Salmonella can survive in low-moisture, high-protein, and high-fat foods for several years. Despite nationwide outbreaks and recalls due to the presence of Salmonella in low-moisture foods, information on thermal inactivation of Salmonella in these products is limited. This project evaluated the impact of water activity (a), temperature, and food composition on thermal inactivation of Salmonella enterica serovar Agona in defined high-protein and high-fat model food matrices. Each matrix was inoculated with Salmonella Agona and adjusted to obtain a target a, ranging from 0.50 to 0.98. Samples were packed into aluminum test cells and heated (52 to 90°C) under isothermal conditions. Survival of Salmonella Agona was detected on tryptic soy agar with 0.6% yeast extract. Complex influences by food composition, a, and temperature resulted in significantly different ( P < 0.05) thermal resistance of Salmonella for the conditions tested. It was estimated that the same point temperatures at which the D-values of the two matrices at each a (0.63, 0.73, 0.81, and 0.90) were identical were 79.48, 71.28, 69.62, and 38.42°C, respectively. Above these temperatures, the D-values in high-protein matrices were larger than the D-values in high-fat matrices at each a. Below these temperatures, the inverse relationship was observed. A correlation between temperature and a existed on the basis of the level of fat or protein in the food, showing that these compositional factors must be accounted for when predicating thermal inactivation of Salmonella in foods.
Tahini, a low-moisture food that is made from sesame seeds, has been implicated in outbreaks of salmonellosis. In this study, the fate of Salmonella was determined through an entire process for the manufacture of tahini, including a 24-h seed soaking period before roasting, subsequent grinding, and storage at refrigeration temperature. Salmonella populations increased by more than 3 log CFU/g during a 24-h soaking period, reaching more than 7 log CFU/g. Survival of Salmonella during roasting at three temperatures, 95, 110, and 130°C, was assessed using seeds on which Salmonella was grown. Salmonella survival was impacted both by temperature and the water activity (a) at the beginning of the roasting period. When roasted at 130°C with a high initial a (≥0.90) and starting Salmonella populations of ∼8.5 log CFU/g, populations quickly decreased below detection limits within the first 10 min. However, when the seeds were reduced to an a of 0.45 before roasting at the same temperature, 3.5 log CFU/g remained on the seeds after 60 min. In subsequent storage studies, seeds were roasted at 130°C for 15 min before processing into tahini. For the storage studies, tahini was inoculated using two methods. The first method used seeds on which Salmonella was first grown before roasting. In the second method, Salmonella was inoculated into the tahini after manufacture. All tahini was stored for 119 days at 4°C. No change in Salmonella populations was recorded for tahini throughout the entire 119 days regardless of the inoculation method used. These combined results indicate the critical importance of a during a roasting step during tahini manufacture. Salmonella that survive roasting will likely remain viable throughout the normal shelf life of tahini.
Fruit drying has traditionally received little food safety attention in spite of Salmonella outbreaks and recalls involving low-moisture foods. This study aimed to assess the food safety implications during the home drying process, using 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’ food handling regarding dried fruit was low. Participants, on average, practiced only eight of 18 identified food safety practices during apple drying. The survey revealed inadequate frequency of handwashing during apple preparation, potential points of cross-contamination from kitchen tools, a lack of hurdle technology without a pre-treatment 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 pre-treated apples for sensory improvement instead of microbial reduction. When presented with some benefits of pre-treatment, participants who did not pre-treat their apples considered doing so to kill bacteria. Level of safe food handling differed within demographic groups. Participants aged 18-39 years old (mean=7.47; 95% CI=7.26, 7.67) and 40-59 years old (mean=7.43; 95% CI=7.16, 7.70) reported less safe practices than those older than 60 years old (mean=8.49; 95% CI=8.22, 8.75), and participants who identified as males (mean= 7.38; 95% CI=7.16, 7.60) reported lower mean practices than females (mean= 7.92; 95% CI=7.74, 8.11). The findings of this study can provide handling practice data to support the development of more accurate food safety risk assessment models, as well as to guide the development of food safety education for home produce dehydrating consumers.
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