Salmonella enterica serovar Choleraesuis on fresh-cut cucumber slices after reduction treatments

Modeling the Growth of Salmonella on Sliced Cucumbers as a Function of Temperature and Relative Humidity

ABSTRACT

Recent multistate outbreaks of salmonellosis linked to fresh cucumbers underscore the importance of understanding Salmonella behavior on cucumbers under different storage conditions. No validated models that describe the impact of environmental factors on the growth of Salmonella on sliced cucumbers currently exist. This study developed mathematical models to predict the growth of Salmonella on sliced cucumbers at different temperature and relative humidity (RH) conditions. Sliced cucumbers were inoculated with a four-strain cocktail of Salmonella and placed in desiccators containing a saturated salt solution to create controlled RH environments (∼15, 50, and 100% RH) at 7, 14, and 21°C for up to 120 h. Predictive models were developed by using the Baranyi and Roberts equation as a primary model, and estimated kinetic parameters were fitted into a square root (or Ratkowsky) equation for secondary models. The maximum growth rates for Salmonella on sliced cucumbers depended on temperature but not RH. The square root model for Salmonella growth was √μ= 0.0297 × (T - 6.5185), with a high R2 value (0.98). The models in this study will be useful for future microbial risk assessments and predictions of Salmonella behavior in the cucumbers to manage the risk of Salmonella on sliced cucumbers.

HIGHLIGHTS

Modeling the survival of Salmonella on whole cucumbers as a function of temperature and relative humidity

Recent multistate outbreaks of salmonellosis associated with fresh cucumbers underscore the importance of understanding Salmonella behavior on cucumbers under different conditions. This study developed mathematical models to predict the survival of four-strain cocktail of Salmonella on whole cucumbers at different temperature and relative humidity (RH) conditions. The strains were Salmonella Newport H1275 and Stanley H0558 (sprout outbreaks), Montevideo G4639 (tomato outbreak), and Saintpaul 02-517-1 (cantaloupe outbreak). Inoculated cucumbers were placed in desiccators containing saturated salt solution to create controlled RH environments (~15, 50, 100% RH) at 7, 14, and 21 °C, and enumerated at time intervals ranging from 0 to 240 h. Predictive models were developed using Baranyi and Roberts equation as a primary model and estimated kinetic parameters were fitted into a polynomial equation for secondary models. Reduced model polynomial equations which describe the maximum death rate and the log reduction of Salmonella on whole cucumber as a function of temperature and RH had high R² values (>0.95). Validation results verified the performance and reliability of the predictive models. The models in this study will be useful for future microbial risk assessments and predictions of Salmonella behavior in the cucumbers to manage the risk of Salmonella on whole cucumbers.

The Impact of N2-Assisted High-Pressure Processing on the Microorganisms and Quality Indices of Fresh-Cut Bell Peppers

This work aimed to evaluate the effects of N₂-assisted high-pressure processing (HPP, 400 MPa/7.5 min and 500 MPa/7.5 min) on the microorganisms and physicochemical, nutritional, and sensory characteristics of fresh-cut bell peppers (FCBP) during 25 days of storage at 4 °C. Yeasts and molds were not detected, and the counts of total aerobic bacteria were less than 4 log₁₀ CFU/g during storage at 4 °C. The total soluble solids and L* values were maintained in HPP-treated FCBP during storage. After the HPP treatment, an 18.7–21.9% weight loss ratio and 54–60% loss of hardness were found, and the polyphenol oxidase (PPO) activity was significantly inactivated (33.87–55.91% of its original activity). During storage, the weight loss ratio and PPO activity of the samples increased significantly, but the hardness of 500 MPa/7.5 min for treated FCBP showed no significant change (9.79–11.54 N). HPP also effectively improved the total phenol content and antioxidant capacity of FCBP to 106.69–108.79 mg GAE/100 g and 5.76–6.55 mmol Trolox/L; however, a non-negligible reduction in total phenols, ascorbic acid, and antioxidant capacity was found during storage. Overall, HPP treatments did not negatively impact the acceptability of all sensory attributes during storage, especially after the 500 MPa/7.5 min treatment. Therefore, N₂-assisted HPP processing is a good choice for the preservation of FCBP.

Growth and Survival of Listeria monocytogenes and Salmonella on Whole and Sliced Cucumbers

Cucumbers were associated with four multistate outbreaks of Salmonella in the United States between 2013 and 2016. This study evaluated the fate of Listeria monocytogenes and Salmonella on whole and sliced cucumbers at various storage temperatures. Cucumbers were inoculated with five-strain cocktails of L. monocytogenes or Salmonella, air dried, and stored at 23 ± 2, 4 ± 2, and -18 ± 2°C. Whole and sliced cucumber samples were enumerated on nonselective and selective media at 0, 0.21, 1, 2, 3, and 4 days (23 ± 2°C); 0, 1, 2, 3, 7, 14, and 21 days (4 ± 2°C); and 0, 7, 28, 60, 90, and 120 days (-18 ± 2°C). For Salmonella, additional time points were added at 8 and 17 h (23 ± 2°C) and at 17 h (4 ± 2°C). Population levels were calculated for whole (CFU per cucumber) and sliced (CFU per gram) cucumbers. Both pathogens grew on whole and sliced cucumbers held at ambient temperatures. At 23 ± 2°C, L. monocytogenes and Salmonella populations significantly increased on whole (2.3 and 3.4 log CFU per cucumber, respectively) and sliced (1.7 and 3.2 log CFU/g, respectively) cucumbers within 1 day. Salmonella populations significantly increased on whole and sliced cucumbers after only 5 h (2.1 log CFU per cucumber and 1.5 log CFU/g, respectively), whereas L. monocytogenes populations were not significantly different on whole and sliced cucumbers at 5 h. L. monocytogenes and Salmonella populations survived up to 21 days on refrigerated whole and sliced cucumbers. At 4 ± 2°C, L. monocytogenes populations significantly increased on whole (2.8 log CFU per cucumber) and sliced (2.9 log CFU/g) cucumbers, whereas Salmonella populations significantly decreased on whole (0.6 log CFU per cucumber) and sliced (1.3 log CFU/g) cucumbers over 21 days. Both pathogens survived on frozen whole and sliced cucumbers for at least 120 days. The ability of L. monocytogenes and Salmonella to grow on whole and sliced cucumbers in short amounts of time at ambient temperatures, and to survive on whole and sliced cucumbers past the recommended shelf life at refrigeration temperatures, highlights the need to reduce the likelihood of contamination events throughout the cucumber supply chain.