Saturated steam (SS) and propylene oxide (PPO) fumigation are two common methods to improve microbiological quality and safety of tree nuts. Validation of these processes is needed to ensure adequate control of bacterial pathogens. Since pathogens cannot be studied in food processing environments, surrogates with resistance comparable to the pathogens needed to be identified. The objective was to investigate the suitability of Enterococcus faecium, Pediococcus acidilactici, and Staphylococcus carnosus as surrogate bacteria for Salmonella spp. on whole cashews and macadamia nuts, processed with SS or PPO.
Whole cashews and macadamia nuts were co-inoculated with a cocktail of Salmonella enterica and one of the three potential surrogates. Nuts were dried to original aw, packaged in poly-woven bags (2.3 kg) and commercially processed using vacuum assisted steam at 80 ͦ C or PPO fumigation. Salmonella and the potential surrogates were enumerated by serial dilution, and plated onto TSA with overlay of XLT-4 (Salmonella) or media selective for the potential surrogates.
Mean log reductions (CFU/g) of Salmonella and each potential surrogate were compared using a paired T-test. SS results: reduction of Salmonella (6.0 ± 0.14) was significantly larger than E. faecium (4.3± 0.12), or P. acidilactici (3.7± 0.14) on whole cashews. Salmonella (5.9 ± 0.18) was significantly larger than P. acidilactici (4.4± 0.18) on whole macadamia nuts.
PPO results: reduction of Salmonella (7.3 ± 0.19) was significantly greater than E. faecium (6.4± 0.31), or P. acidilactici (6.3± 0.33) on whole macadamia nuts. Reduction of Salmonella was significantly greater than E. faecium and P. acidilactici reduction on cashews.
P. acidilactici may be considered a surrogate for Salmonella reduction on whole macadamia nuts and whole cashews processed using SS at 80 ͦ C. E. faecium and P. acidilactici may be considered surrogates for Salmonella reduction on whole macadamia nuts and whole cashews processed using PPO. Reduction of St. carnosus exceeded that of Salmonella indicating it is not a suitable surrogate for Salmonella using either processing intervention. / Master of Science in Life Sciences / 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 <i>Salmonella</i>. Since <i>Salmonella</i> 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 <i>Salmonella</i> 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 <i>Enterococcus faecium</i> NRRL B2354 (ATCC #8459), <i>Pediococcus acidilactici</i> (ATCC #8042), and <i>Staphylococcus carnosus</i> (ATCC #51365). Surrogates are bacteria that have similar inactivation characteristics to <i>Salmonella</i> when processed, that can be purposely introduced before processing to ensure inactivation of <i>Salmonella</i> and is harmless if consumption occurs. Studies continue to ensure safety of tree nuts as well as complying with pending and future regulations.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/86138 |
| Date | 30 May 2017 |
| Creators | Saunders, Thomas Philip |
| Contributors | Food Science and Technology, Ponder, Monica A., Huang, Haibo, Williams, Robert C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
Page generated in 0.0024 seconds