UC Davis

Between 2013 and 2021, six outbreaks of salmonellosis were associated with consumption of cashews and cashew cheese analogs, yet little is understood about the behavior of Salmonella in cashews or products made from them. The prevalence, levels, and types of Salmonella that may be associated with raw cashew kernels are largely unknown and growth of Salmonella has not been assessed during the fermentation of cashew cheese analogs. The nut-based dairy analog market is growing rapidly, and understanding the safety of nut-based products is crucial as consumers purchase and prepare fermented cheese analogs with increasing regularity. In this thesis, the levels and distribution of Salmonella were determined in naturally contaminated cashew pieces used to prepare a cashew Brie analog associated with a 2020–2021 salmonellosis outbreak. Two unopened boxes from a single lot of cashew kernel pieces were each divided into seven approximately equal units and 10 50-g subsamples per unit were enriched for the presence of Salmonella. Salmonella was uniformly distributed throughout the boxes. Salmonella levels were 0.0023 MPN/g (95% confidence interval [0.0014, 0.0038]) using most probable number (MPN) estimations. Four Salmonella serovars were isolated from the cashew pieces: Salmonella Fresno, Salmonella Nima, Salmonella Urbana, and Salmonella Vinohrady. Two of these serovars, Salmonella Urbana and Salmonella Vinohrady, were in common with the outbreak-associated serovars linked to the 2020–2021 salmonellosis outbreak. Salmonella Fresno and Salmonella Nima were unique to the present study. Following the recipe used by the implicated 2020–2021 cashew Brie analog producer, a fermented cashew cheese analog was prepared and Salmonella behavior was assessed. Salmonella-inoculated cashews were soaked under refrigeration for 24 h, then drained and blended to achieve a smooth paste. A commercial Lactococcus lactis starter culture and, in some cases, 1 or 2% NaCl or 0.5% citric acid were added to the cashew paste which was then held at ambient temperature for up to 72 h. Total aerobic bacteria counts, pH, and Salmonella levels were measured throughout the fermentation. Total aerobic bacteria (measured on M17 agar held at 30°C for 48 h) reached maximum levels of 9–9.5 log CFU/g after 48 h regardless of the presence of Salmonella or starter culture. The starting pH for the cashew cheese analog was 6.0, with final pH between 4.5 and 5.0 by 72 h, regardless of the presence of starter culture. Salmonella levels increased significantly (P ≤ 0.05) by 5.5–7.0 log when no starter culture was added to Salmonella-inoculated cashews. With starter culture, Salmonella levels increased significantly by 0.50–1.5 log; similar increases were observed when 1% or 2% NaCl was included. No significant change in Salmonella levels was observed with the addition of 0.5% citric acid. The findings from this work suggest that addition of starter culture and citric acid significantly inhibit the growth of Salmonella during cashew fermentation but additional control measures that exclude or reduce pathogens may be needed when preparing fermented cashew cheese analogs.