ORLANDO, Fla. - New research is showing how growers and handlers of almonds and other nuts can use heat treatment in the drying process to kill salmonella.

Nut study finds heat can kill salmonellaA series of salmonella outbreaks in almonds beginning in 2001 prompted California's almond industry to develop industry food safety protocols.

The study, conducted by Linda Harris, a University of California-Davis, cooperative extension microbial food safety specialist, was presented at the Davis-based Center for Produce Safety's June 28 Produce Research Symposium in Orlando, Fla.

Harris started a process to reduce Salmonella Enteritidis phage type (PT) 30, a rare salmonella type, and its cousin, type 9C, to protect the almond industry from outbreaks similar to the 2001 and 2004 U.S. recalls and a 2006 Swedish recall.

To broaden application to other parts of the nut industry, Harris enlisted the assistance of a University of Florida, Gainesville, researcher to examine how pistachios, pecans and peanuts react to salmonella.

The research, conducted October 2009 to September 2010, studied the best moisture levels to store almonds and how moisture affects heat resistance.

Harris, who has a collection of 150 salmonella organisms, inoculated almonds, dried them and exposed them to hot oil in the oil roasting process. Almonds typically possess less than 7% moisture, and her research showed that moisture affects the amount of salmonella reduction. That reduction, however, occurs at different moisture levels of 4% and 6%. That's a difference in initial reduction when the almonds receive a moist heat effect or burst of steam that can kill organisms, she said.

"A range of desiccation tolerance is seen among salmonella strains," Harris said. "But survival after desiccation storage is similar. These data confirm the appropriateness of having used type 30 to do the evaluation studies, and overall, we will use this data to help the industry fine-tune some of its validation guidelines."

Harris said the data should help the overall produce industry because it showed - through five years of study of an almond orchard infected with the type 30 organism - that scientists could pull salmonella out of the environment. That orchard, where salmonella environmentally persists, could be part of the key for desiccation tolerance, she said.

Tim Birmingham, director of quality assurance and industry services for the Almond Board of California, Modesto, said the research helped fill some industry knowledge voids.

"We have been marching down this road for years," Birmingham said. "We did a lot of work early on so we could develop validation protocols, inoculation protocols and procedures. We wanted to give guidance to the industry on specific protocols they could follow. We were going back, dotting our I's and crossing our T's."

In another project funded by the research center, Harris is studying postharvest risks of salmonella in pistachios.

Scheduled for completion in September, that study should provide scientific foundation for a hazard assessment of postharvest pistachio handling, she said. Results show that harvest to hulling time significantly influences microbial growth, drying reduces microbial levels, and the potential for cross contamination exists in float tanks.

Additionally, the research shows that salmonella does not grow on dried pistachios even at relatively high moisture levels.

The Packer will report on more Center for Produce Safety research projects in coming weeks.

Information on the center's research is on its website.