Whether they’re sprinkled on top of a salad, mixed into brownie batter or added as the star ingredient in a granola bar; nuts and seeds tend to find their way into many food products. However, it is vital for food manufacturers to ensure the safety of these items in their products. Tree nuts such as almonds, hazelnuts, pine nuts, pistachios, macadamia nuts, pecans, walnuts and peanuts have been identified as a vehicle for foodborne pathogens, including Enterohemorrhagic E. coli (EHEC), Listeria monocytogenes and Salmonella. Moreover, seeds such as sesame seeds, sunflower seeds and pumpkin seeds have been recently linked to bacterial pathogens. For example, in May 2016, almost 100 products were recalled due to Listeria contamination in sunflower seeds. Salmonella also appears to be of concern in nuts, as it has been associated with many outbreaks and recalls in recent years.

The water activity of nuts is too low to support bacterial growth, but pathogens can persist for prolonged periods of time in the dry state with slow or no decline. These pathogens can cause foodborne diseases at very low levels. As such, the documented cause of many recalls has been the potential contamination of nuts or products containing nuts.  

Nuts can become contaminated with pathogens in the orchards or on farms, during postharvest storage and handling or during processing. Irrigation water, rainfall or water introduced during processing may also spread the contaminants into manufacturing facilities. A comprehensive Environmental Monitoring Program (EMP) should be implemented to monitor the processing, handling and packaging environments to prevent product recontamination. Processors should also segregate areas in the facility to prevent contamination from raw to finished product areas after the lethality step.

Processors should also consider EHEC, L. monocytogenes and Salmonella in their food safety plan. Studies have shown that Salmonella and EHEC become more heat-resistant in a dry state. So, while thermal processes are commonly used for finished products, they may not kill the pathogens. Inactivation treatments should be validated to show that pathogens are effectively controlled. Oil roasting, dry roasting, hot water pasteurization, steam pasteurization, hot water blanching, propylene oxide (PPO) and ethylene oxide are some of the technologies processors use that fall into this category.

The Food Safety Modernization Act (FSMA) final rule requires food facilities to implement preventive controls and keep documentation showing they are verified and effective. Manufacturers must determine key requirements, including an analysis of hazards and risk-based preventive controls. Critical processing limits can be established based on published data or in-plant validation studies. The Almond Board of California (ABC) published the processing parameters for oil roasting and PPO treatment of almonds. Although these guidelines may be used as a reference point, they should not be directly applied to all nut types and processes.

Similarly, ABC has developed industry guidelines for the thermal processing of almonds using Enterococcus faecium NRRL B-2354, a surrogate culture for Salmonella. It is important that an appropriate surrogate culture with known heat resistance is identified for each specific type of process and nut. Recent studies showed that E. faecium NRRL B-2354 may be used as a surrogate culture for other nuts and low moisture products. Manufacturers should keep in mind that preventive controls should be validated by a qualified individual such as a process authority.

Validation studies can be performed using the appropriate strains of pathogens or a surrogate culture to validate the log kill rate for each product and piece of equipment. Processes such as oil roasting and blanching can be validated by determining the time/temperature profile in the coldest area of production to demonstrate that the process delivers the desired lethality based on pre-established critical limits. All validation studies should be tested under the worst case scenario, such as lowest temperature, coldest location, maximum throughput, higher product bed depth and fasted belt speed. A process validation report should be written by a process authority on whether or not the nut processing technology consistently achieves the minimal lethality. Adequate Good Manufacturing Practices (GMP) should be in place to prevent processes products from re-contamination.

Are you concerned that your nut-containing product could be carrying a bacterial pathogen? Mérieux NutriSciences offers thermal and non-thermal process validation studies for nuts to ensure food safety. Our process authority services and process validation studies are recognized industry-wide for their attention to detail. Our experts deliver the precise data you need to make informed food safety decisions, providing you with actionable data to verify the effectiveness of your processes and ensure the safety of your finished products. Contact us today to start your process validation study!



Meet the Author

Dr. Erdogan Ceylan
Director of Research, Mérieux NutriSciences

Dr. Ceylan works as Director of Research for Mérieux NutriSciences. He specializes in thermal and non-thermal process validation studies, challenge studies, shelf life studies, detection, identification, and control of foodborne pathogens and spoilage organisms in raw ingredients and finished products. Dr. Ceylan consults with the food industry on FSMA, HACCP, sanitation, microbiological risk assessment, prevention strategies, process control and regulatory requirements. Dr. Ceylan serves as the Responsible Official for the Mérieux NutriSciences select agents and toxins program under the Federal Select Agent Program for Clostridium botulinum research studies. A renowned scientist with nearly 20 years of experience, Dr. Ceylan has given presentations at international meetings including the International Association for Food Protection (IAFP) annual meeting, International Food Technologists (IFT) annual meeting, Reciprocal Meat Conference (RMC), International Dairy Food Association (IDFA) Conference, National Confectioners Association (NCA)/ International Association of Confectioners (PMCA) Quality Management Workshop, North Dakota State University Feed Safety Short Course and Pet Food Forum. He is a member of IAFP and IFT. Dr. Ceylan authors the Yersinia chapter in the Compendium of Methods for the Microbiological Examination of Foods (5th edition) and has published a number of articles in peer-reviewed journals and trade magazines.

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