Fate of Salmonella throughout Production and Refrigerated Storage of Tahini

Abstract

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.

Complete Genome Sequences of Five Salmonella enterica Strains Used in Inoculation Cocktails in Low-Moisture Food Storage Studies

“…to survive on these foods (nuts, black pepper, and spices) in a low-moisture environment. Numerous studies on the survival of Salmonella enterica in dried foods have previously been published (1–3) using a cocktail of different strains. Here, we report the complete closed genome sequences of 5 strains commonly used in these studies, S.…”

Effect of water activity and storage of tahini on the viability of stressed Salmonella serovars

“…However, other reports revealed that Salmonella numbers in low a w products either did not change during storage or were not affected by storage temperature. Zhang et al (2017) indicated that Salmonella can survive with no change in numbers in tahini during refrigerated storage for 4 months. Additionally, no significant differences were noticed between the levels of S. Tennessee in 4 of 5 commercial brands of peanut butter stored at 4 or 22 °C.…”

“…The variation between these and the results presented in the current study may have been due to serovar differences, variation in culture cultivation procedures, product composition or the variability in the storage time of the products that was mostly compatible with anticipated shelf-life of the product. In the studies by Zhang et al (2017) and Frelka et al (2016), bacteria used were taken from solid media and were sessile cells, while in the present study bacteria used were planktonic in nature, grown in liquid media. In addition, tahini samples used in the Zhang et al (2017) study were prepared by grinding sesame seeds with olive oil in a food processor while commercial tahini samples were used in the present study.…”

“…In the studies by Zhang et al (2017) and Frelka et al (2016), bacteria used were taken from solid media and were sessile cells, while in the present study bacteria used were planktonic in nature, grown in liquid media. In addition, tahini samples used in the Zhang et al (2017) study were prepared by grinding sesame seeds with olive oil in a food processor while commercial tahini samples were used in the present study.…”

“…According to Torlak et al (2013), Salmonella did not survive roasting of sesame seeds at 110, 130, and 150 °C. However, Zhang et al (2017) reported survival of Salmonella on sesame seeds increased as a w decreased during roasting. Thus, the presence of Salmonella in tahini might be due to the ability of Salmonella to survive the roasting process if the seeds are at a low a w at the beginning of the roasting process (Zhang et al, 2017), or their presence may be due to post-heat treatment contamination from equipment, workers or the processing environment (World Health Organization, 2008;Torlak et al, 2013).…”