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Apr 22 2022

A Booming South African Nut Industry: Avoiding Potential Food Safety Pitfalls 

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Nuts are a nutritious and versatile category of foods and food ingredients. Not only do nuts contain unsaturated fats, they are also a source of essential minerals and phytochemicals. The South African nut industry is the world’s largest producer and exporter of macadamia nuts. It also produces pecans, and on a smaller scale, walnuts, almonds, cashews, hazelnuts, pistachios, and peanuts. Peanuts are the most consumed locally as they are relatively cheap. Domestic and export market demand, particularly for tree nuts, is expected to continue growing(1).
While nut consumption can contribute to a healthy diet, nuts have been identified as a source of Salmonella and E. coli. In addition to outbreaks, nuts have been recalled after isolation of Salmonella (2) or E. coli during routine testing. This has raised awareness of nut products as a potential vehicle for foodborne illness. Although nuts are categorized as low-moisture foods that do not support the growth of foodborne pathogens, research has shown that bacterial cells remain viable for a long time in such foods.

Potential sources of microbial contamination of nuts

There are likely multiple sources of Salmonella and E. coli in nuts, from harvesting to post-harvest processing. One source of microbial contamination is the field or orchard. Mixing the nuts with damp soil and plant debris during harvesting may allow microbial contamination which is then spread to the edible kernels during processing, storage and distribution. The drying process before shelling often reduces microbial counts, but might not kill all of the microbial cells. The remaining populations of Salmonella or E. coli can survive exceptionally well, posing a food safety risk (3). A processing facility contaminated with enteric pathogens may also lead to sporadic re-contamination of the final nut products. Good agricultural and manufacturing practices (GAPs and GMPs) are essential to reduce opportunities for foodborne pathogens to contaminate the crop and finished product.

Common nut processing steps 

Most nuts undergo similar processing steps: drying to prepare for cracking, size separation, shelling, air aspiration to separate shell fragments and impurities, sorting to remove other defects, and a final manual sorting and inspection before packaging. Some types of nuts, such as almond and macadamia, may undergo a deliberate size reduction to produce halves, slivers, or other particle sizes. Processors also use various techniques to further treat nuts including dry roasting, oil roasting, blanching, propylene oxide treatment, steam pasteurization, hot water pasteurization, and combinations of these (4)

Process validation for product safety

To address the risk of manufacturers distributing potentially contaminated nut products, a validated ‘kill step’ should be considered. Process validation studies determine if the treatment/s can effectively control the targeted pathogens and achieve the intended level of food safety. Validation of critical control points is an important part of the HACCP system and global food safety standards such as ISO 22000, FSSC 22000, and BRC.

Validation of a process for one nut type cannot be universally applied to all nuts. Differences in the inactivation of Salmonella or E. coli may exist among nut types due to shape, size, surface area, or other factors impacting treatment. Similarly, process validation should be performed for each type of equipment. For instance, process parameters previously validated using a flatbed roaster might not apply to a rotary roaster, as the two rely on different mechanisms. 

Most validation studies for nut products are conducted in-plant due to challenges in imitating complex processing conditions in a laboratory setting. In such cases, a non-pathogenic surrogate microorganism is used to gather scientific data for the particular process. Enterococcus faecium NRRL B-2354 (ATCC 8459) was found to be a conservative surrogate for Salmonella for the thermal processing of almonds and other nut types. Guidelines published by the Almond Board of California (ABC), National Advisory Committee on Microbiological Criteria for Foods (NACMCF), and ISO/DIS 20976-2 can be used as references for the design of experiments, analysis of results, and documentation of the process validation study.

Mérieux NutriSciences South Africa offers process validation services to the nut industry to ensure safe products for both local and export markets. For each validation project, a comprehensive report is provided. Our validation studies help establish if your processes meet regulatory and global requirements.

References

  1. USDA (2020). Positive outlook for South African tree nut production and trade. https://apps.fas.usda.gov/newgainapi/api/Report/DownloadReportByFileName?fileName=Positive%20Outlook%20for%20South%20African%20Tree%20Nut%20Production%20and%20Trade_Pretoria_South%20Africa%20-%20Republic%20of_06-15-2020 Accessed January 4, 2022.
  2. TimesLIVE (2021). Product recall: Nuts withdrawn after ‘low levels’ of Salmonella detected. https://www.timeslive.co.za/news/consumer-live/2021-12-06-product-recall-nuts-withdrawn-after-low-levels-of-salmonella-detected/ Accessed January 4, 2022. 
  3. Emergency Prevention System Food Safety. (2012). Prevention and control of Salmonella and enterohemorrhagic E. coli in tree nuts. https://www.fao.org/3/au683e/au683e.pdf Accessed January 4, 2022.
  4. Clark, J. P. (2002).  Processing tree nuts. https://www.ift.org/news-and-publications/food-technology-magazine/issues/2002/june/columns/processing Accessed January 4, 2022.  
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