Influence of peroxyacetic acid concentration, temperature, pH, and treatment time on antimicrobial efficacy against Salmonella on chicken wings.

Peroxyacetic acid (PAA) is commonly used during poultry processing to reduce the prevalence of Salmonella on carcasses and parts. Wash solutions containing PAA are used at varying concentrations during processing and processors use internally validated practices that best suit the needs of the individual establishment. This study was conducted to determine how temperature, pH, and contact time in combination with PAA concentration can affect the survival of Salmonella on poultry. The effectiveness of PAA in reducing the population of Salmonella on chicken wings was dependent on the concentration and temperature of the PAA solutions. The pH or contact time had no effects (P > 0.05) on total Salmonella or Salmonella Infantis reduction (log CFU/mL). Treatment with 0 ppm PAA at 27°C did not reduce (P > 0.05) total Salmonella or Salmonella Infantis compared to the inoculated, untreated control; in contrast, treatment at 4°C and 0 ppm PAA reduced (P < 0.05) total Salmonella and Salmonella Infantis. Treatments applied at 4°C significantly reduced (P < 0.05) total Salmonella at 50, 200, and 500 ppm PAA, compared to treatment at 27°C among the same PAA concentration. The population of Salmonella Infantis was significantly reduced (P < 0.05) at 4°C with 0, 50, 200, 500, and 1,000 ppm PAA among the same PAA concentration, compared to treatment at 27°C. Treatment conditions, such as temperature, can impact the effectiveness of PAA used as an antimicrobial treatment during poultry processing, and the results from this study can provide useful insights that could assist poultry processors to effectively incorporate PAA into antimicrobial intervention systems.

Predictive modeling of thermal inactivation of non-O157 Shiga toxin-producing Escherichia coli in ground beef with varying fat contents.

A mathematical model to predict the thermal inactivation of non-O157 Shiga toxin-producing Escherichia coli (STEC) in ground beef was developed, with temperature and fat content of ground beef as controlling factors. Survival curves for a cocktail of non-O157 STEC strains in ground beef at four temperatures (55, 60, 65, and 68 °C) and six fat levels (5, 10, 15, 20, 25, and 30%) were generated. Nine primary models-log-linear, log-linear with tail, biphasic, sigmoidal, four-factor sigmoidal, Baranyi, Weibull, mixed Weibull, and Gompertz-were tested for fitting the survival curves. Primary modeling analysis showed the Weibull model had the highest accuracy factor and Akaike's weight, making it the best-fitting model. The parameters of the Weibull model were estimated using a nonlinear mixed, and response surface modeling was used to develop a second-order polynomial regression to estimate the impact of fat in ground beef and cooking temperature on the heat resistance of non-O157 STEC strains. The secondary model was successfully validated by comparing predicted lethality (log10 CFU/g) with the observed values for ground beef containing 10 and 27% fat at 58 and 62 °C. Process lethality obtained from experimental data was within the prediction interval of the predictive model. The developed model will assist the food industry in estimating the appropriate time and temperature required for cooking ground beef to provide adequate protection against STEC contaminants.

Listeria monocytogenes loss of cultivability on carrot is associated with the formation of mesosome-like structures.

Raw carrot is known to have antimicrobial activity against Listeria monocytogenes, but the mechanism of action has not been fully elucidated. In this study, we examined carrot antilisterial activity against several strains of Listeria species (including L. grayi, L. innocua, L. seeligeri, and L. welshimeri) and L. monocytogenes. A representative strain of L. monocytogenes was subsequently used for further characterizing carrot antilisterial activity. Exposure to fresh-cut carrot for 15 min resulted in a similar loss of cultivability, ranging from 2.5 to 4.7 log units, across all Listeria strains evaluated. L. monocytogenes recovered from the fresh-cut surface of different raw carrots was 1.6 to 4.1 log lower than levels obtained from paired boiled carrot samples with abolished antilisterial activity. L. monocytogenes levels recovered from fresh-cut carrot were 2.8 to 3.1 log lower when enumerated by culture-dependent methods than by the culture-independent method of PMAxx-qPCR, a qPCR assay that is performed using DNA pre-treated to selectively sequester DNA from cells with injured membranes. These results suggested that L. monocytogenes loss of cultivability on fresh-cut carrot was not associated with a loss of L. monocytogenes cell membrane integrity and putative cell viability. Transmission electron microscopy imaging revealed that L. monocytogenes rapidly formed mesosome-like structures upon exposure to carrot fresh-cut surface but not upon exposure to boiled carrot surface, suggesting there may be an association between the formation of these mesosome-like structures and a loss of cultivability in L. monocytogenes. However, further research is necessary to conclude the causality of this association.

Effect of a carrageenan/chitosan coating with allyl isothiocyanate on microbial spoilage and quality of chicken breast.

Approximately 3.7% of poultry meat is lost due to spoilage each year in the United States. The objective of this study was to determine the efficacy of a layered carrageenan/chitosan coating in combination with an application of two concentrations of allyl isothiocyanate (AITC) against lactic acid bacteria, aerobic bacteria, and yeast and mold during storage of chicken breast for 21 d. Additionally, the rancidity, color, and pH of the chicken breast as indicators of non-microbial quality were evaluated. The combination of carrageenan/chitosan coating with 20 and 200 ppm AITC reduced (P ≤ 0.05) yeast and mold populations by 3 log10 CFU/g at d 21 compared to the untreated control. The carrageenan/chitosan coating with 20 and 200 ppm AITC delayed aerobic spoilage by 3 and 12 d, respectively, compared to the untreated control; aerobic bacteria populations on the samples treated with 200 ppm AITC remained below the threshold for spoilage (∼6 log10 CFU/g) for the duration of storage. The pH of the 20 ppm and 200 ppm AITC-treated chicken breast was unaltered (P > 0.05) at the end of storage and was lower than the pH of the untreated and coating-only-treated control chicken breast at d 18 through the end of storage (P ≤ 0.05). The application of the coating alone did not (P > 0.05) affect L*, a*, and b* values of the chicken breast at the end of storage compared to the uncoated control. The carrageenan/chitosan coating with 20 and 200 ppm AITC prevented decreases in the lightness (L* values) of the chicken breast at the end of storage (P ≤ 0.05) compared to the control and coating-only-treated samples. The coating alone or with AITC did not (P > 0.05) impact the rancidity of the chicken breast over the 21-d storage period, thus showing potential to be used as antimicrobial packaging to increase shelf life of fresh poultry.

Dynamics of Listeria monocytogenes and the microbiome on fresh-cut cantaloupe and romaine lettuce during storage at refrigerated and abusive temperatures.

Listeria monocytogenes (Lm) outbreaks and recalls associated with fresh produce in recent years have heightened concerns and demands from industry and consumers to more effectively mitigate the contamination risk of this foodborne pathogen on fresh produce. In this study, the growth of Lm and indigenous bacteria on fresh-cut cantaloupe and romaine lettuce held at refrigerated (4 °C) and abusive (10-24 °C) temperatures was determined by both culture dependent and independent methods. Composition and dynamics of bacterial communities on Lm inoculated and non-inoculated samples were analyzed by 16S rRNA high-throughput sequencing. Fresh-cut cantaloupe provided favorable growth conditions for Lm proliferation (1.7 and >6 log increase at refrigerated and abusive temperatures, respectively) to overtake indigenous bacteria. The Lm population also increased on fresh-cut lettuce, but the growth rate was lower than that of the total mesophilic bacteria, resulting in 0.4 and >2 log increase at refrigerated and abusive temperatures. Microbial diversity of fresh-cut cantaloupe was significantly lower than that of fresh-cut romaine lettuce. The Shannon index of microbial communities on cantaloupe declined after storage, but it was not significantly changed on lettuce samples. Shifts in the bacterial microbiome on cantaloupe were mainly affected by Lm inoculation, while both inoculation and storage temperature played significant roles on lettuce bacterial communities. Multiple indigenous bacteria, including Leuconostoc and Weissella spp., were negatively correlated to Lm abundance on romaine lettuce, and were determined by bioassay as potential anti-listerial species. Data derived from this study contribute to better understanding of the relationship between Lm and indigenous microbiota on fresh-cut produce during storage.

Draft Genome Sequences of Two Salmonella Strains from the SARA Collection, SARA64 (Muenchen) and SARA33 (Heidelberg), Provide Insight into Their Antibiotic Resistance.

The Salmonella enterica strains that are representatives of the S. enterica serovar Typhimurium complex in reference collection A (SARA) are closely related but exhibit differences in antibiotic resistance, which could have public health consequences. To better understand the mechanisms behind these resistances, we sequenced the genomes of two multidrug-resistant strains: SARA64 (Muenchen) and SARA33 (Heidelberg).