Infrared heat: A new wavelength for food security

Food poisoning from salmonella is hard to trace and harder to prevent. The U.S. Centers for Disease Control and Protection says Salmonella Saintpaul is the strain responsible for 1,330 cases identified in 43 states and Canada since April 2008.

This latest mass outbreak has just been linked, through genetic analysis, to some hot peppers from Mexico.

Clearly, salmonella gets around. So how do you prevent pathogens and other mobile pests like moths and weevils from contaminating the food supply in the first place?

Infrared heat is one technology that can kill salmonella on almonds. It has also proven effective in disinfesting crops like rice from insects, their eggs and larvae.

Virgil Macaluso, president of Kansas-based Catalytic Drying Technologies, which manufactures infrared heat systems, says the lessons learned on the auto assembly line led them to new applications for the food industry.

"When the paint chemistry changed to water-based coatings to comply with environmental mandates, we found we could dry water-based paints quicker," says Macaluso. "The infrared wavelength has an affinity for water."

This is important for killing insects because adult insects, their larvae and eggs have a high water content. The infrared radiant energy targets this water. Since insects are higher in moisture than the grain, flour or dry products hosting the infestation, the energy is absorbed rapidly by the organisms they heat up and die in seconds when exposed to infrared energy.

"Companies can use a sieve to get the dead insects out," says Macaluso.

Feeling the heat

Infrared radiation is energy that we feel as heat. It is in the spectrum just below the energy that can be seen with the naked eye, but is a higher-frequency wavelength than microwaves.

The term infrared is from the Latin root infra, or below.

"All substances have a peak of what they absorb whether they are glass, wood or metal," says Mancuso. "Water has three peaks and it likes to absorb infrared heat the most."

The Catalytic Drying system uses natural gas or propane. Macaluso says when gas comes in contact with their platinum catalyst, it creates a chemical reaction known as oxidation reduction. Macaluso says that in effect, the platinum catalyst acts as an after-burner just like a catalytic converter in a car helps burn exhaust to reduce hydrocarbon emissions out the tail pipe. The gases produced include small amounts of carbon dioxide and water vapour.

Tara McHugh is research leader in the Processed Food Research unit at the United States Department of Agriculture (USDA)). She and colleague Zhongli Pan are experts in the use of infrared heat, and food quality and safety.

"We are partnering with companies to explore the potential to improve food safety," says McHugh. "We are looking at almonds infected with salmonella and the research is very promising."

Macaluso says the company is working on an industrial-sized infrared system for the U.S. Department of Agriculture (USDA) in California. The USDA's Western Research Regional Center outside Berkeley specializes in food quality and safety, and in May 2008, it published in the Journal of Food Protection a peer-reviewed article about reducing salmonella in almonds with infrared heat.

The centre's research was fast-tracked by the 2004 salmonella scare when 25 cases of the disease were linked to eating raw almonds and 13 million pounds (about 5,898 tonnes) were recalled from Costco and other retailers. Almonds are a $3-billion US industry in California, and the state provides 80 per cent of the global supply.

The USDA treated raw almond kernels with infrared heat under various conditions of time and temperature. Their results demonstrated that short time exposures of kernels to infrared heat (7.5-log10 kill) killed Salmonella Enteritidis on kernels inoculated in the laboratory. A log (logarithm) reduction refers to how much bacterial contamination can be reduced during a process such as pasteurizing with heat or chemicals. In 2006, the California Almond Board established a minimum 4-log reduction for consumer protection.

In addition to their salmonella research McHugh says the USDA lab has used infrared heat to dry and dehydrate a variety of fruits, including bananas, apples, blueberries and strawberries. "We think the final product is of better quality than freeze-dried," she says.

The USDA thinks cheaper operating costs will drive a wider acceptance of infrared drying systems.

"A lot of our work is to lower the costs to eat fruits and vegetables," says McHugh. "If you can show in your research that there are clear energy savings that is a very important point." Infrared heat dehydrates and dries products much faster than freeze-drying, blanching and convection the most common food-processing technologies.

Farmer prefers infrared over convection

One Canadian customer who agrees is John Wenninger, a sweet potato farmer from Aylmer, Ont. He is drying sweet potatoes to make gluten-free flour for the neutraceutical market. He tried convection but did not like the results. A lab technician recommended he look into infrared heat instead.

Wenninger imported an infrared system and has dehydrated a range of produce and grains.

"We do a bunch of testing for products like pumpkin and orange peel for a brewery," says Wenninger. "We've done mushrooms, garlic, asparagus, and we've tried berries. We find root crops and vegetables work very well in the system."

Each product has an optimal drying time and temperature on the conveyor based on its moisture content. For Wenninger, it is a process of trial and error to find that mix.

He says cost savings are possible because the infrared system is fast and efficient in what it targets to heat. Infrared heat penetrates the product to release moisture and does not waste fuel by heating the air.

"We cube our products to five millimetres and run it on the conveyor under the infrared heat," says Wenninger. "Infrared is an interesting system because the reflective heat off the product is very high from 180 to 200 degrees Fahrenheit. But the product temperature itself, it's in 140 the 150 zone, which is what we want to retain nutrients."

McHugh is confident that innovators like Wenninger who are working with small batches of product will help make the technology mainstream more quickly.

"We have good luck working with small companies," says McHugh. "They can result in big breakthroughs."

And with persistent pathogens like salmonella disrupting food safety, the infrared wavelength could heat up the market.