Foodborne pathogen inactivation in fruit juices utilizing commercial scale high-pressure processing: Effects of acidulants and pH.

The effects of juice pH, type of acidulant, and post-treatment refrigeration on the high-pressure processing (HPP) inactivation of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in acid beverages were evaluated. Inoculated apple, orange, and grape juices (at their original pH and adjusted to pH 4.00, 4.50, and 5.00) were treated at 550 MPa for 1 min at 5 °C. In addition, inoculated model solutions acidified to a pH of 5.00 with acetic, citric, malic, and tartaric acids were treated at 400 MPa for 1 min at 5 °C. The effect of refrigerated storage for 24 h after treatment on pathogen inactivation in both experiments was also assessed. A greater than 5-log reduction of the three pathogens inoculated was achieved in all juices immediately after HPP at the juices' original pH, and of L. monocytogenes under all experimental conditions. Refrigerated storage for 24 h after HPP treatment improved the inactivation of E. coli O157:H7, to >5-log reduction, at pH 4.00 in apple juice and of Salmonella in the three juices at pH 4.00. The type of acidulant did not significantly (p > 0.01) affect E. coli or Salmonella inactivation in acidified model solutions but a greater than 5-log reduction after HPP was only achieved for L. monocytogenes when acetic acid was used. The effectiveness of HPP for pathogen inactivation depended largely on product pH and the target pathogen of concern.

Análisis de posibles peligros en leche materna donada. Revisión / Analysis of potential hazards in donated breast milk. Review

La leche materna donada es un recurso de alto valor que puede ser utilizado para la alimentación de neonatos hospitalizados y a término, por tanto, garantizar su inocuidad es imperativo. Esta revisión de literatura reúne los principales peligros de naturaleza física, química y microbiológica identificados en leche materna, con la intención de proveer una referencia que los consolide de tal forma que la información pueda ser utilizada por bancos de leche humana, gobiernos y agencias regulatorias para establecer mecanismos para su prevención y control. Se realizó una revisión de literatura entre agosto del 2021 y octubre del 2022, utilizando buscadores y descriptores específicos para peligros de transmisión alimentaria en leche materna. Se incluyeron estudios publicados en español o en inglés. Se identificaron 31 agentes biológicos patógenos incluyendo bacterias, virus y parásitos. Como peligros químicos se reportaron medicamentos, drogas, cafeína, infusiones herbales, micotoxinas, alérgenos, especias, suplementos nutricionales, contaminantes ambientales y desinfectantes. Se alerta sobre la presencia potencial de plástico y vidrio de tamaño menor a 7 mm proveniente del ambiente de extracción y recipientes. La presencia de peligros microbiológicos y químicos en leche materna puede darse por transmisión vertical, temperaturas inadecuadas durante el almacenamiento y contaminación en el proceso. La presencia de peligros físicos se relaciona con la manipulación de los implementos en etapas posteriores a la extracción. Se requiere prestar atención a los hábitos de la madre para prevenir peligros químicos, así como más investigación relacionada con micotoxinas en leche materna(AU)

Donated breast milk is a highvalue resource which can be used to feed hospitalized neonates and full-term infants, therefore, ensuring its safety is imperative. This literature review presents the main hazards of physical, chemical and microbiological nature identified in human milk, with the intention of providing a reference that consolidates the reported hazards reported, so the information can be used by human milk banks, governments and regulatory agencies to establish prevention and control mechanisms. A literature review was carried out between August 2021 and October 2022, using search engines and specific descriptors for foodborne hazards in breast milk. Studies published in Spanish and English were considered. 31 pathogenic biological agents including bacteria, viruses and parasites were identified. Medications, drugs, caffeine, herbal infusions, mycotoxins, allergens, spices, nutritional supplements, contaminants of environmental origin and disinfectants were reported as chemical hazards. No physical hazards were identified, however the potential presence of plastic and glass smaller than 7 mm from the extraction environment or containers is alerted. Presence of microbiological and chemical hazards can be due to vertical transmission, inadequate temperature of storing, contamination during extraction, packaging, and infant feeding. Whereas presence of physical hazards is related to implements handling after extraction. Attention to hygiene and habits of the mother to prevent chemical hazards and further research related to mycotoxins in human milk is required(AU)

Fruit-Based Fermented Beverages: Contamination Sources and Emerging Technologies Applied to Assure Their Safety.

The food and beverage market has become broader due to globalization and consumer claims. Under the umbrella of consumer demands, legislation, nutritional status, and sustainability, the importance of food and beverage safety must be decisive. A significant sector of food production is related to ensuring fruit and vegetable conservation and utilization through fermentation. In this respect, in this review, we critically analyzed the scientific literature regarding the presence of chemical, microbiological and physical hazards in fruit-based fermented beverages. Furthermore, the potential formation of toxic compounds during processing is also discussed. In managing the risks, biological, physical, and chemical techniques can reduce or eliminate any contaminant from fruit-based fermented beverages. Some of these techniques belong to the technological flow of obtaining the beverages (i.e., mycotoxins bound by microorganisms used in fermentation) or are explicitly applied for a specific risk reduction (i.e., mycotoxin oxidation by ozone). Providing manufacturers with information on potential hazards that could jeopardize the safety of fermented fruit-based drinks and strategies to lower or eliminate these hazards is of paramount importance.

Effect of high intensity ultrasound on main bioactive compounds, antioxidant capacity and color in orange juice.

Ultrasound is a useful alternative to thermal processing that can be applied to many food products and juices to aid with enzymes and microorganism inactivation and to improve the efficiency of unit operations generally applied in the food industry. The aim of this study was to evaluate the effect of a high-intensity sonication treatment (frequency 20 kHz; intensity 39.4 W/cm2) applied for treatment times from 0 to 105 min on the content of polyphenols, vitamin C, organic acids, and carotenoids, and on the hydrophilic and lipophilic antioxidant capacity and color of orange juice. Treatments were performed in triplicate and data was statistically analyzed. Sonication time did not have a significant effect (P > 0.05) on total polyphenols, total vitamin C, organic acid, and carotenoid contents, lipophilic antioxidant capacity, or juice color. The hydrophilic antioxidant activity and the lutein content increased significantly (P < 0.05) with increased sonication time. These results may be useful as a baseline for the development of sonication treatments that could be used in combination with other traditional and emerging processing approaches to protect the most important bioactive compounds and quality properties of orange juice.

First characterization of the probiotic potential of lactic acid bacteria isolated from Costa Rican pineapple silages.

BACKGROUND: Agro-industrial waste from tropical environments could be an important source of lactic acid bacteria (LAB) with probiotic potential. METHODS: Twelve LAB isolates were isolated from pineapple silages. The species identification was carried out considering 16S rRNA and pheS genes. Experiments to evaluate the probiotic potential of the isolates included survival under simulated gastrointestinal environment, in vitro antagonistic activity (against Salmonella spp. and Listeria monocytogenes), auto-aggregation assays, antibiotic susceptibility, presence of plasmids, adhesiveness to epithelial cells, and antagonistic activity against Salmonella in HeLa cells. RESULTS: Lacticaseibacillus paracasei, Lentilactobacillus parafarraginis, Limosilactobacillus fermentum, and Weissella ghanensis were identified. Survival of one of the isolates was 90% or higher after exposure to acidic conditions (pH: 2), six isolates showed at least 61% survival after exposure to bile salts. The three most promising isolates, based on survivability tests, showed a strong antagonistic effect against Salmonella. However, only L. paracasei_6714 showed a strong Listeria inhibition pattern; this isolate showed a good auto-aggregation ability, was resistant to some of the tested antibiotics but was not found to harbor plasmids; it also showed a high capacity for adhesion to epithelial cells and prevented the invasion of Salmonella in HeLa cells. After further in vivo evaluations, L. paracasei_6714 may be considered a probiotic candidate for food industry applications and may have promising performance in acidic products due to its origin.

Evaluation of high pressure processing (HPP) inactivation of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in acid and acidified juices and beverages.

Increasing consumer demand for high-quality foods has driven adoption by the food industry of non-thermal technologies such as high pressure processing (HPP). The technology is employed as a post-packaging treatment step for inactivation of vegetative microorganisms. In order to evaluate HPP inactivation of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in acid and acidified juices and beverages, pressure tolerance parameters were determined using log-linear and Weibull models in pH-adjusted apple juice (pH 4.5) at 5 °C. A commercial processing HPP unit was used. The Weibull model better described the inactivation kinetics of the three tested pathogens. According to estimates from the Weibull model, 1.5, 0.9, and 1.5 min are required at 600 MPa to produce 5-log reductions of E. coli, Salmonella, and L. monocytogenes, respectively, whereas according to the log-linear model, 3.2, 1.8, and 2.1 min are required. The effects of process conditions were verified using commercial products (pH between 3.02 and 4.21). In all tested commercial juices or beverages, greater than 5-log reductions were achieved for all tested pathogens using HPP process conditions of 550 MPa for 1 min. These findings demonstrate that the HPP conditions of 600 MPa for 3 min, typically used by the food industry provide an adequate safety margin for control of relevant vegetative pathogens in acid and acidified juices and beverages (pH < 4.5). Results from this study can be used by food processors to support validation studies and may be useful for the future establishment of safe harbors for the HPP industry.

Reducción de sodio en salsa de tomate y mayonesa mediante la aplicación de un enfoque de umbral sensorial / Sodium reduction in tomato sauce and mayonnaise through the application of a sensory threshold approach

El consumo excesivo de sodio es causa importante de enfermedades no transmisibles incluyendo hipertensión. En esta investigación se evaluó una metodología sensorial para reducir el contenido de sodio en salsas de tomate y mayonesas, productos altamente consumidos en Costa Rica. Se caracterizaron, por triplicado, 16 salsas y 7 mayonesas comerciales para determinar los ingredientes más comunes y sus características físicoquímicas. Se comparó el contenido de sodio reportado en la etiqueta contra el valor determinado experimentalmente. Se formularon prototipos de ambos productos y se determinó el umbral de diferencia apenas perceptible (DAP) para el gusto salado utilizando el método de estímulo constante con 40 panelistas no entrenados (d'= 1, significancia de 0,05 y potencia de prueba de 0,95). Se contruyeron las curvas psicofísicas con concentraciones de sal entre 0,67% y 2,5% para salsa de tomate y 0,13% y 4,16% para mayonesa; obteniéndose DAPs de 0,51% y 0,26% respectivamente; equivalentes a 28,3% y 14,4% menos de sal en cada producto. Para la validación del umbral, se aplicó una prueba de discriminación 2-AFC con 40 panelistas comparando la formulación regular con la reducida en sodio. Los panelistas no detectaron diferencias significativas entre mayonesas (P>0,05) pero sí entre salsas (P<0,05), por lo que se aplicó una prueba de agrado con 112 consumidores y se determinó que la salsa reducida en sodio resultó de mayor o igual agrado que la contraparte. Estos resultados guiarían a la industria alimentaria regional hacia el mejoramiento del perfil nutricional de estos productos(AU)

The excessive consumption of sodium is an important cause of noncommunicable diseases including hypertension. This research aimed, using a sensorial methodology, to reduce sodium content in tomato sauces and mayonnaise, highly consumed products in Costa Rica. A total of 16 commercial sauces and 7 mayonnaises were characterized to determine their most common ingredients and physicochemical properties. The sodium content reported in the labed was compared against values obtained experimentally. Prototypes for both products were developed and the threshold for the just noticiable difference (JND) for salty flavor was determined using the constant stimulus method with 40 panelists (d'= 1, 0.05 significance and a test power of 0,95). Psychophysical curves were built with salt concentrations between 0.67% and 2.5% for tomato sauce and 0.13% and 4.16% for mayonnaise; obtaining JNDs of 0.51% and 0.26% respectively; equivalent to 28.3% and 14.4% less salt in tomato and mayonnaise. To validate the threshold, a discriminatory 2-AFC test with 40 panelists was performed to compare the regular formulations against those reduced in sodium. Panelists did not detect significant differences among mayonnaises (P>0.05) but they did found differences between sauces (P<0.05). Thus, for tomato sauce a consumer liking test with 112 consumers was performed and it was found that sodium reduced tomato sauce was equally or more liked than its counterpart. These results guide the regional food industry towards the improval of the nutritional profile of both products(AU)

Fate of Spoilage and Pathogenic Microorganisms in Acidified Cold-Filled Hot Pepper Sauces.

Consumption of spicy foods and hot sauces is currently a popular trend worldwide. Shelf-stable acidified sauces are commonly hot-filled to ensure commercial sterility, but cold-fill-hold processes might also be suitable if microbial safety and stability are ensured. For this study, model acidified hot pepper sauces were developed and characterized. The effects of sauce pH and of two different organic acids on the survival of Pichia manshurica and Lactobacillus curvatus isolated from contaminated commercial hot sauces and on pathogenic Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes were assessed. Full factorial designs with three levels for pH (3.2, 3.5, and 3.9) and two for organic acid (citric and acetic) were used to determine the effects of these factors and their interactions on the survival of the microorganisms. Commercially sterile sauces were independently inoculated and kept at ambient temperature. Microbial counts were determined at different sampling times, depending on the treatment evaluated. Sauces acidified to pH 3.2 with citric or acetic acid were inoculated with cocktails of five strains or serotypes of the three pertinent pathogens, and inactivation curves were determined. Trials were performed in triplicate. A greater than 5-log reduction of P. manshurica and L. curvatus was achieved in less than 6 h in sauces adjusted to pH 3.2 with acetic acid. Greater than 5-log reductions of pathogenic bacteria were achieved 0.5 h after inoculation in sauces acidified to pH 3.2 with acetic acid. In contrast, at least 48 h was required to guarantee the same inactivation for the most tolerant pathogen when citric acid was used. Thus, a cold-fill-hold process may be a suitable alternative for acidified hot pepper sauces. Based on survival of the microorganisms evaluated in this study, microbial safety and stability can be achieved by adjusting the pH to 3.2 or less by the addition of acetic acid.

Detección de gluten en alimentos etiquetados como libres de gluten disponibles en el mercado costarricense / Gluten detection in foods labeled as gluten-free available in the Costa Rican marke

La presencia de gluten en alimentos etiquetados como libres de gluten (LG) representa una preocupación para la salud de pacientes celíacos, y personas intolerantes y sensibles a este conjunto de proteínas. Sin embargo, esto no ha sido estudiado aún en países centroamericanos. Por tanto, se investigó la presencia de gluten en alimentos etiquetados LG, manufacturados en Costa Rica y disponibles en el mercado entre los años 2016 y 2017 para determinar así el cumplimiento de las regulaciones nacionales e internacionales. Se ha estipulado que dichos alimentos deben contener <20 ppm de gluten. Un total de 173 productos fueron analizados por inmunoensayo (tres muestras por producto; cada una de un lote diferente) utilizando el kit ELISA RIDASCREEN®. 60 marcas de productos, de 32 compañías diferentes, fueron evaluadas identificando 15 categorías de alimentos LG: productos horneados, premezclas y harinas, snacks, granos y cereales, salsas, productos cárnicos, productos de origen marino, bebidas, productos lácteos, pastas, chocolates, aceites, tortillas y arepas, jaleas y mermeladas y otros. Una muestra de uno de los productos analizados presentó >20 ppm de gluten. No obstante, al menos una muestra de 49 productos diferentes (28% de los productos analizados) presentó una concentración cuantificable de gluten (>5 ppm) evidenciando una alta variabilidad en los resultados. Esta investigación evidencia el fuerte compromiso de la industria alimentaria costarricense para cumplir la norma que regula la producción de alimentos LG durante el período de estudio, aunque se alerta acerca de la necesidad de implementar mejoras en los sistemas de producción y vigilancia de estos alimentos(AU)

The presence of gluten in gluten free (GF) labelled foods represents a serious health concern to celiac patients and persons intolerant or sensitive to this set of proteins. However, this has not yet been studied in Central American countries. Therefore, the presence of gluten in foods labeled LG, manufactured in Costa Rica and available in the market, between 2016 and 2017, was investigated to determine compliance with national and international regulations. It has been stipulated that such foods must contain <20 ppm of gluten. A total of 173 products were analyzed by immunoassay (three samples per product; each from an independent batch), using the ELISA RIDASCREEN® kit. 60 product brands, from 32 different companies, were evaluated and 15 GF food categories were identified: baked products, baking mixes and flours, snacks, grains and cereals, sauces, meat products, seafood, beverages, dairy products, pasta, chocolates, oils, tortillas and arepas, jams and jellies, and others. Only one sample from one of the tested products presented >20 ppm of gluten. However, at least one sample of 49 different products (28% of products tested) presented a quantifiable concentration of gluten (>5 ppm), showing a high variability of results. This research evidences the strong commitment of the Costa Rican food industry to comply with the norm that regulates the production of LG foods during the study period, even though it warns about the need to implement improvements in the production and surveillance systems of these foods(AU)

Microbial Safety and Quality Evaluation of UV-Treated, Cold-Pressed Colored and Turbid Juices and Beverages.

The growing demand for fruit and vegetable juice blends, with improved nutritional and sensory attributes, has prompted the industrial adoption of nonthermal processing technologies, including UV light. Limited studies have explored conditions to overcome the well-known limitations of UV when treating liquid foods with a high content of particles that absorb or scatter UV light. This study addressed the effectiveness of the application of UV light, using a commercial processing unit, to inactivate pathogenic Escherichia coli O157:H7, Salmonella enterica (hereafter Salmonella), and Listeria monocytogenes, as well as spoilage microorganisms, in colored and turbid juices and beverages. The inactivation of cocktails of five strains (or serotypes) of E. coli O157:H7, Salmonella, and L. monocytogenes isolated from fruit- and vegetable-derived products linked to outbreaks was determined in seven colored and turbid cold-pressed juices and beverages. Juices and beverages were UV treated at a constant flow rate of 150 L/h through multiple consecutive passes. The inactivation of aerobic mesophilic bacteria, molds and yeasts, and lactic acid bacteria was also assessed at the cumulative dose that guaranteed a 5-log reduction of the most UV-tolerant pathogen for each product. A 5-log reduction of the three pathogens was achieved in all juices and beverages at a maximum cumulative UV dose of 12.0 ± 0.6 mJ/cm2. The dose required to ensure the targeted reduction varied depending on the tested product and the inoculated pathogen. The reduction of aerobic mesophiles, molds and yeasts, and lactic acid bacteria varied from 0.5 to 3.6, from 0.2 to 2.0, and from 0.5 to 3.6 log CFU/mL, respectively. Thus, the proposed treatment represents a suitable processing alternative to ensure the safety and extend the shelf life of colored and turbid cold-pressed juices and beverages.

Effect of Water Activity on the Thermal Tolerance and Survival of Salmonella enterica Serovars Tennessee and Senftenberg in Goat's Milk Caramel.

The low thermal tolerance of Salmonella enterica in foods with intermediate moisture levels, such as caramel sauces, ensures that mild heat treatment is sufficient to achieve 5-log reductions of this pathogen. This treatment mitigates the risk posed by salmonellae in raw materials; however, recontamination might occur because of survival of the pathogen in products that are not heated before consumption. This study was conducted to evaluate the effect of water activity (aw) on the thermal tolerance and survival of S. enterica serovars Tennessee and Senftenberg. The D-values at 76, 78, and 80°C, z-values, and survival at 20.0 ± 0.5°C for 32 weeks of these two serovars were determined in goat's milk caramel at three aw values (0.85, 0.90, and 0.93). The highest thermal tolerance was observed at aw = 0.85 for Salmonella Senftenberg (D76°C = 2.9 ± 0.3 min), and the lowest was at aw = 0.93 for Salmonella Tennessee (D80°C = 0.131 ± 0.007 min). After a logarithmic transformation of the z-values, a significant interaction between serovar and aw was found (P < 0.0001), but no consistent trends were observed at the three evaluated aw levels for either serovar. Survival response was modeled using two sigmoidal three-parameter models. A significant interaction was found between nominal variables aw and serovar when comparing inflection points of the resulting curves: P < 0.0016 for the logistic model (R2 = 0.91) and P < 0.0014 for the Gompertz model (R2 = 0.92). Although a >8-log reduction was observed at week 20 of storage, regardless of the product's aw and the serovar, low levels of salmonellae were found in the product up to week 32 of storage. Our findings may assist the food industry with the establishment of critical limits for the safe thermal treatment of milk- and sugar-based foods with intermediate moisture levels. The survival data presented here highlight the relevance of implementing and effectively maintaining good sanitation and hygiene practices during the production of goat's milk caramel and similar food products.

UV Tolerance of Spoilage Microorganisms and Acid-Shocked and Acid-Adapted Escherichia coli in Apple Juice Treated with a Commercial UV Juice-Processing Unit.

The enhanced thermal tolerance and survival responses of Escherichia coli O157:H7 in acid and acidified foods is a major safety concern for the production of low-pH products, including beverages. Little is known about this phenomenon when using UV light treatments. This study was conducted to evaluate the effects of strain (E. coli O157:H7 strains C7927, ATCC 35150, ATCC 43895, and ATCC 43889 and E. coli ATCC 25922) and physiological state (control-unadapted, acid adapted, and acid shocked) on the UV tolerance of E. coli in apple juice treated under conditions stipulated in current U.S. Food and Drug Administration regulations. A greater than 5-log reduction of E. coli was obtained under all tested conditions. A significant effect of strain (P < 0.05) was observed, but the physiological state did not influence pathogen inactivation (P ≥ 0.05). The UV sensitivity of three spoilage microorganisms (Aspergillus niger, Penicillium commune, and Alicyclobacillus acidoterrestris) was also determined at UV doses of 0 to 98 mJ/cm(2). Alicyclobacillus was the most UV sensitive, followed by Penicillium and Aspergillus. Because of the nonsignificant differences in UV sensitivity of E. coli in different physiological states, the use of an unadapted inoculum would be adequate to conduct challenge studies with the commercial UV unit used in this study at a UV dose of 14 mJ/cm(2). The high UV tolerance of spoilage microorganisms supports the need to use a hurdle approach (e.g., coupling of refrigeration, preservatives, and/or other technologies) to extend the shelf life of UV-treated beverages.

Determination of the validation frequency for commercial UV juice processing units.

The CiderSure 3500 is one of the most commonly used UV juice processing units in the United States for the nonthermal processing of apple cider and fulfills the 5-log performance standard established by the federal juice HACCP regulation. However, the appropriate validation frequency of this machine's quartz tubes is currently unknown by juice processors and regulatory agencies. Presently, an annual validation is recommended by the manufacturer. Historical validation data from 1998 to 2013 of commercially used quartz tubes underwent comprehensive statistical analysis. A total of 400 tubes were validated one time, and 212 of those units were revalidated at least once over the evaluated time frame. Validations were performed at 14 mJ·cm(-2) UV dose and under turbulent flow conditions. Every validation showed a greater than 5-log reduction of Escherichia coli ATCC 25922, a nonpathogenic surrogate for pathogenic E. coli O157:H7, in each of three replicates. For initial validations, a mixed-effect model with log reduction of E. coli as response was constructed (400 tubes analyzed in triplicate). The model showed that the year of analysis and the initial inoculum level significantly affected the log reduction of E. coli (P < 0.0001), which on average was 7.0 ± 0.7. A quadratic relationship between the year of analysis and the response was found. Likewise, for revalidations (212 tubes analyzed in triplicate), the constructed random coefficient model showed that the year of analysis, quadratic effect of year of analysis, and initial inoculum level significantly affected the log reduction of E. coli (P < 0.0001). For this model, the major source of variance was explained by the year of analysis. The models describe the UV reactor's performance over time and suggest that a validation frequency of every 3 years would be conservatively adequate during the first 8 years of quartz tube use. After that, due to the reported quadratic trend, yearly validation would be recommended.

Effect of acid adaptation and acid shock on thermal tolerance and survival of Escherichia coli O157:H7 and O111 in apple juice.

Gradual exposure to moderate acidic environments may enhance the thermal tolerance and survival of Escherichia coli O157:H7 in acid and acidified foods. Limited studies comparing methodologies to induce this phenomenon have been performed. The effects of strain and physiological state on thermal tolerance and survival of E. coli in apple juice were studied. The decimal reduction time (D-value) at 56°C [D56°C] was determined for E. coli O157:H7 strains C7927 and ATCC 43895 and E. coli O111 at four physiological states: unadapted, acid-shocked (two methodologies used), and acid-adapted cells. The effect of acidulant was also evaluated by determining the D56°C for the O157:H7 strains subjected to acid shock during 18 h in Trypticase soy broth (TSB), with pH 5 adjusted with hydrochloric, lactic, and malic acids. Survival of the three strains at four physiological states was determined at 1 ± 1°C and 24 ± 2°C. Experiments were performed in triplicate. For thermal inactivation, a significant interaction was found between strain and physiological state (P < 0.0001). Highest thermal tolerance was observed for the 43895 strain subjected to acid shock during 18 h in TSB acidified with HCl (D56°C of 3.0 ± 0.1 min) and the lowest for the acid-shocked C7927 strain treated for 4 h in TSB acidified with HCl (D56°C of 0.45 ± 0.06 min). Acidulants did not alter the heat tolerance of strain C7927 (D56°C of 1.9 ± 0.1 min; P > 0.05) but significantly affected strain 43895 (P < 0.05), showing the greatest tolerance when malic acid was used (D56°C of 3.7 ± 0.3 min). A significant interaction between strain, storage temperature, and physiological state was noted during the survival experiments (P < 0.05). E. coli O111 was the most resistant strain, surviving 6 and 23 days at 24 and 1°C, respectively. Our findings may assist in designing challenge studies for juices and other pH-controlled products, where Shiga toxin-producing E. coli represents the pathogen of concern.

Thermal resistance parameters of acid-adapted and unadapted Escherichia coli O157:H7 in apple-carrot juice blends: effect of organic acids and pH.

Numerous outbreaks involving fresh juices contaminated with Escherichia coli O157:H7 have occurred in the United States and around the world, raising concern for the safety of these products. Until now, only a few studies regarding the thermal tolerance of this pathogen in acidic juices over a wide range of pH values have been published. Therefore, the effect of varying the pH with different organic acids on the thermal inactivation of non-acid-adapted and acid-adapted E. coli O157:H7 (strain C7927) was determined. The decimal reduction times (D-values) and the change in temperature required for the thermal destruction curve to traverse 1 log cycle (z-values) were calculated for non-acid-adapted E. coli in an apple-carrot juice blend (80:20) adjusted to three pH values (3.3, 3.5, and 3.7) by the addition of lactic, malic, or acetic acid and at a pH of 4.5 adjusted with NaOH. Thermal parameters were also determined for acid-adapted cells in juices acidified with malic acid. The effect of the soluble solids content on the thermal tolerance was studied in samples with a pH of 3.7 at 9.4 to 11.5 °Brix. The D-values were determined at 54, 56, and 58 °C, and trials were conducted in triplicate. Non-acid-adapted E. coli exhibited the highest thermal tolerance at pH 4.5 (D-value at 54 °C [D54 °C] of 20 ± 4 min and z-value of 6.2 °C), although on average, the D-values increased significantly (P < 0.01) due to acid adaptation. In acidified juices, the highest tolerance was observed in acid-adapted E. coli in samples adjusted to pH 3.7 with malic acid (D54 °C of 9 ± 2 min and z-value of 5.4 °C) and the lowest in unadapted E. coli at pH 3.3 acidified with acetic acid (D58 °C of 0.03 ± 0.01 min and z-value of 10.4 °C). For juices acidified to the same endpoint pH with different acids, E. coli was found to be more tolerant in samples acidified with malic acid, followed by lactic and acetic acids. Increasing the soluble solids content from 9.4 to 11.5 °Brix showed no significant effect on the thermal tolerance of E. coli (P > 0.01). The data from this study will be useful for establishing critical limits for safe thermal processing of pH-controlled juices and similar products.