Assessing postharvest risks for Salmonella in pistachios.

In the past decade, outbreaks associated with consumption of raw almonds and peanut butter have been documented in the U.S. and in 2009 there was a large recall of pistachios when Salmonella was isolated from commercial products. However, with the exception of almonds, very little is known about the ecology of Salmonella in nut production and processing environments impeding the development of targeted commodity-specific intervention programs. Quantitative microbial risk assessment (QMRA) is an increasingly common tool that provides a framework for identifying critical data gaps and evaluating the overall effectiveness of risk-reduction strategies. This proposal will, through laboratory studies, identify points during post-harvest handling of pistachios where Salmonella may be reduced, controlled or amplified. Building upon a previous raw almond QMRA these laboratory data, industry data and expert opinion will be used to construct a pistachio QMRA. The overall goal of this research is to use the laboratory data and QMRA to develop scientifically-based food safety risk-reduction strategies for the pistachio industry.

Nuts and other low-moisture foods have generally been considered low-risks for foodborne illness because they are consumed in a dry state where water activity (available moisture) is too low to support microbial growth. However, it is increasingly recognized that many foodborne pathogens can cause illness at very low concentrations, such that microbial growth is not required. In the past decade, outbreaks associated with consumption of raw almonds and peanut butter have been documented in the U.S. In 2009 there was a large recall of pistachios when Salmonella was isolated from commercial products. With the exception of almonds, very little is known about the ecology of Salmonella in nut production and processing environments impeding the development of targeted commodity-specific intervention programs. Quantitative microbial risk assessment (QMRA) provides a framework for identifying critical data gaps and evaluating the overall effectiveness of risk-reduction strategies. This proposal will, through laboratory studies, identify points during post-harvest handling of pistachios where Salmonella may be reduced, controlled or amplified. Emphasis will be placed on understanding the behavior of inoculated Salmonella during hulling, drying and long-term storage. Building upon a previously generated raw almond QMRA these laboratory data, industry prevalence data and expert opinion will be used to construct a pistachio QMRA. The overall goal of this research is to use the laboratory data and risk model to develop scientifically-based food safety risk-reduction strategies for the pistachio industry.

Our overall objective was to generate data to support development of scientifically‐based risk‐reduction strategies for the pistachio industry. The specific objectives were: 

Objective 1. To identify points during post‐harvest handling of pistachios where Salmonella may be reduced, controlled or amplified. 

Objective 2. To develop a QMRA for Salmonella in pistachios.

The following summarizes the findings of this study. 

1. The results of the QMRA suggest that risk of salmonellosis from consumption of pistachios is very low based on current industry practice and currently‐available data. The risk assessment model can be updated as new data (e.g., prevalence and concentration) become available. However, the current model can be used to support food safety programs for the pistachio industry. 

2. Salmonella will multiply at ambient temperatures and above in in‐hull pistachios, pistachio hulls and pre‐dryer pistachios. Increases in populations of Salmonella are minimal in the first 3 hours but can be significant after 6 h. Holding pre‐dryer pistachios for long periods of time should be avoided when possible. 

3. The float tank is an opportunity for cross contamination of pistachios. Further studies should evaluate means to reduce this potential (e.g., by treating the wash water with antimicrobials that are maintained at an appropriate active level; by applying a rinse after the pistachios leave the float tank). 

4. Microbial populations are reduced in the dryer by approximately 2 to 3 log CFU/g. Most of the reduction occurs in the initial stages of drying. Greater reductions in the dryer may be possible with optimization of the drying times/temperatures. The potential for recontamination after the dryer should be considered.