Survival of Salmonella and Enterococcus faecium in high fructose corn syrup and honey at room temperature (22 °C)

The effect of emulsifier type and oil fraction on Salmonella Typhimurium growth and thermal inactivation in oil-in-water emulsion

High water activity oil-in-water emulsions can promote survival and growth of Salmonella Typhimurium. Nevertheless, the precise effect of emulsifier type and oil content on bacterial growth and inactivation is not fully understood. Here, emulsions were prepared using different emulsifiers (Tween 20, Tween 80, and Triton X-100) and different oil fractions (20%, 40%, and 60% (v/v)). TSB (control), emulsifier solutions, and emulsions were inoculated with S. Typhimurium. Bacterial growth rate was measured at 7, 22, and 37°C, whereas thermal inactivation was performed at 55°C. Growth and inactivation data was fitted into Logistic and Weibull models, respectively. At an incubation temperature of 37°C, the presence of high amount of oil (60%) in Tween 20 and Triton X stabilized emulsions extended the lag phase (5.83 ± 2.20 and 9.43 ± 1.07 h, respectively, compared to 2.28 ± 1.54 h for TSB, p < 0.05), whereas individual emulsifiers had no effect on growth behavior compared to TSB. This effect was also prevalent but attenuated at 22°C, whereas no growth was observed at 7°C. In thermal inactivation, we observed protective effect in Tween 80 and Triton X-100 solutions, where time required for five-log reduction was 1914.70 ± 706.35 min and 795.34 ± 420.09 min, respectively, compared to 203.89 ± 10.18 min for TSB (p < 0.05). Interestingly, the presence of high amount of oil did not offer protective effect during thermal inactivation. We hypothesize that oleic acid in Tween 80 and lower hydrophobicity value of Triton X-100 help maintain membrane integrity and improve the resistance of bacteria to heat inactivation.

Food Handling Practices for Apple Drying in Home Kitchens in the United States: A Survey

ABSTRACT

Fruit drying has traditionally received little food safety attention in spite of Salmonella outbreaks and recalls involving low-moisture foods. This study was conducted to assess the food safety implications during the home drying process, with dried apples as an example. A cohort of home apple dryers (n = 979) participated in an online survey through Qualtrics XM in May 2021. The results showed that participants' knowledge of safe food handling practices regarding dried fruit was low. On average, participants used only 8 of 18 identified food safety practices during apple drying. The survey revealed inadequate frequency of hand washing during apple preparation, potential points of cross-contamination from kitchen tools, lack of hurdle technology without a pretreatment step, failure to incorporate a thermal kill step during drying, and a lack of objective measurements to ensure that target parameters are attained. Participants mainly pretreated apples for sensory improvement instead of microbial reduction. When presented with some benefits of pretreatment, participants who did not pretreat their apples considered doing so to kill bacteria. The use of safe food handling practices differed within demographic groups. Participants 18 to 39 years old (mean = 7.47; 95% confidence interval [CI] = 7.26, 7.67) and 40 to 59 years old (mean = 7.43; 95% CI = 7.16, 7.70) reported using fewer safe practices than did those >60 years old (mean = 8.49; 95% CI = 8.22, 8.75), and participants who identified as male (mean = 7.38; 95% CI = 7.16, 7.60) reported using fewer safe practices than did those identifying as female (mean = 7.92; 95% CI = 7.74, 8.11). The findings of this study provide food handling data to support the development of more accurate food safety risk assessment models and to guide the development of food safety education for consumers who dehydrate produce in the home.

HIGHLIGHTS

Control of Salmonella in low-moisture foods: Enterococcus faecium NRRL B-2354 as a surrogate for thermal and non-thermal validation

Salmonella has been implicated in multiple foodborne outbreaks and recalls associated with low water activity foods (La_wF). To verify the effectiveness of a process against Salmonella in La_wF, validation using a nonpathogenic surrogate strain is essential. Enterococcus faecium NRRL B-2354 strain has been used as a potential surrogate of Salmonella in different processing of La_wF. However, the survival of Salmonella and E. faecium in La_wF during food processing is a dynamic function of a_w, food composition and structure, processing techniques, and other factors. This review assessed pertinent literature on the thermal and non-thermal inactivation of Salmonella and its presumable surrogate E. faecium in various La_wF and provided an overview of its suitibility in different La_wF. Overall, based on the D-values, survival/reduction, temperature/time to obtain 4 or 5-log reductions, most studies concluded that E. faecium is a suitable surrogate of Salmonella during La_wF processing as its magnitude of resistance was slightly greater or equal (i.e., statistical similar) as compared to Salmonella. Studies also showed its unsuitability which either does not provide a proper margin of safety or being overly resistant and may compromise the quality and organoleptic properties of food. This review provides useful information and guidance for future validation studies of La_wF.