Inhibition of Listeria monocytogenes and Clostridium botulinum in Uncured Shredded Pork and Turkey Packaged Under Reduced Oxygen Conditions.

Cooked, uncured meat products packaged under reduced oxygen packaging conditions require the control of anaerobic and facultative anaerobic pathogens if they are held at temperatures greater than 3°C at retail or consumer level. The objective of this study was to determine the inhibition of Listeria monocytogenes and Clostridium botulinum in cooked, uncured shredded turkey and pork formulated with synthetic or clean-label antimicrobials. Treatments of shredded meat products were prepared with or without antimicrobials using turkey thigh or breast that were cooked to 85°C, shredded, and chilled before inoculation with the target pathogen. L. monocytogenes inoculated samples were stored at 7.2°C, whereas C. botulinum samples were stored at 12.8°C; triplicate samples were assayed every 2 weeks. In the first set of experiments, L. monocytogenes populations increased 2 to 3 logs within 2 weeks of storage at 7.2°C in both meat control treatments without antimicrobials and in pork with 4% lactate-diacetate blend (LD). A 1-log increase was observed in turkey with 4% LD and Pork with 2% cultured dextrose-vinegar-rosemary (CDVR) under the same storage conditions; a 1-log increase was observed in turkey with CDVR at 4 weeks. The second set of experiments tested the effect of pH reduction (to less than 5.5 by the addition of 0.5% citric acid) in combination with 2% CDVR when added to the brine precook or postcook during shredding. Populations of L. monocytogenes increased 4-log within 2 and 4 weeks at 7.2°C for the control turkey and pork formulations, respectively. No growth was observed in 12 weeks for any antimicrobial CDVR-CA treatments regardless of how antimicrobial was added. Similarly, botulinum toxin was detected in both control treatments at week 2 at 12.8°C, but no toxicity was observed in either antimicrobial treatment through 12 weeks. These data suggest that a combination of 2% cultured dextrose-vinegar-rosemary extract plus 0.5% citric acid to reduce pH inhibits the growth of L. monocytogenes and toxin production of C. botulinum in uncured shredded turkey and pork products stored under mild temperature abuse conditions for up to 12 weeks in reduced oxygen packaging.

Predictive model for growth of Clostridium botulinum from spores during cooling of cooked ground chicken.

Cooking temperature of poultry meat is typically inadequate to inactivate the heat resistant spores of Clostridium botulinum. The purpose of this study is to develop a predictive model for C. botulinum during cooling of cooked ground chicken. Cooked chicken was inoculated with a cocktail of five strains of proteolytic C. botulinum type A and five strains of proteolytic C. botulinum type B to yield a final spore concentration of approximately 2 log CFU/g. The growth of C. botulinum was determined at constant temperatures from 10 to 46 °C. Dynamic temperature experiments were performed with continued cooling from 54.4 to 4.4 °C or 7.2 °C in mono- or bi-phasic cooling profiles, respectively. The Baranyi primary model was used to fit growth data and the modified Ratkowsky secondary model was used to fit growth rates with respect to temperature. The primary models fitted the growth data well (R2 values ranging from 0.811 to 0.988). The R2 and root mean square error (RMSE) of the modified Ratkowsky secondary model were 0.95 and 0.06, respectively. Out of 11 prediction error values calculated in this study, ten were within the limit of acceptable prediction zone (-1.0 to 0.5), indicating a good fit of the model. The predictive model will assist institutional food service operations in determining the safety of cooked ground chicken subjected to different cooling periods.

Effect of Equilibrated pH and Indigenous Spoilage Microorganisms on the Inhibition of Proteolytic Clostridium botulinum Toxin Production in Experimental Meals under Temperature Abuse.

Clostridium botulinum is a foreseeable biological hazard in prepared refrigerated meals that needs to be addressed in food safety plans. The objective of this study was to evaluate the effect of product composition and storage temperature on the inhibition of botulinum toxin formation in nine experimental meals (meat, vegetable, or carbohydrate based). Treatments were inoculated with proteolytic C. botulinum, vacuum packaged, cooked at 90°C for 10 min, and assayed for botulinum toxin in samples stored at 25°C for up to 96 h for phase 1, or at 25°C for 12 h and then transferred to 12.5°C for up to 12 and 6 weeks in phases 1 and 2, respectively. For phase 1, none of the treatments (equilibrated pH 5.8) supported toxin production when stored at 25°C for 48 h, but toxin production was observed in all treatments at 72 h. For the remaining experiments with storage at 12.5°C, toxin production was dependent on equilibrated pH, storage time, and growth of indigenous spoilage microorganisms. In phase 1, no gross spoilage and no botulinum toxin was detected for any treatment (pH ≤5.8) stored at 12.5°C for 12 weeks. In phase 2, gross spoilage varied by commodity, with the brussels sprouts meal with pH 6.5 showing the most rapid spoilage within 2 weeks and botulinum toxin detected at 5 and 6 weeks for the control and cultured celery juice treatments, respectively. In contrast, spoilage microbes decreased the pH of a pH 5.9 beef treatment by 1.0 unit, potentially inhibiting C. botulinum through 6 weeks at 12.5°C. None of the other treatments with pH 5.8 or below supported toxin production or spoilage. This study provides validation for preventive controls in refrigerated meals. These include equilibrated product pH and storage temperature and time to inhibit toxin formation by proteolytic C. botulinum, but the impact of indigenous microflora on safety and interpretation of challenge studies is also highlighted.

Effect of Cultured Celery Juice, Temperature, and Product Composition on the Inhibition of Proteolytic Clostridium botulinum Toxin Production.

Clostridium botulinum may be of concern in prepared refrigerated meals, for which strict cold chain management cannot be guaranteed. This study evaluated the effect of temperature, product composition, and cultured celery juice powder (CCJP) as a source of nitrite on the inhibition of botulinum toxin formation in two experimental (meat- and vegetable-based) prepared meals. Data obtained from the challenge study were compared with a published mathematical model to determine whether the model is fail-safe with regard to the tested meals. Treatments were inoculated with proteolytic C. botulinum, vacuum packaged, cooked at 90°C for 10 min, and assayed for botulinum toxin at appropriate intervals in samples stored at 10, 15, or 20°C for up to 8 weeks. None of the treatments stored at 10°C for 8 weeks supported toxin production by proteolytic C. botulinum. The addition of CCJP delayed toxin production by 1 and 3 weeks in cauliflower potatoes and in Dijon pork, respectively, stored at 15°C. Toxin production was delayed by 1 week at 20°C when CCJP was added to the cauliflower potatoes. This study found that the predictive model was fail-safe but was overly conservative for the experimental meals described. Finally, this study confirms that product composition, the addition of nitrite via CCJP, storage time, and temperature play important roles in the inhibition of toxin formation by proteolytic C. botulinum.

Growth of Listeria monocytogenes within a caramel-coated apple microenvironment.

UNLABELLED: A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0.80) are too low to support Listeria growth. In this study, Granny Smith apples were inoculated with approximately 4 log10 CFU of L. monocytogenes (a cocktail of serotype 4b strains associated with the outbreak) on each apple's skin, stem, and calyx. Half of the apples had sticks inserted into the core, while the remaining apples were left intact. Apples were dipped into hot caramel and stored at either 7°C or 25°C for up to 11 or 28 days, respectively. Data revealed that apples with inserted sticks supported significantly more L. monocytogenes growth than apples without sticks under both storage conditions. Within 3 days at 25°C, L. monocytogenes populations increased >3 log10 in apples with sticks, whereas only a 1-log10 increase was observed even after 1 week for caramel-coated apples without sticks. When stored at 7°C, apples with sticks exhibited an approximately 1.5-log10 increase in L. monocytogenes levels at 28 days, whereas no growth was observed in apples without sticks. We infer that insertion of a stick into the apple accelerates the transfer of juice from the interior of the apple to its surface, creating a microenvironment at the apple-caramel interface where L. monocytogenes can rapidly grow to levels sufficient to cause disease when stored at room temperature. IMPORTANCE: Neither caramel nor apples are a food where the pathogenic bacterium Listeria monocytogenes should grow, as caramel does not contain enough free water and apples are too acidic. Caramel-coated apples, however, were recently linked to a deadly outbreak of listeriosis. We hypothesized that inserting a stick into the apple releases juice to the interface between the apple and caramel, providing a more hospitable environment than either component alone. To test this hypothesis, apples were inoculated with L. monocytogenes prior to caramel dipping. Some apples had sticks inserted into them before dipping, while others did not. No growth of L. monocytogenes occurred on refrigerated caramel apples without sticks, whereas slow growth was observed on refrigerated caramel apples with sticks. In contrast, significant pathogen growth was observed within 3 days at room temperature on caramel apples with sticks inserted. Food producers should consider interfaces between components within foods as potential niches for pathogen growth.

Inhibition of Listeria monocytogenes in deli-style turkey breast formulated with cultured celery powder and/or cultured sugar-vinegar blend during storage at 4°c.

Fermentation-derived nitrite (NO2) from vegetable sources is increasingly used as a "clean label" alternative to conventional NaNO2. Previous results suggested that processed meats cured with NO2 derived from a "natural" source had lower antimicrobial activity than did meats produced with chemical NaNO2; however, the differences were likely due to NO2 concentration rather than source. The objective of this study was to compare the antilisterial properties of traditional and clean label alternative curing approaches when combined with antimicrobials in deli-style turkey. Listeria monocytogenes inhibition by NO2 from synthetic and natural sources was validated in deli-style turkey (73 to 74% moisture, 1.8% salt, pH 6.4). Products were prepared with 0, 80, or 120 mg/kg NO2 using purified NaNO2 or cultured celery powder. Additional treatments were supplemented with 3.8% lactate-diacetate blend (LD) or 1% cultured sugar-vinegar blend (DF). Sliced cooked products were surface inoculated with L. monocytogenes at 3 log CFU/g, vacuum packaged, and stored at 4°C for 12 weeks. Results revealed an average 2.4-log increase in L. monocytogenes at 3 weeks in the control without antimicrobials, a 1.3-log increase at 4 weeks for both 80 mg/kg NO2 treatments, and a 1.5-log increase at 6 weeks for the 120 mg/kg NO2 treatments. No significant difference (P > 0.05) in growth inhibition was found between NO2 sources when equivalent concentrations were added. In uncured turkey with 3.8% LD or 1% DF, growth was delayed until 6 weeks, whereas supplementation with LD or DF and 80 mg/kg NO2 from either source delayed listerial growth through 12 weeks. This study confirmed that the concentration of NO2, rather than the source, is a primary factor in enhancing the safety of ready-to-eat meats. Both conventional NO2 treatments and a clean label solution consisting of a fermentation-derived antimicrobial combined with 80 mg/kg naturally derived NO2 inhibited L. monocytogenes through 12 weeks of storage at 4°C.