Evaluating Pediococcus acidilactici and Enterococcus faecium NRRL B-2354 as Surrogates for Salmonella enterica on Low Temperature Saturated Steam Pasteurized Cashews and Macadamia Nuts

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2023-02
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Abstract

Low temperature saturated steam pasteurization reduces numbers of Salmonella enterica on macadamia nuts and cashews. Lethality of pasteurization must be verified necessitating identification of non-pathogenic surrogates. Whole cashews and macadamia nuts were co-inoculated with S. enterica and one of three potential surrogates (Enterococcus faecium, Pediococcus acidilactici, and Staphylococcus carnosus) then dried to original water activity (aw) around 0.44 - 0.51. Nuts were packaged in woven polypropylene bags and commercially processed using saturated steam at 85 ± 5°C. Bacteria were enumerated by plating onto TSA with an overlay of XLT-4 for Salmonella, or on media selective for the potential surrogates. Mean reduction (log CFU·g-1) of Salmonella (6.0 ± 0.14) was significantly larger than E. faecium (4.3± 0.12), or P. acidilactici (3.7± 0.14) on cashews. Mean reduction of Salmonella (5.9 ± 0.18) was significantly larger than P. acidilactici (4.4± 0.18) on macadamia nuts, but instances occurred where E. faecium reduction on macadamia nuts exceeded Salmonella. St.carnosus reduction exceeded that of Salmonella and is therefore not an appropriate surrogate. Based on these studies caution should be applied when choosing a surrogate for different types of nuts, as acceptability of E. faecium as a surrogate for Salmonella varied between cashews and macadamia nuts.

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salmonella, food microbiology, food safety
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