to estimate the risk of Salmonella Typhimurium associated with the consumption of Irish fresh pork sausages. To select appropriate hazard characterization models, an initial appraisal of the current dose-response models was conducted. The cooking modality of grilling was associated with a higher mean risk of infection per serving (1.399 × 10^? 6; 95% CI: 7.54 × 10^? 7–2.65 × 10^? 6) than frying (6.246 × 10^? 7, 95% CI: 2.78 × 10^? 7–1.17 × 10^? 6). When the risk was extrapolated over the consumption in a year period, the mean risk of infection increased considerably to 8.541 × 10^? 5 with an expected number of infections and illnesses of 184.3 (95% CI: 26–664) and 17 (95% CI: 2–63), respectively. Results highlighted the importance of consumer education, as scenario analysis predicted that, for the current level of Salmonella in pork sausage, decreasing the product's cold storage by approximately 8 h and cooking for an additional half minute can reduce the current risk level by ～ 50%.     

Post-harvest treatment of cherry tomatoes by gamma radiation: Microbial and physicochemical parameters evaluation

The aim of this study was to evaluate the effects of gamma radiation on cherry tomatoes, to assess the potential of irradiation post-harvest treatment for fruit shelf-life extension. Freshly packed cherry tomatoes (Solanum lycopersicus var. cerasiforme) were irradiated at several gamma radiation doses (0.8 kGy up to 5.7 kGy) in a ⁶⁰Co chamber. Microbiological parameters, antioxidant activity and quality properties such as texture, color, pH, total soluble solids content, titratable acidity, and sensory parameters, were assessed before and after irradiation and during storage time up to 14 days at 4 °C. Inactivation studies of natural cherry tomatoes microbiota and inoculated potential foodborne pathogens (Salmonella enterica; Escherichia coli and Staphylococcus aureus) were performed. A two log reduction on the microbial load of cherry tomatoes was verified after irradiation at 3.2 kGy, and 14 days of storage at 4 °C. Moreover, a maximum reduction of 11 log on the viability of potential foodborne bacteria was obtained after irradiation at 3.2 kGy on spiked fruits. Regarding fruits quality properties, irradiation caused a decrease in firmness compared with non-irradiated fruit, although it was verified a similar acceptability among fruits non-irradiated and irradiated at 3.2 kGy. Therefore, these results suggest that the irradiation treatment could be advantageous in improving microbial safety of cherry tomatoes and shelf-life extension without affecting significantly its quality attributes.Industrial relevanceThere is an ever-increasing global demand from consumers for high-quality foods with major emphasis placed on quality and safety attributes. One of the main demands that consumers display is for minimally processed, high-nutrition/low-energy natural foods with no or minimal chemical preservatives. Extending the shelf-life, while improving the food safety, will have a positive impact on both the industry and consumers (and potential target groups such as immunocompromised patients). The present study indicated that post-harvest gamma radiation treatment of cherry tomatoes can be used as an emergent, clean and environmental friendly process to extend the shelf-life of this fruit with safety and quality.     

Application of bacteriophages during depuration reduces the load of Salmonella Typhimurium in cockles

As bivalve molluscs are filter feeder, often consumed raw or lightly cooked and are frequently cultivated in contaminated waters, they are implicated in food-borne disease transmission to human. The present study investigated the potential application of bacteriophage (or phage) phSE-2, phage phSE-5 and phage cocktail phSE-2/phSE-5 to decrease the concentration of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) during the depuration of natural and artificially contaminated cockles (Cerastoderma edule). Cockles were artificially infected with 10⁵ and 10⁶ colony-forming units (CFU)/mL of S. Typhimurium in static seawater and infected group were treated with phages at four different MOI values: 0.1, 1, 10 and 100. Depuration in static seawater at multiplicity of infection (MOI) of 0.1 with single phage suspensions of phSE-2 and phSE-5 provided the best results, as it decreased by ~ 1.3 and 1.7 log CFU/g, respectively, the concentration of Salmonella spp. after a 4 h treatment. At a MOI of 0.1, the rate of inactivation with single phage suspensions was higher when compared with the results obtained using the phage cocktail. However, in naturally contaminated cockles treated in static seawater with single phage suspensions and phage cocktail phSE-2/phSE-5, similar decreases in cultivable bacteria concentration (~ 0.7–0.9 log CFU/g) were achieved after 6 h of treatment. When artificially contaminated cockles were depurated with phage phSE-5 in a recirculated seawater system (mimicking industrial depuration conditions), a 0.9 and 2.0 log CFU/g reduction of Salmonella spp. was reached after 4 and 6 h treatment. Once the depuration process was performed without phage, a 6 h treatment was needed to obtain a 1.1 log CFU/g reduction of Salmonella spp. Results indicated that combining phage biocontrol with depuration procedures enhance bivalve microbial safety for human consumption by improving decontamination efficiency, proving that this technology can be transposed to the bivalves industry. Moreover, this approach also displays the advantage of reducing the time required for depuration and consequently its associated costs.     

Influence of γ-irradiation on the reactive-oxygen metabolism of blueberry fruit during cold storage

To explore a safe, environmentally friendly, and efficient preservation technology for blueberry (Semen trigonellae), “Bluecrop” blueberry fruits were treated with different irradiation doses. During cold storage at 0 ± 5 °C, the decay rate, fruit firmness, and indices relating to respiration and reactive-oxygen metabolism were detected regularly. Results showed that irradiation treatment with 1.0 kGy to 2.5 kGy doses was able to inhibit the respiration intensity, ethylene production, and the improvement of lipoxygenase (LOX) activity, thus reducing the increase of malondialdehyde (MDA) content and the permeability of cell membranes. In addition, irradiation treatment can improve the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) to eliminate, on a continual basis, the constantly generated superoxide anions (O₂⁻) and hydrogen peroxide (H₂O₂), keeping them at a low level: ultimately, this effectively guaranteed the storage quality and postponed the senescence process in the blueberry fruits. Meanwhile, those irradiated at 2.5 kGy presented optimal preservation effects as the respiration was inhibited to the utmost extent and the anti-oxidisation effect was enhanced. The results prove that the ⁶⁰Co γ-irradiation treatment at proper doses is an effective method of storing post-harvest blueberry fruits at low temperatures.     

Examination of the internalization of Salmonella serovar Typhimurium in peanut,Arachis hypogaea,using immunocytochemical techniques

A variety of products of plant origin, such as tomatoes, melons, peppers, and peanuts, have been implicated in Salmonella spp. associated outbreaks in recent years. Although these bacteria have been found to internalize within some plants associated with foodborne-related outbreaks, the internalization in peanut plants has not been examined to date. To investigate internalization and where the bacteria localize within the plant, intact peanut seeds were contaminated with Salmonella serovar Typhimurium expressing green fluorescent protein (GFP) for 30 min and immunocytochemical techniques were used to localize the bacterium within the stem tissue of 16 day-old peanut plants. An average of 13.6 bacteria/mm³ were localized within the sampled tissue. The bacteria were found to be associated with every major tissue (cortical, vascular, epidermal, and pith) and corresponding cell type. The cortical cells located to the outside of the vascular bundles contained the majority of the Salmonella cells (72.4%). Additional growth experiments demonstrated peanut seedlings could support the reproduction of Salmonella to high levels (10⁹ CFU/plant) after 2 days following seed contamination. Together these results show that Salmonella Typhimurium can internalize within many different plant tissue types after a brief seed contamination event and that the bacteria are able to grow and persist within the plant.     

Combined effect of γ-irradiation and osmotic pretreatment on mass transfer during dehydration

The combined effect of γ-irradiation (3.0–9.0 kGy) and osmotic pretreatment (10 and 50°B) on dehydration kinetics was studied. The exposure to irradiation pretreatment resulted in an increase in cell wall permeabilization, leading to softening of tissue, which in turn resulted in faster dehydration. The effective diffusion coefficient of water in case of potato during dehydration, considering Fickian diffusion, increased from 2.38 × 10⁻⁹ to 4.14 × 10⁻⁹ m²/s at 9.0 kGy, whereas the osmotic pretreatment resulted in lower dehydration rates due to infusion of solute from osmotic solution, which resulted in lower mass transfer rates. Even though the effective diffusion coefficients decreased from 2.38 × 10⁻⁹ to 1.55 × 10⁻⁹ m²/s (up to 50°B), the osmotic pretreatment improves nutritional, sensorial and functional properties of food without changing its integrity, apart from partial removal of water present in food. The combining of γ-irradiation treatment with osmotic pretreatment resulted in increased mass transfer rates during air dehydration, offering a feasible solution for satisfactorily enhancing the mass transfer rates.     

Distribution of ergosterol in different tissues of mushrooms and its effect on the conversion of ergosterol to vitamin D2 by UV irradiation

Analysis of ergosterol content in different tissues of Shiitake mushrooms showed a significant difference (p < 0.01) in its distribution. Thus, the conversion of ergosterol in whole mushrooms to vitamin D₂, by exposure to UV irradiation, was significantly affected (p < 0.01) by the orientation of the mushroom tissues to the UV. The highest ergosterol content was found in button mushrooms (7.80 ± 0.35 mg/g DM) while the lowest was in enoki mushrooms (0.68 ± 0.14 mg/g DM). The conversion of ergosterol to vitamin D₂ was about four times higher when gills were exposed to UV-A irradiation than when the outer caps were exposed to the same. The lowest conversion to vitamin D₂ (12.5 ± 0.28 μg/g DM) was observed for button mushrooms while the highest value (45.1 ± 3.07 μg/g DM) was observed for oyster mushrooms. The optimum moisture content of mushrooms for this conversion was around 78% on a wet basis and the temperature was around 35 °C.     

Water activity change at elevated temperatures and thermal resistance of Salmonella in all purpose wheat flour and peanut butter

Water activity (a_w) is a major factor affecting pathogen heat resistance in low-moisture foods. However, there is a lack of data for a_w at elevated temperatures that occur during actual thermal processing conditions, and its influence on thermal tolerance of pathogens. The objective of this study was to gain an in-depth understanding of the relationship between temperature-induced changes in a_w and thermal resistance of Salmonella in all purpose flour and peanut butter at elevated temperatures (80 ^oC). Equilibrium water sorption isotherms (water content vs. water activity) for all purpose wheat flour and peanut butter over the range of 20 to 80 °C were generated using a vapor sorption analyzer and a newly developed thermal cell. The thermal resistance (D₈₀-values) of Salmonella in all purpose wheat flour and peanut butter with initial a_w of 0.45 (measured at room temperature, ~ 20 °C) was determined via isothermal treatment of small (< 1 g) samples. When increasing sample temperature from 20 to 80 °C in sealed cells, the a_w of all purpose flour increased from 0.45 to 0.80, but the a_w of peanut butter decreased from 0.45 to 0.04. The corresponding estimated D₈₀-values of Salmonella in all purpose flour and peanut butter with 20 ^oC a_w of 0.45 were 6.9 ± 0.7 min and 17.0 ± 0.9 min, respectively. The significantly (P < 0.05) higher D₈₀-value of Salmonella in peanut butter than in all purpose flour may be partially attributed to the reduced a_w in peanut butter in comparison to the increased a_w in all purpose flour at 80 °C. The improved understanding of temperature-induced changes in a_w of low-moisture products of different composition provides a new insight into seemly unpredictable results, when using heat treatments to control Salmonella in such food systems.     

Raman spectroscopic study of electron-beam irradiated cold-smoked salmon

Raman spectroscopy studies have been carried out to determine the effect of electron-beam irradiation on cold-smoked salmon. Vacuum packed samples were electron-beam irradiated at doses between 0 and 8 kGy. The irradiation at 8 kGy originated modifications on the protein secondary structure with a decrease (p < 0.05) in α-helix and the concomitant increase (p < 0.05) in β-sheet, turns and unordered content. Irradiation (?1 kGy) provokes a decrease of 1518 cm^?1 band intensity of cold-smoked salmon indicating that the treatment could produce a decrease of carotenoid content.     

Biocontrol of Staphylococcus aureus in curd manufacturing processes using bacteriophages

The ability of specific bacteriophages to inhibit Staphylococcus aureus growth in curd manufacturing processes was determined. Two lytic bacteriophages specific against S. aureus were obtained by DNA random deletion from the milk-isolated temperate phages, ΦH5 and ΦA72. A cocktail of these lytic phages, Φ88 and Φ35, at multiplicity of infection (MOI) of 100, produced a complete elimination of 3×10⁶ cfu mL⁻¹ of the pathogen in ultra-high-temperature (UHT) whole milk at 37 °C. Furthermore, the frequency of emergence of bacteriophage-insensitive mutants was reduced up to 200-fold in the presence of the two lytic phages compared with that detected with the combination of the temperate counterparts. The lytic phage derivatives, added to milk, were able to decrease rapidly the viable counts of S. aureus during curd manufacture. In acid curd, the pathogen was not detected after 4 h of incubation at 25 °C, whereas pathogen clearance was achieved within 1 h of incubation at 30 °C in renneted curd. These results indicate that lytic bacteriophages could be used as biopreservatives in the manufacture of particular dairy products.     

Effect of γ-irradiation on the physicochemical and sensory properties of raw unpeeled almond kernels (Prunus dulcis)

The present study evaluated the quality of raw unpeeled almonds as a function of irradiation dose in order to determine dose levels causing minimal undesirable changes to almonds. Physicochemical (color, peroxide value, hexanal content, fatty acid composition, volatile compounds) and sensory (color, texture, odor, taste) properties of almonds were determined as a function of irradiation dose.Results showed a ten-fold increase in peroxide value (PV) after irradiation at a dose of 7 kGy. A small but statistically significant (p < 0.05) change was observed in hexanal concentration as a result of irradiation. No statistically significant (p > 0.05) changes were recorded in polyunsaturated fatty acids (PUFA) up to a dose of 7 kGy while monounsaturated fatty acids (MUFA) decreased manifested as a respective increase in saturated fatty acids (SFA) up to 3 kGy. Volatile compounds such as aldehydes, ketones and alcohols increased with increasing irradiation dose indicating enhanced lipid oxidation. Color parameter L^? decreased (p < 0.05) at doses > 3 kGy while color parameters a^? and b^? remained unaffected by irradiation. Sensory analysis showed that almonds remained organoleptically acceptable up to a dose of 3 kGy.Industrial Relevance: Irradiation is very efficient in controlling insects and growth of aflatogenic Aspergillus spp. in dry nuts.     

A systematic review and meta-analysis of the effectiveness of biosecurity and vaccination in reducing Salmonella spp. in broiler chickens

Our objective was to estimate the effectiveness of vaccination and biosecurity on the prevalence of Salmonella spp. in broiler chickens using systematic review and meta-analysis. A comprehensive search of the global primary literature was conducted in: Current Contents (1999–2009), Agricola (1924–2009), MEDLINE (1860–2009), Scopus (1960–2009), CAB (1913–2009), and Centre for Agricultural Bioscience Global Health (1971–2009). The search algorithm was (Salmonell*) AND (chicken* OR chick* OR poultry* OR broiler* OR gallus*). Additional studies were identified by contacting five topic experts and hand-scanning bibliographies of recent review articles and a recently published textbook. Studies were included if they were English language and investigated the effects of vaccination and biosecurity on the prevalence of Salmonella spp. in broiler chickens. All study design types were included. Data extraction and methodological assessment were conducted by two reviewers independently. All meta-analyses were based on random-effects models. For biosecurity, sixteen challenge studies (n = 137 treatment-control comparisons) and one controlled study (n = 2) met the inclusion criteria. Significant heterogeneity (Cochran's Q-statistic, p < 0.001) was observed among biosecurity challenge studies examining hydrogen peroxide or polyhexamethylenebiguanide hydrochloride applied to hatching eggs, making it inappropriate to present a summary effects measure. For vaccination, 19 challenge studies (n = 226) and three controlled studies (n = 10) met the inclusion criteria. Among live Salmonella Typhimurium vaccine challenge studies heterogeneity was not significant (p = 0.138). Vaccination with a live Salmonella Typhimurium reduced the risk of Salmonella cecal colonization in the treated broiler group by 35 out of 1000 broilers when compared to the control group (OR = 0.21; 95% CI = 0.06–0.77) and this effect was significant (p = 0.018). One biosecurity study (n = 2 treatment-control comparisons) and three vaccination studies (n = 10) were conducted in a commercial setting. The two included studies in the vaccination meta-analysis were both conducted at research facilities. The live Salmonella Typhimurium vaccine showed the most promise in reducing the prevalence of Salmonella in broiler ceca. However, the meta-analysis included few studies, and these studies challenged the birds with different serotypes. We recommend that more large-scale randomized, blinded trials be conducted with a live Salmonella Typhimurium vaccine on commercial farms.     

Survival of Salmonella Enteritidis PT 30 on inoculated almond kernels in hot water treatments

Almonds are blanched by exposure to hot water or steam-injected water to remove the pellicle (skin) from the kernel. This study evaluated the survival of Salmonella Enteritidis PT 30, Salmonella Senftenberg 775W and Enterococcus faecalis on whole raw almond kernels exposed to hot water. Whole, inoculated (7 to 9 log CFU/g) Nonpareil almonds (40 g) were submerged in 25 L of water maintained at 60, 70, 80 and 88 °C. Almonds were heated for up to 12 min, drained for 2 s, and transferred to 80 mL of cold (4 °C) tryptic soy broth. Almonds in broth were stomached at high speed for 2 min, serially diluted, plated onto tryptic soy and bismuth sulfite agars (Salmonella) or bile esculin agar (Enterococcus) and incubated at 37 °C for 24 and 48 h, respectively. D values of 2.6, 1.2, 0.75 and 0.39 min were calculated for exposure of S. Enteritidis PT 30 to water at 60, 70, 80 and 88 °C, respectively; the calculated z value was 35 C°. D values determined for Salmonella Senftenberg 775W and E. faecalis at 88 °C were 0.37 and 0.36 min, respectively. Neither Salmonella serovar could be recovered by enrichment of 1-g samples after almonds inoculated at 5 log CFU/g were heated at 88 °C for 2 min. These data will be useful to validate almond industry blanching processes.     

Effect of pulsed electric fields (PEF) combined with natural antimicrobial by-products against S. Typhimurium

The effect against Salmonella enterica serovar Typhimurium of PEF treatment combined with cauliflower and mandarin by-product infusions at several concentrations (0, 1, 5, and 10% (w/v)) was evaluated at various incubation temperatures (10, 22, and 37 °C). The possible synergistic antimicrobial action of the combined process of Pulsed Electric Field (PEF) technology followed by exposure to the by-product infusions and the occurrence of sublethal cellular damage were also studied. Antimicrobial kinetics of by-product infusions alone or following PEF treatment were fitted to a Weibull model. Both mandarin and cauliflower by-product infusions showed a maximum antimicrobial effect against S. Typhimurium after 10 h at 37 °C when the microorganism was exposed to 10% of by-product infusion, achieving reductions of initial bacterial load up to undetectable levels. The effect of the PEF treatment (20 kV–900 μs) caused a reduction of 4 log cycles of the initial cell population (10⁸ cfu/mL) of S. Typhimurium and 1 log cycle (90%) of cellular damage. Moreover, when the PEF pre-treated S. Typhimurium population was subjected to subsequent incubation in the presence of both by-product [10%] infusions, the microbial inactivation was faster, achieving a reduction of the initial bacterial load (4 log₁₀ cycles) up to undetectable levels in 2 h. The kinetic values of the Weibull model were obtained. The higher the concentration of by-product infusion, temperature, and PEF treatment applied, the greater the kinetic parameter “b” values, which are related to the microbial inactivation rate. Therefore, the addition of cauliflower and mandarin by-product infusions could be a good additional control measure contributing to ensure bacterial counts below recommended limits in pasteurized PEF products during their storage at refrigeration temperatures.     

Fate of enterotoxigenic Staphylococcus aureus in the presence of nisin-producing Lactococcus lactis strain during manufacture of Jben,a Moroccan traditional fresh cheese

The inhibitory effect of nisin-producing Lactococcus lactis subsp. lactis UL730 on the growth of enterotoxigenic Staphylococcus aureus J10 during manufacture of Jben, a Moroccan traditional fresh cheese prepared from recombined milk, was investigated.With an inoculum level of 10³ cfu mL⁻¹, S. aureus was absent in Jben four days after inoculation when the nisin-producing lactococcus was used as lactic starter. In contrast, it survived after that period, when the starter was non-nisin-producing. No staphylococcal thermonuclease was detected in all Jben samples made from milk inoculated with S. aureus at the level of 10³ cfu mL⁻¹.With a higher inoculum of 10⁵ cfu mL⁻¹, S. aureus was still present in Jben after manufacture and persisted during the storage of the product for 3 days in the laboratory, even when the starter used was nisin-producing. Staphylococcal thermonuclease and type C enterotoxin were detected in all Jben samples made from milk inoculated with 10⁵ cfu mL⁻¹. Thermonuclease and enterotoxin were already produced in the coagulum, at 24 h after milk inoculation with S. aureus.