Combinations of selected physical and chemical hurdles to inactivate Escherichia coli O157:H7 in apple and orange juices

This study evaluated the individual and combined efficacies of physical processing techniques such as heating, Dynashock multi-frequency ultrasound waves, ultraviolet-C (UV-C), and additives such as sodium benzoate, potassium sorbate, α- and β-Pinene for pasteurization of orange and apple juices against acid-adapted Escherichia coli O157:H7. In heated apple juice, log-linear inactivation of the test organism resulted in D values which were used to calculate for the recommended 5-log reduction process schedules (t_5D) at 45, 50, 52, 55, and 60 °C equal to 481.5, 103.6, 45.0, 22.4, and 10.54 min, respectively. E. coli O157:H7 exhibited biphasic inactivation composed of a slow inactivation lag, followed by log-linear inactivation in ultrasound-treated juice. t_5D schedules were similarly calculated at 54.7 and 77.5 min for orange and apple juice, respectively. Lethal rate analyses in the ultrasound-treated apple juice revealed that 85% of the reduction in E. coli population was due to the heat liberated by cavitation. Combined ultrasound and UV-C treatment resulted in greater inactivation rates in both juices, with greater efficacy in apple juice. Supplementation of all tested additives, whether singly or in combination, similarly resulted in significantly shorter t_5D schedules in both juices.     

High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris spores in orange juice

The spoilage of high acid fruit juices and nectars by Alicyclobacillus acidoterrestris is a major concern to juice manufacturers around the world since it is difficult to detect. In this study, thermosonication (ultrasound and heat, TS) and thermal inactivation of A. acidoterrestris spores in pretreated orange juice were carried out and resistance parameters were estimated. First, the effect of TS acoustic energy density (AED, 0.3–20.2 W/mL) on the inactivation at 75 °C was investigated. Then, the influence of TS temperature (70–78 °C) on the spore inactivation (AED = 20.2 W/mL) was studied. Next, we explored the effect of high pressure processing (HPP) pretreatment of juice on the 20.2 W/mL TS inactivation at the best temperature (78 °C). Lastly, the thermal inactivation of spores in juice heat shocked + 1 min sonicated vs. untreated juice was also investigated.Results of TS showed higher spore inactivation for higher AED (D_75°C-value of 49 min for 20.2 W/mL vs. 217 min for 0.33 W/mL). Lower D-values were obtained at higher temperatures (D_78°C-value of 28 min vs. D_70°C-value of 139 min at 20.2 W/mL). The TS D_78°C-value (at 20.2 W/mL) decreased further from 28 min to 14 min when the orange juice was previously submitted to 600 MPa for 15 min. Thermal treatment alone at 78 °C resulted in almost no spore inactivation, whereas the heat shock + ultrasound pretreatment of juice enhanced the thermal inactivation of spores (D_85°C-value decreased from 69 to 29 min). To conclude, HPP-assisted TS provided the best method for spore inactivation, indicating the benefit of high pressure and power ultrasound technology in addition to heat. TS required at least 8 °C lower temperatures than thermal treatments to achieve the same spore inactivation, which could enhance juice quality and energy savings.     

Suboptimal growth conditions induce heterologous ultraviolet-C adaptation in Salmonella enterica in orange juice

This study was conducted to determine the effects of single and simultaneous physicochemical stress exposures on the subsequent resistance of Salmonella spp. to ultraviolet-C (UV–C) in orange juice (pH 3.1, 11.5 °Brix, 0.63% citric acid). Seven strains of the test bacterium were individually subjected to suboptimal growth conditions (24 h), including gradual acidification (final pH 4.5), abrupt desiccation (a_w 0.96), heat stress by incubation at high temperature (40 °C), and combinations of acid + desiccation (pH 4.5, a_w 0.96), acid + heat (pH 4.5, 40 °C), and desiccation + heat (a_w 0.96, 40 °C). Cocktail of the different strains previously exposed to specific stress were then subjected to UV–C inactivation. The UV–C resistance of Salmonella enterica was expressed in terms of D and D_UV–C values, which correspond to the unit time of exposure and UV–C energy necessary to reduce the population by 1 log cycle (90%), respectively. Results showed that in all treatments, S. enterica exhibited logarithmic linear or first-order UV inactivation kinetics, indicating that the cells had homogenous responses towards the environmental stresses and the eventual kill step. Except for heat, all prior stress exposures resulted in cells more resistant to UV–C than the control (D = 12.7 s, D_UV–C = 63.56 mJ/cm²). Cells previously exposed to desiccation were most resistant to UV–C with a D and D_UV–C values of 16.6 s and 83.20 mJ/cm², respectively. Combining desiccation with acid (D = 16.2 s, D_UV–C = 80.88 mJ/cm²) and heat (D = 15.0 s, D_UV–C = 75.16 mJ/cm²) also resulted in relatively more resistant cells, with D and D_UV–C values greater than those exposed to acid (D = 14.9 s, D_UV–C = 74.56 mJ/cm²), acid + heat (D = 14.4 s, D_UV–C = 72.00 mJ/cm²), and heat stresses (D = 11.9 s, D_UV–C = 59.67 mJ/cm²). All (D ratio = D stress/D control >1.0) but those previously exposed to heat stress (D ratio <1.0) exhibited heterologous adaptation against UV–C in orange juice. These results provide additional evidences of the induction of heterologous UV–C tolerance response in S. enterica from environmental stresses commonly encountered by cells in food and food processing ecologies.     

Thermal death times of acid-habituated Escherichia coli and Salmonella enterica in selected fruit beverages

The study established the decimal reduction times at 60 and 73 °C (D₆₀ and D₇₃) of each of acid-adapted cocktails of Escherichia coli (NRRL 3704, ATCC 8739, ATCC 92522) and Salmonella enterica serovars Typhimurium (NRRL B-4420), Typhi (NRRL B-573), and Enteritidis (Biotech 1963) in some fruit beverages. Tested beverages included apple and orange juices, which are most commonly reported vectors of diseases; and tropical fruit beverages such as mango, guava, and soursop nectars, which are not frequently used as suspending media in thermal inactivation studies. The fruit beverages had pH of 3.30–4.73, titratable acidities of 0.15–0.64% organic acid, and soluble solids of 11.13–14.33 °Brix. At 60 °C, E. coli and Salmonella were 1.26–3.13 and 1.21–2.33 folds, respectively, more resistant to heating than at 73 °C. At 60 °C, E. coli and S. enterica had D₆₀ value ranges of 5.90 s (orange juice) to 12.42 s (guava nectar) and 7.50 s (orange juice) to 11.46 s (soursop nectar), respectively. At 73 °C, E. coli had D₇₃ values ranging from 3.56 s (apple juice) to 5.82 s (soursop nectar), while those of S. enterica ranged from 3.59 s (guava nectar) to 9.74 s (soursop nectar). The variations in the observed heat resistance in both heating temperatures were attributed to the differences in the physicochemical properties of the suspending fruit beverages. The results obtained in this work contribute to further understanding the behaviors of these pertinent pathogens in heat-treated fruit beverages. These data also provide baseline information for the establishment of heat pasteurization process schedules for better control of fruit juice product safety.     

Inactivation of Escherichia coli O157:H7 and spoilage yeasts in germicidal UV-C-irradiated and heat-treated clear apple juice

The decimal reduction times (D) of individual and composited Escherichia coli O157:H7 or spoilage yeasts in UV-C irradiated and heated (55 °C) clear apple juices (pH 3.68, 12.5 °Brix) were determined. Spoilage yeasts (D = 6.38-11.04 min) were found to be generally more UV-C resistant than E. coli O157:H7 (D = 0.5-2.76 min), while the opposite was observed in terms of thermal resistance (E. coli D=0.9-4.43 min; yeast D = 0.03-6.10 min). All spoilage yeast proliferated in the untreated juice (25 °C) while all E. coli strains were inactivated. Except for E. coli O157:H7 in UV-C irradiated apple juice, the composited inocula of both pathogenic and spoilage test organisms were less tolerant than the identified most resistant strain or species. The results of this study may be used in identifying appropriate target organisms, as well as the modes of inoculation, in challenge studies and eventually in the establishment and validation of process lethalities for apple juices and similar commodities.     

Decimal reduction times of acid-adapted and non-adapted Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes in young Cocos nucifera Linn. liquid endosperm

The study established the decimal reduction times at 55 °C (D_55 °C values) of acid-adapted and non-adapted Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in young coconut liquid endosperm. Acid adaptation of the test pathogens was conducted by cultivating cells in a gradually acidifying nutrient broth supplemented with 1% glucose. Results showed that acid adaptation had varying influence on the subsequent thermal resistances of the pathogens. The non-adapted E. coli O157:H7 exhibited the greatest resistance among the tested pathogens with a D_55 °C of 23.20 min. Prior adaptation to acidity decreased the D_55 °C to 16.16 min. On the other hand, acid adaptation increased the D_55 °C values of S. enterica and L. monocytogenes from 8.76 to 10.55 min, and from 7.47 to 18.09 min, respectively. The D_55 °C of the non-adapted E. coli O157:H7 was used to establish a pasteurization process schedule with an order of lethality equal to 5-logarithmic (99.999%) reduction. Sensory evaluation revealed that the overall acceptability, color, aroma, coconut flavor, and freshness characteristics of non-pasteurized and pasteurized liquid endosperms were not significantly different (p > 0.05). Moreover, the sensory quality attributes of coconut beverages (80:20 vol/vol endosperm-to-water ratio, soluble solids adjusted to 10 °Brix with sucrose) prepared from both non-pasteurized and pasteurized liquid endosperm samples did not significantly vary. The results obtained from the study may be used in the establishment and validation of thermal process schedules for young coconut liquid endosperm beverages.     

Inactivation of a non-pathogenic strain of E. coli by ionising radiation

Ionising radiation is an effective method to reduce pathogenic E. coli O157:H7 in meat and poultry products. Radiation sensitivity of bacteria, however, depends on several factors. After applying an irradiation dose of 1 kGy to cultures of the non-pathogenic strain of E. coli, DSM 498, grown and irradiated in nutrient broth, reductions of 3–4 decimal units were achieved (D₁₀ = 0.27 kGy). If grown on minced turkey meat, however, reduction rates were lower (D₁₀ = 0.47 kGy). Even lower reduction rates were obtained during irradiation of frozen meat (D₁₀ = 0.72 kGy) compared to treatments at cooling temperatures (D₁₀ = 0.48 kGy). For data evaluation, both, first order reduction kinetics and the Weibull model were compared. The results emphasise the necessity to determine inactivation kinetics in food matrices of target extrinsic factors (e.g. temperature).     

Evaluation of Zataria multiflora Boiss. essential oil activity against Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes by propidium monoazide quantitative PCR in vegetables

Essential oils (EOs) have long been applied as flavoring agents in foods, and due to their content in antimicrobial compounds, they have potential as natural agents for food preservation. Recently, real-time PCR in combination with PMA has successfully been applied to discriminate between live Escherichia coli O157:H7 and dead bacteria killed by cumin, clove, oregano and cinnamon EOs. In this study, initial experiments were performed in order to elucidate the minimum bactericidal concentration of Zataria multiflora EOs on E. coli O157:H7, Salmonella enterica and Listeria monocytogenes. Thereafter PMA-qPCR was applied in order to selectively quantify life cells within a bacterial population treated with Z. multiflora EO. Inactivation was obtained at EO concentrations of 0.02, 0.035, 0.045 for L. monocytogenes, E. coli O157:H7 and S. enterica, respectively. L. monocytogenes were totally killed in 30 min while it took 1 h 30 min for the gram negative pathogens. As a conclusion Z. multiflora EO has potential as natural food additive or biopreservative since it was able to irreversibly inactivate the three pathogens tested, at lower concentrations than other EOs and short exposition times. In addition, the PMA-qPCR approach proved efficient to selectively detect live pathogenic bacteria in vegetables following inactivation with Z. multiflora EO.     

Alicyclobacillus acidoterrestris spore inactivation by high pressure combined with mild heat: Modeling the effects of temperature and soluble solids

High pressure processing (HPP) comprises the application of pressures between 100 and 1000 MPa to foods for microbial inactivation and food preservation. HPP has been commercially applied to pasteurize fruit juices with the advantage of retaining its bioactive constituents and original organoleptic properties. Alicyclobacillus acidoterrestris has been suggested as a reference in the design of pasteurization for high-acid fruit products, due to spore resistance and spoilage incidents in fruit juices. In this study, A. acidoterrestris spore inactivation by 600 MPa combined with mild heat (35–65 °C) in malt extract broth adjusted to 10, 20 and 30 °Brix was carried out and the inactivation was modeled.The soluble solids increased the resistance of the spores to 600 MPa-thermal process, while the temperature decreased its resistance. Although the nonlinear Weibull model gave better fittings, the first-order kinetic parameters were also determined. For example for 600 MPa at 55 °C D_10°Brix = 4.2 min, D_20°Brix = 7.6 min, D_30°Brix = 13.7 min, and z_T-values were 20–21 °C. The z-values for the effect of soluble solids on D_T-values were 39–40 °Brix for 45 and 55 °C 600 MPa HPP. The results obtained with broth were validated with fruit juices and concentrates. The combination of HPP with heat was an effective alternative to conventional thermal processing for the inactivation of A. acidoterrestris spores in juices up to 30 °Brix, allowing the use of less 30–40 °C of temperature for the same microbial inactivation, which potentially results in more nutritious, fresher and tastier juices/concentrates.     

Inactivation of Salmonella,E. coli and Listeria monocytogenes in phosphate-buffered saline and apple juice by ultraviolet and heat treatments

Two strains of Escherichia coli (K-12 and O157:H7), Salmonella (enteritidis and typhimurium) and Listeria monocytogenes (AS-1 and M24-1) were individually suspended in phosphate-buffered saline (PBS) and apple juice prior to exposure to UV radiation (220–300 nm) and heating at 55 °C. The calculated decimal reduction times (D value, min) varied with suspending medium and mode of inactivation. The AS-1 and M24-1 strains of L. monocytogenes were found to be most resistant to UV in PBS (0.28–0.29 min) while the AS-1 strain was most resistant in juice (1.26 min). The AS-1 strain of L. monocytogenes and E. coli O157:H7 were most heat resistant when suspended in PBS (4.41 min) and juice (4.43 min), respectively. Results obtained from this study may be used by apple juice processors in selecting appropriate organisms for UV irradiation or heat treatment lethality validations.     

Inactivation of Listeria monocytogenes and Salmonella enterica serovar Senftenberg 775W inoculated into fruit juice by means of ultra high pressure homogenisation

The inactivation of Listeria monocytogenes and Salmonella enterica serovar Senftenberg 775 W by ultra high pressure homogenisation (UHPH) was evaluated in grape and orange juices inoculated at a concentration of approximately 7 log CFU/ml. The fluid inlet temperature used was 6 °C and the pressure levels assayed were 200, 300 and 400 MPa. Viable and injured bacterial counts were obtained 2 h after the UHPH treatments and after 5, 8, and 15 days of storage at 4 °C. Pressure level had a significant impact on the lethal effect of UHPH and complete inactivation of S. enterica serovar Senftenberg 775 W was achieved at 400 MPa. L. monocytogenes showed more resistance than S. enterica serovar Senftenberg 775 W to the UHPH treatments and no significant differences were observed between 300 and 400 MPa treatments in both juices. Sublethal injuries were not detected in any case. During the storage at 4 °C viable counts of both strains showed a decreasing trend. L. monocytogenes viable counts became undetectable in UHPH treated and also in control samples of grape juice which could be attributed to the presence of natural compounds with antilisterial effect.     

Inactivation of Escherichia coli O157:H7 by high pressure carbon dioxide combined with nisin in physiological saline,phosphate-buffered saline and carrot juice

The individual and combined effects of high pressure carbon dioxide (HPCD) and nisin (200 IU/mL) on the inactivation of Escherichia coli O157:H7 suspended in physiological saline (PS, pH 5.60), phosphate-buffered saline (PBS, pH 5.60 or 7.00) or carrot juice (pH 6.80) were evaluated. The pressure in this study was 5 and 8 MPa, the temperature was 25 °C–45 °C, and the treatment time was 5–65 min. Inactivation of cells in PS (pH 5.60) by HPCD followed first order kinetics, the k (the inactivation rates) increased while the D (decimal reduction time) decreased in the presence of nisin, however, the acid solution dissolving nisin rather than nisin itself played a prominent role in this combination effect with HPCD in PS buffer. The inactivation kinetics of cells in PBS (pH 5.60 or 7.00) and carrot juice (pH 6.80) by HPCD followed slow-to-fast two-stage kinetics and was fitted by the modified Gompertz equation. The M (the time at which the absolute death rate is maximum) significantly decreased in the presence of nisin. HPCD enhanced the sensitization of E. coli to nisin and the time for the complete inactivation was shortened by 2.5–5 min in PBS buffer and carrot juice by combination of HPCD and nisin (HPCD + nisin) than by HPCD alone. Regression coefficients (R²) and mean square error (MSE) were used to evaluate the model performance, indicating that the models could provide a good fitting to the experimental data.     

Reuterin,lactoperoxidase, lactoferrin and high hydrostatic pressure on the inactivation of food-borne pathogens in cooked ham

The antimicrobial effect of high hydrostatic pressure (HHP) processing combined with reuterin, lactoperoxydase system (LPS) and lactoferrin (LF) on the survival of Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Enteritidis and Escherichia coli O157:H7 in sliced cooked ham stored under strict refrigeration temperature (4 °C) and mild temperature abuse conditions (10 °C) was investigated. One day after treatment, L. monocytogenes counts in HHP at 450 MPa for 5 min were 0.8 log units lower, but a recovery was observed with counts not significantly different to those observed in control after 35 d. S. Enteritidis and E. coli O157:H7 levels were reduced around 5 log cfu/g by the pressure treatment (450 MPa/5 min) and the numbers of these pathogens did not increase significantly during the 35 d of storage at 4 °C. The individual application of reuterin and LPS influenced the survival of the three pathogens studied, extending the lag phase of L. monocytogenes and diminishing S. Enteritidis and E. coli levels throughout storage, whereas no effect was recorded when LF was added. When reuterin or LPS were applied in combination with HHP there was a synergistic antimicrobial effect against L. monocytogenes, avoiding at 4 °C the recovery observed with individual treatments. These combined treatments also kept the levels of S. Enteritidis and E. coli O157:H7 below the detection limit (<1 log unit) in cooked ham stored at 4 and 10 °C during 35 d. The results obtained in the present work suggest that HHP at 450 MPa for 5 min in combination with LPS or reuterin would be useful as a hurdle technology approach against L. monocytogenes, S. Enteritidis and E. coli O157:H7 in cooked ham.     

Reference organism selection for microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm

This study identified a reference organism for the establishment of microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm. Three different, predominant spoilage bacteria were isolated from spoiled liquid endosperm and identified through 16S rDNA sequencing, prior to propagation and eventual challenge studies. Basic Local Alignment Search Tool comparisons revealed that the isolated spoilage bacteria were Klebsiella sp., Staphylococcus sp., and Kluyvera sp (%Identity 97.34–97.82%). The isolates were propagated to mid-stationary growth phase (17 h) and thereafter suspended in liquid endosperm. The inactivation rates of the spoilage isolates in liquid endosperm subjected to plasma jet at 450 and 650 W input power settings were determined and compared to those of pathogens Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. Inactivation rates of all test organisms at 450 W (2.76–5.98 min) were significantly less (p < 0.05) than those at 650 W (1.86–3.11 min). In both power settings, S. enterica exhibited the significantly (p < 0.05) greatest resistance towards plasma treatment, while Staphylococcus sp. exhibited the least. Heat penetration studies in both power settings revealed that the temperature of the liquid endosperm did not significantly increase and did not reach bactericidal ranges (<30 °C) during plasma jet treatment, hence the observed inactivation were attributed to antimicrobial species generated by the plasma. Optical emission spectroscopy revealed that these antimicrobial species included atomic oxygen (777.41 and 844.67 nm) and ultraviolet radiation (200–280 nm). Thus, this study determined S. enterica as an appropriate target organism for the establishment of plasma jet process for coconut liquid endosperm, the inactivation rate of which shall be soon established in higher scale treatment process.     

Utility of UV-C radiation as anti-Salmonella decontamination treatment for desiccated coconut flakes

This study established the ultraviolet-C (UV-C)-mediated reduction of a cocktail of Salmonella enterica serovars, artificially inoculated onto desiccated coconut flakes. Inoculated cells exhibited biphasic inactivation behavior, characterized by an initial, log-linear population reduction, followed by a slower log-linear population decline where sublethal injury accumulated. Decimal reduction times in the faster inactivation phase (D_fast) ranged from 0.65 to 0.82 min, equivalent to UV-C energy dose of 86.58–109.22 mJ/cm². The D_slow values ranged from 21.19 to 24.21 min, equivalent to energy dose of 2822.51–3224.78 mJ/cm². A total of 3-log cycles reduction in inoculated Salmonella were observed after 40 min exposure of desiccated coconut to UV-C. Further, this 40-min process resulted in changes in the Hunter L*, a* and b* color parameter values, but were not detected by a test consumer panel as evident in the non-significant difference in the color acceptability of UV-C treated and untreated coconut flakes. The UV-C process also did not affect the general acceptability of baked coconut macaroons made from UV-C treated coconut flakes. The results obtained in this work may serve as baseline information in the development of an in- or post-process integration of a UV-C radiation step against Salmonella spp. in the desiccated coconut production process flow.     

Efficiency of high pressure treatment on inactivation of pathogenic microorganisms and enzymes in apple,orange, apricot and sour cherry juices

The purpose of this study was to investigate the effect of high hydrostatic pressure with a mild heat treatment on Staphylococcus aureus 485, Escherichia coli O157:H7 933 and Salmonella Enteritidis FDA in apple, orange, apricot and sour cherry juices. The effectiveness of the treatment on polyphenol oxidase activity in apple juice and pectinesterase activity in orange juice were also determined. An inoculum of microorganisms was completely inactivated at 350 MPa and 40 °C in 5 min. The residual polyphenol oxidase activity in apple juice after treatment at 450 MPa and 50 °C for 60 min was obtained as 9 ± 2.2%. The residual pectinesterase activity in orange juice after treatment at 450 MPa and 50 °C for 30 min was determined as approximately 7 ± 1.6%. It compares with 12 ± 0.2% at a treatment of 40 °C and 450 MPa for 60 min. Pressure resistant isoenzymes were thought to be responsible for the final residual activity. The inactivation is irreversible and the enzyme is not reactivated upon storage. High pressure processing constitutes an effective technology to inactivate the enzymes in fruit juices. Pressures higher than 400 MPa can be combined with mild heat (<50 °C) to accelerate enzyme inactivation.     

Water reconditioning by high power ultrasound combined with residual chemical sanitizers to inactivate foodborne pathogens associated with fresh-cut products

The suitability of high power ultrasound (HPU, 20 kHz, 0.28 kW/l) combined with residual chemical sanitizers for water reconditioning was studied. A synergetic disinfection effect was observed when HPU was combined with peroxyacetic acid (PAA) or a commercial mix of organic acids and phenolic compounds (OA/PC). In recycled water (RW) with a chemical oxygen demand (COD) of 500 mg O₂/l, PAA inactivated 2 log units of Escherichia coli O157:H7 at concentrations of 3.2, 6.4, 16 mg/l after 7 min, 2 min, 29 s, respectively. The OA/PC or HPU treatments alone needed 26 min treatments to achieve the same reduction. The addition of TiO₂ (5 g/l) to HPU (sonocatalysis) did not improve E. coli O157:H7 inactivation. However, when HPU was combined with a residual concentration of PAA (3.2 mg/l), the total inactivation of E. coli O157:H7 and Salmonella (6 log unit reductions) occurred after 11 min, but for Listeria monocytogenes only 1.7 log reductions were detected after 20 min. When HPU was combined with OA/PC, a synergistic effect for the inactivation of E. coli O157:H7 was also observed, but this sanitizer significantly modified the physical-chemical quality characteristics of the RW. These results show that the residual PAA concentration that can be found in the wash water combined with HPU could result in an environmentally friendlier and toxicologically safer strategy for water reconditioning of the fresh-cut industry. The use of the sanitizer alone requires higher concentrations and/or longer contacts times. Even though the residual PAA in combination with HPU was adequate for water reconditioning, it is not appropriate for the process wash water because this wash water must be instantaneously disinfected.     

Thermal inactivation of Salmonella Typhimurium on dressed chicken skin previously exposed to acidified sodium chlorite or carvacrol

Salmonella is a leading cause of foodborne illness and live poultry is a main reservoir of this pathogen, worldwide. Cross-contamination and transportation of contaminated poultry meat act as an important vehicle of Salmonella infections in humans. In this study, we assessed the effect of two antimicrobials; acidified sodium chlorite (ASC) and carvacrol followed by thermal treatment to inactivate Salmonella Typhimurium on dressed chicken skin. D-values (time in min for the pathogen to decrease by 90%) of Salmonella Typhimurium at 56, 60 and 64 °C on dressed chicken skin in the control samples, determined by linear regression, were 6.17, 3.16, 1.32 min, respectively. Two D-values calculated using a logistic model, ranged from 6.28 (D_1, major population, plus T_L) and 11.66 (D_2, heat-resistant subpopulation, plus T_L) min at 56 °C to 1.08 (D₁ plus T_L), and 2.07 (D₂ plus T_L) min at 64 °C. Pre-dipping in 100–300 ppm ASC or 0.02–0.06% carvacrol rendered the pathogen more sensitive to the lethal effect of heat. Thus, combination of antimicrobials with thermal inactivation was more effective in reducing heat resistance of the pathogen on dressed chicken surface. The model developed will assist poultry processors in estimating the time required for specific log reductions of Salmonella Typhimurium on chicken skin and thus, will contribute in designing acceptance limits at critical control points for chicken skins at lower times and temperatures for cooking.     

Determination of thermal inactivation kinetics of Listeria monocytogenes in chicken meats by isothermal and dynamic methods

The objective of this research is to determine the thermal inactivation kinetics of Listeria monocytogenes in chicken breast meat under both isothermal and dynamic conditions. A four-strain cocktail of L. monocytogenes was inoculated to chicken breast meat. Isothermal studies were performed by submerging samples under hot water maintained at constant temperatures ranging from 54 to 66 °C. The D values at each temperature were determined and used to calculate the z value, using log(D) = log(D₀) − T/z. Dynamic studies were conducted by submerging samples in a water bath with its temperature programmed to increase linearly from 30 to 65 °C at 1.25 °C/min or 1.73 °C/min. A method was developed to determine the kinetic parameters from linear heating temperature profiles.The thermal inactivation of L. monocytogenes in chicken breast meat followed the first-order kinetics. The z value determined from the isothermal studies was 4.95 °C, which is very close to the values reported in the literature. The dynamic method can also be used to determine the thermal inactivation kinetics of L. monocytogenes. The average z value (4.10 °C) determined by the dynamic method was slightly lower than that determined by the isothermal method. However, the parameters (D₀ and z) determined from both isothermal and dynamic methods can be used to estimate the survival of L. monocytogenes exposed to linear heating temperature profiles, with statistically equal accuracies.The dynamic method explored in this study can be used to determine the D₀ and z values of microorganisms that exhibit first-order kinetics and are exposed to linear heating temperature profiles. Compared to the isothermal method, the dynamic method requires few data points and is equally accurate.     

Effects of culture conditions on the subsequent heat inactivation of E. coli O157:H7 in apple juice

Escherichia coli O157:H7 cells were grown in various acidic growth media including an acidogenic nutrient broth (NB) supplemented with 1% glucose (NBG) and NB acidified to pH 4.5 with 0.25% citric or malic acids. The pH in NBG continuously decreased, reaching a final pH of 4.46 after 28 h. The pH in the control culture (NB) did not significantly change throughout the incubation. When heated in apple juice at 55 °C, cells grown in NBG had the significantly highest D₅₅ value (250 ± 39.67 s). Thermal inactivation rates established for cells grown in NB, citric acid- and malic acid-acidified NBs were 51.39 ± 1.34, 25.46 ± 1.21, and 45.42 ± 0.36 s, respectively. When compared with the D₅₅ values of cells previously exposed to combinations of environmental stress factors, cells grown in NBG were also found to be significantly heat resistant and were deemed appropriate to be used in heat challenge studies.