Sesame seeds used in sesame seed products undergo a roasting step that should be sufficient to inactivate Salmonella spp.
Post-processing contamination can occur due to poor hygiene. Some foods, such as canned, retorted, cooked or baked products receive a further heat treatment step which will mitigate post-processing contamination.
Key risk factors associated with on-farm production of sesame seeds include the quality of the irrigation water, use of untreated manure as fertiliser and animal access to the crop.
Plants may be dried unprotected in the open air and in some cases the product is left to dry directly on the ground.
Risk factors associated with this include the cleanliness of the drying area and the presence of animals and birds that can shed or transmit Salmonella spp.
Sesame seeds used in sesame seed products undergo a roasting step that should be sufficient to inactivate Salmonella spp. However, contamination of sesame seed products can occur after the heat treatment step due to poor hygiene during subsequent grinding of the sesame seeds, slicing, packaging and transport. The presence of both high lipid content and low water activity in sesame seed products enables Salmonella spp. to survive in these products for long periods.
Therefore, sesame seeds and sesame seed products that are not further processed after roasting (for example retorting or cooking) have the potential to be contaminated with Salmonella spp. One recent example would be Tahini with issues in the USA and UK.
Results of this study (https://www.sciencedirect.com/science/article/pii/S0168160513001554) demonstrated that the standard roasting process is sufficient to inactivate Salmonella in sesame seeds and low water activity of tahini prevents microbial growth, but its composition allows Salmonella to survive for at least 16 weeks. Therefore, prevention of cross-contamination after roasting is crucial for food safety.
Illness associated with consumption of sesame seeds and sesame seed products contaminated with Salmonella spp.
There have been a number of salmonellosis outbreaks associated with consumption of sesame seeds and sesame seed products 1990 – 2016:
• Outbreak in the United States in 2013 – 16 cases of salmonellosis linked to consumption of tahini sesame paste imported from Turkey. Both Salmonella Montevideo (4 cases) and Salmonella Mbandaka (12 cases) were associated with this outbreak. Both outbreak strains were isolated from the product (CDC 2013).
• Outbreak in New Zealand in 2012 – 16 cases of salmonellosis linked to consumption of hummus made from tahini sesame paste imported from Turkey. Salmonella Montevideo (12 cases), Salmonella Mbandaka (3 cases) and Salmonella Maastricht (1 case) were associated with this outbreak. All three outbreak strains were detected in unopened containers of tahini. The tahini associated with this outbreak was imported from the same company in Turkey as that implicated in the United States outbreak described above (CDC 2013; Paine et al. 2014).
• Three outbreaks across Australia and New Zealand in 2002/2003 – with a total of 68 cases of Salmonella Montevideo infection linked to consumption of hummus and tahini imported from Egypt and Lebanon. The outbreak strain was isolated from the sesame seed products implicated in the outbreaks (Unicomb et al. 2005).
• International outbreak in 2001 – Salmonella Typhimiurium DT104 infection linked to consumption of halva imported from Turkey. There were 27 cases in Sweden and 23 cases in Australia. The outbreak strain was isolated from a number of halva products manufactured in Turkey (OzFoodNet 2001; Brockmann 2001; de Jong et al. 2001).
Prevalence of Salmonella spp. in sesame seeds and sesame seed products
A search of the scientific literature via Web of Science, PubMed, Scopus, CAB abstracts and other publications during the period 1990 – April 2016 identified that data on the prevalence of Salmonella spp. in sesame seeds and sesame seed products is limited:
• Survey in Germany in 2001 – Salmonella spp. were isolated from 11.1% of sesame seeds and sesame seed products (halvah and sesame paste) (n=99) collected at retail (Brockmann et al. 2004).
• Survey in the United States in 2006/2009 – Salmonella spp. were isolated from 11.3% of imported shipments of sesame seeds (n=177) (Van Doren et al. 2013a).
• Survey in the United States in 2010 – Salmonella spp. were isolated from 9.9% of imported shipments of sesame seed (n=233) (Van Doren et al. 2013b).
• Survey in the United Kingdom in 2007/2008 – Salmonella spp. were isolated from 1.7% of sesame seeds (n=771) collected at retail (Willis et al. 2009).
There have also been over 150 RASFF Alerts in Europe in 2018 for Sesame Seeds or Sesame Seed products with Salmonella identified with products from Nigeria, Sudan, Egypt, Burkina Faso, India and Uganda