Prevalence and Amounts of Salmonella Found on Raw California Inshell Pistachios

Abstract

After harvest, pistachios are hulled with mechanical abrasion and then separated in a float tank containing water; the nuts that float (∼15%; floaters) and those that sink (∼85%; sinkers) are dried and stored separately. To determine the prevalence of Salmonella in pistachios, a total of 3,966 samples (1,032 floaters and 2,934 sinkers) were collected within 4 months of the 2010, 2011, and 2012 harvests from storage silos (12 samples from each silo, in most cases) and were stored at 4°C; 100-g subsamples were enriched for the presence of Salmonella. Twenty-one of the floater samples and 11 of the sinker samples were positive for Salmonella: 2.0% prevalence (95% confidence interval [CI], 1.3 to 3.1%) and 0.37% prevalence (95% CI, 0.21 to 0.67%), respectively, for a weighted average prevalence of 0.61%. Levels of Salmonella were determined for positive samples using a most-probable-number (MPN) method with multiple 50-g, three 5.6-g, and three 0.56-g subsamples. Geometric mean levels of Salmonella in floaters and sinkers were 0.66 MPN/100 g (0.14 to 5.3 MPN/100 g) and 0.18 MPN/100 g (0.10 to 0.62 MPN/100 g), respectively. Seven different serovars were identified among the isolates, with nine pulsed-field gel electrophoresis fingerprints; as many as four serovars were isolated from some samples. Salmonella serovars Montevideo (44%), Enteritidis (19%), Senftenberg (16%), Worthington (12%), and Liverpool (9.4%) were most commonly isolated from the initial 100-g samples. The prevalence and levels of Salmonella in pistachios are within those observed for other tree nuts, but the limited number of serovars isolated suggests a narrow and persistent contamination source.

Growth of Salmonella and Other Foodborne Pathogens on Inoculated Inshell Pistachios during Simulated Delays between Hulling and Drying

“…Maximum increases were similar at both high and low inoculum levels, respectively: floaters, early season, 3.33 and 2.94 log CFU/g; floaters, midseason, 2.21 and 1.80 log CFU/g; sinkers, early season, 1.27 and 1.13 log CFU/g; sinkers, midseason, 0.96 and 1.28 log CFU/g. The higher maximum populations of Salmonella in floaters observed in the current study correspond to the higher geometric mean Salmonella levels (0.66 versus 0.18 MPN/100 g for floaters versus sinkers) and wider range (0.14 to 5.3 versus 0.10 to 0.62 MPN/100 g for floaters versus sinkers) previously reported in floater pistachios collected from storage silos (15).…”

“…However, in experiments with paired samples, growth was positively influenced by the presence of higher amounts of hull material. The lack of hull material ( 5%) may account for the significantly lower maximum populations observed on sinker pistachios and could be one reason why, in a previous survey, higher levels of naturally occurring Salmonella were present on dried floaters than on sinkers collected from preprocess silos (15).…”

“…Salmonella and other pathogens cannot grow on dry pistachios but will survive for extended periods under conditions of ambient storage (17). Raw inshell pistachios collected from California storage silos shortly after harvest (2010 through 2012) had a 3-year average prevalence of Salmonella of 2.0% (95% confidence interval [CI], 1.3 to 3.1%; 1,032 samples) for floaters and 0.37% (95% CI, 0.21 to 0.67%; 2,934 samples) for sinkers (15). Geometric mean most-probable-number (MPN) values for Salmonella were higher in floaters (0.66 MPN/100 g; 95% CI, 0.14 to 5.3 MPN/100 g) than in sinkers (0.18 MPN/100 g; 95% CI, 0.10 to 0.62 MPN/100 g).…”

First Complete Genome Sequence of Salmonella enterica subsp. enterica Serovar Worthington Strain CFSAN051295, Isolated from Pistachio

“…Pistachios have been linked to outbreaks of salmonellosis in the United States, with a limited range of Salmonella enterica serovars (Montevideo and Senftenberg), but other serovars, such as Salmonella enterica serovar Worthington, were isolated during a study looking at the prevalence of Salmonella spp. in pistachios ( 2 ). S .…”

Drying and decontamination of raw pistachios with sequential infrared drying, tempering and hot air drying

“…Besides the need to preserve the chemical and sensory quality of pistachios during processing and storage, there is an increasing concern over the microbial safety of pistachio nuts due to the presence of several serotypes of Salmonella enterica in pistachio nuts and pistachio-containing products, which resulted in the recall of more than 16 million pounds of such products by the US Food and Drug Administration in 2009 (CDC, 2009). Surveys of pistachios produced in several countries confirmed the prevalence of S. enterica in pistachios at various levels (Al-Moghazy et al, 2014; Harris and Ferguson, 2013;Harris et al, 2016;Little et al, 2009Little et al, , 2010 and nine recalls of pistachios due to contamination with S. enterica had taken place by July 15, in 2016 in the USA [FDA, 2016). Furthermore, a multistate outbreak of Salmonella Montevideo infections in the USA was linked to in-shell and shelled pistachios grown in California, the world second largest producer and exporter of pistachios after Iran (CDC, 2016).…”