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2012-2015 Bacterial Pathogens on In-Shell Nuts and in Shelled Nuts and Nut Butters


Nuts and nut butters are popular foods in Canada and around the world. However, foodborne illness outbreaks of salmonellosis associated with nuts and nut butters have been reported worldwide including in Canada. Nuts are low-moisture foods of agricultural origin that can become contaminated by bacterial pathogens during primary production, harvest, processing and storage. Once nuts are contaminated, bacterial pathogens such as Salmonella can survive for long periods of time due to the low-moisture content of the nuts. Nut butters are low-moisture, high fat foods that can be contaminated by contaminated nuts or by cross-contamination during processing and/or storage. In addition, standard thermal treatments are often ineffective at eliminating Salmonella from highly contaminated nut butter products due to its ability to develop heat resistance in low-moisture, high-fat environments. Therefore, the microbial safety of nuts and nut butters remains a concern.

Considering the factors mentioned above and their relevance to Canadians, in-shell nuts, shelled nuts and nut butters were selected for targeted surveys. The purpose of the survey was to generate baseline information on the occurrence of bacterial pathogens on the surface of in-shell nuts and in shelled nuts and nut butters on the Canadian market. Over the course of this study (April 1, 2012 to March 31, 2015), a total of 2400 in-shell nut samples, 2612 shelled nut samples, and 1142 nut butter samples were collected from retail locations in 11 cities across Canada and were tested for bacterial pathogens of concern: Salmonella, Escherichia coli (E. coli) O157:H7 and Listeria monocytogenes (L. monocytogenes) (nut butters only), as well as generic E. coli. Generic E. coli is an indicator of the overall sanitation conditions throughout the food chain from production to the point of sale.

All shelled nuts (100%), nut butters (100%) and over 99.8% of in-shell nuts were found to be free of specific pathogenic bacteria tested for. E. coli O157:H7, L. monocytogenes and generic E. coli (> 100 colony forming unit (CFU)/g) were not found in any samples tested. However, Salmonella was found in five in-shell nut samples (5/2400, 0.21%) including two walnut samples (2/792, 0.25%) and three hazelnut samples (3/696, 0.43%). The Canadian Food Inspection Agency (CFIA) conducted appropriate follow-up activities including food safety investigations related to the Salmonella contaminated products. All five affected products were recalled from the Canadian market. No reported illnesses were associated with any of the Salmonella contaminated products.

The results indicate that almost all of the nut and nut butter samples appear to have been produced under Good Agricultural Practices and Good Manufacturing Practices. Sporadically, Salmonella contamination on in-shell nuts can occur.

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