Using Intense Pulsed Light Technology to Decontaminate Dry or Powdered Food

March 1, 2018

male researcher pours a bag of powdered food into a metal feeder that's part of a non-thermal pasteurization machine using intense pulsed light.Ph.D. student Dongjie Chen pours powdered food into the volumetric feeder of the intense pulsed light-based non-thermal pasteurization system.

The next advancement in intense pulsed light (IPL) technology may be coming in the form of non-thermal pasteurization.

Roger Ruan, a professor in the Department of Bioproducts and Biosystems Engineering at the University of Minnesota, is leading a research project using IPL technology to reduce harmful bacteria and other microorganisms in dry or powdered foods. He’s testing non-fat powdered milk, wheat flour, black pepper, and egg white and whole egg powders.

Ruan’s experimental IPL non-thermal pasteurization system was able to reduce bacteria by 99.9% to 99.99999%, depending on the type of dry or powdered food tested.

“Detection of foodborne pathogens in dry and powdered food has been increasing in the United States causing major recalls and is currently of major concern to the food industries and consumers,” Ruan said.

Bacteria and other microorganisms usually do not grow as well in dry or powdered food compared with food with more moisture. But, they can still be present for long periods of time. If they are present in high enough numbers, they may cause foodborne outbreaks.

“Dry or powdered foods are usually pasteurized in the liquid state,” Ruan said. For example, milk is pasteurized at 161.6 degrees Fahrenheit for 15 seconds before it’s evaporated for milk powder products.

A bacteria that can thrive in dry or powdered food is Cronobacter. It’s been found in powdered infant formula, powdered milk, herbal teas, and other dry foods. Though foodborne illnesses caused by Cronobacter are rare, they’re “frequently lethal for infants,” according to the Centers for Disease Control and Prevention.

Cronobacter has a tolerance for high temperatures, making conventional pasteurization processes insufficient. Ruan’s IPL treatment system may solve this problem.

How it works

intense pulsed light-based non-thermal pasteurization system by roger ruanProfessor Roger Ruan and his team are testing an intense pulsed light-based non-thermal pasteurization system for dry and powdered food. Upon completion of the project in 2019, a prototype will be built and demonstrated.

The dry or powdered food gets inoculated with one of two kinds of bacteria: Cronobacter sakazakii or Enterococcus faecium, a nonpathogenic surrogate for Salmonella. Ruan and his team also plan on testing foods with Bacillus cereus, a bacteria that causes food poisoning.

The food is analyzed for bacteria, and then it gets placed into a volumetric feeder, which goes down a tube and onto a stainless steel vibratory feeder. The food tumbles gently through the vibratory feeder as it gets exposed to the IPL. This is where decontamination happens.

The IPL treatment system kills bacteria in three ways:

  • Photochemical effect: The ultraviolet light portion of the pulsed light damages the DNA of bacteria.
  • Photothermal effect: Localized heating of bacteria is induced by the pulsed light due to the difference in the heating and cooling rate, absorption characteristics of the bacteria, and the dry or powdered food. Thus, the bacterial cell acts as a local vaporization center that may lead to membrane destruction and cell wall rupture. Thermal stress also lead to rupture of microbial cells, especially at higher flux densities.
  • Photophysical effect: Pulsed light is expected to induce some physical disruption on microbial cellular structures caused by the intermittent, high-intensity pulses. Researchers observed cell wall damage, membrane rupture, cytoplasm damage, etc. in bacterial cells exposed to pulsed light, suggesting that photophysical effects can play a vital role in microbial inactivation.

After exposure to IPL, the food exits the feeder, and it gets collected onto a tray where it will be analyzed again.

“The process takes about 30 seconds, depending on the kind of dry or powdered food,” said Dongjie Chen, a Ph.D. student responsible for the setup and operation of the IPL system as well as the design of the experiments.

Ruan and his team are also examining the effects of IPL treatment on the physical, chemical, nutritional, and sensory properties of the foods. Those results are not yet available. Upon completion of the project in 2019, a prototype IPL system will be built and demonstrated.

Optimistic outlook

IPL-based technology for non-thermal pasteurization does not yet exist in the food industry, but Ruan hopes to change that.

“The successful development of the proposed IPL technology would enable the food industry to use a non-thermal process to disinfect food products while maintaining its nutritional and sensory quality,” Ruan said. “This would provide consumers safe and acceptable food products with confidence.”

For more information about the project, please contact Ruan,


The project is a collaborative effort among university researchers in food engineering, microbiology, chemistry, sensory evaluation, and extension; food industry partners; and non-profit organizations. Co-principal investigators include David Baumler, Chi Chen, Paul Chen, Zata Vickers, Joellen Feirtag, and Laurence Lee. The current system was developed by Peng Peng, Nan Zhou, Dongjie Chen, and Yanling Cheng. The new system under development is mainly done by Erik Anderson, Peng Peng, Yanling Cheng, Dongjie Chen, and Juer Liu. Most of the experiments and analysis are done by Dongjie Chen, Juer Liu, Justin Wiertzema, Qingqing Mao, and Yiwei Ma.

This is a Coordinated Agricultural Project funded by the Agriculture and Food Research Initiative from the U.S. Department of Agriculture National Institute of Food and Agriculture.