Survey of Salmonella in raw tree nuts at retail in the United States

Abstract

The objective of this survey was to estimate the prevalence, contamination level, and genetic diversity of Salmonella in selected raw, shelled tree nuts (Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios, and walnuts) at retail markets in the United States. A total of 3,374 samples of eight tree nuts were collected from different types of retail stores and markets nationwide between September 2015 and March 2017. These samples (375 g) were analyzed using a modified FDA's BAM Salmonella culture method. Of the 3,374 samples, 15 (0.44%) (95% confidence interval [CI] [0.25, 0.73]) were culturally confirmed as containing Salmonella ; 17 isolates were obtained. Among these isolates, there were 11 serotypes. Salmonella was not detected in Brazil nuts (296), hazelnuts (487), pecans (510), pine nuts (500), and walnuts (498). Salmonella prevalence estimates in cashews (510), macadamia (278), and pistachios (295) were 0.20% (95% CI [<0.01, 1.09]), 2.52% (95% CI [1.02, 5.12]), and 2.37% (95% CI [0.96, 4.83]), respectively. The rates of Salmonella isolation from major/big‐chain supermarkets (1381), small‐chain supermarkets (328), discount/variety/drug stores (1329), and online (336) were 0.29% (95% CI [0.08, 0.74]), 0.30% (95% CI [0.01, 1.69]), 0.45% (95% CI [0.17, 0.98]), and 1.19% (95% CI [0.33, 3.02]), respectively. Salmonella prevalence in organic (530) and conventional (2,844) nuts was not different statistically ( P = 0.0601). Of the enumerated samples (15), 80% had Salmonella levels ≤0.0092 most probable number (MPN)/g. The highest contamination level observed was 0.75 MPN/g. The prevalence and contamination levels of Salmonella in the tree nuts analyzed were generally comparable to previous reports. Pulsed‐field gel electrophoresis, serotype, and sequencing data all demonstrated that Salmonella population in nuts is very diverse genetically. Practical Application The prevalence, contamination level, and genetic diversity of Salmonella in eight types of tree nuts (3,374 samples collected nationwide) revealed in this survey could help the development of mitigation strategies to reduce public health risks associated with consumption of these nuts.

U.S. Consumers’ Tree Nut Food Safety Knowledge, Perceptions, and Handling Practices across Demographic Groups

“…Although Salmonella cannot grow in lowmoisture foods, it is known to survive for a long period of time [9]. Previous research has isolated foodborne pathogens, primarily Salmonella, from 0.35 to 4.20% of 375 g U.S. retail samples of raw cashews, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios, and walnuts [12,13]. Only 69% of the survey participants recognized that tree nuts can be contaminated during harvest and processing events.…”

“…Thus, consumers may not know whether the tree nuts they purchased have been treated to reduce foodborne pathogens. Foodborne pathogens, primarily Salmonella, have been isolated from raw tree nuts purchased at retail stores [12,13], and many consumers source their tree nuts from retail channels [24,35].…”

“…Tree nuts can be contaminated at multiple points from harvest to consumption. Previous studies isolated Salmonella from raw cashews, macadamia nuts, hazelnuts, pine nuts, pecans, walnuts, and pistachios sold for retail in the U.S. [12,13]. Raw tree nuts were associated with multiple outbreaks and recalls, including products made from them [14].…”

Lipid Oxidation and Volatile Compounds of Almonds as Affected by Gaseous Chlorine Dioxide Treatment to Reduce Salmonella Populations

“…have occasionally been detected in almonds and almond products. 13 Salmonella spp. have the ability to survive in low water activity environments and represent a major food safety concern in almonds and other low moisture commodities.…”

“…More recently, Salmonella spp. have occasionally been detected in almonds and almond products Salmonella spp.…”