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Photo: ARS engineer Zhongli Pan examines a pan of almonds.
ARS engineer Zhongli Pan is part of a team that has developed a chemical-free process to reduce Salmonella contamination of almonds.

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Infrared-Based Approach Explored for Keeping Almonds Safe to Eat

By Marcia Wood
February 21, 2012

Giving almonds a burst of infrared heat, followed by a stint of hot-air roasting, helps make sure these tasty, healthful nuts remain safe to eat. That's according to studies by U.S. Department of Agriculture (USDA) engineer Zhongli Pan and microbiologist Maria T. Brandl, who have dubbed this almond pasteurizing technique "SIRHA," short for "sequential infrared and hot air."

Findings from their laboratory experiments show that this chemical-free process offers a simple, safe, energy-efficient and environmentally friendly way to reduce Salmonella enterica populations to levels generally recognized as safe.

Pan and Brandl are with the USDA Agricultural Research Service (ARS) Western Regional Research Center in Albany, Calif. ARS is USDA's chief intramural scientific research agency. The almond research is one example of ARS studies that enhance food safety, a USDA priority.

All almonds processed for sale in the United States today are treated with some kind of pasteurization process in order to zap Salmonella, even though it's generally thought that almonds are only rarely contaminated with this pathogen.

Nearly a half-dozen almond pasteurization methods already have federal approval, but many almond processors remain eager to learn about new options, including SIRHA and its promise of fast, reliable and relatively economical pasteurization

According to results from dozens of volunteer taste-testers who participated in the studies, infrared heating doesn't detectably alter the mild taste, smooth texture, attractive appearance or other characteristics that make almonds one of the country's most popular tree nuts.

With further work, SIRHA should be easy to scale up for use at packinghouses, Pan reports. Most are located in California, where all of America's commercial almonds—80 percent of the world's supply—are grown.

Some almond packinghouses already use infrared heating, but not for pasteurizing, Pan notes.

The idea of using infrared heating to kill germs isn't new. But studies that Pan and Brandl reported in peer-reviewed articles in the Journal of Food Engineering in 2010 and 2011 and in the Journal of Food Protection in 2008 are likely the most comprehensive investigations of the use of infrared heating to pasteurize almonds and knock down Salmonella.

Pan and Brandl collaborated in these studies with ARS research leader and food technologist Tara H. McHugh, food technologists Gokhan Bingol and Donald A. Olson, and technician Steven Huynh, all at Albany; former University of California-Davis graduate students Jihong Yang and Yi Zhu; and Hua Wang, a professor at Northwest Agricultural and Forestry University, Yangling, Shaanxi, China.

Read more about this research in the February 2012 issue of Agricultural Research magazine.