Surrogate for Salmonella on Cashews and Macadamia Nuts Treated with Propylene Oxide

What is it about?

Tree nuts are produced and consumed worldwide, playing a role as a snack or ingredient in foods in several cultures. Traditionally, tree nuts have been believed to be microbiologically safe due to their composition and lack of water available to harbor pathogenic bacterial growth. However, recent years have proven to be problematic for many tree nuts and nut products, numerous recalls have occurred in the United States for verified contamination of Salmonella. Since Salmonella can be found in food systems worldwide, and is a leading cause of foodborne illness due to bacterial contamination of food, steps must be taken to improve the safety of nuts grown locally and imported products. With several processing options for tree nuts, two that are commonly practiced to reduce microorganisms include a fumigation of product using propylene oxide (PPO) and a thermal inactivation treatment through use of saturated steam. The comparison of Salmonella inactivation and non-pathogenic surrogate bacteria on cashews and macadamia nuts, being processed in these two manners, was investigated. Possible bacteria strains that were investigated for surrogacy were Enterococcus faecium NRRL B2354 (ATCC #8459), Pediococcus acidilactici (ATCC #8042), and Staphylococcus carnosus (ATCC #51365). Surrogates are bacteria that have similar inactivation characteristics as Salmonella when processed, that can be purposely introduced before processing to ensure inactivation of Salmonella and is harmless if consumption occurs. Studies continue to ensure safety of tree nuts as well as complying with pending and future regulations.

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Why is it important?

A non-pathogenic bacteria is identified that has similar inactivation to a human pathogen, Salmonella. This surrogate bacteria can be used within nut processing facilities to verify the effectiveness of PPO fumigation to reduce human pathogens.