Heating Without Harm

Washington State University professor of food engineering and 2024 IFT Fellow Shyam Sablani heads a food packaging and processing research program that seeks to find novel approaches to both.

“We focus on food processing technologies, which include thermals such as microwave and radio frequency,” explains Sablani.

Sablani led two recent projects that used three technologies created as alternatives to conventional thermal treatments for safe, shelf-stable products. Two, microwave-assisted thermal sterilization (MATS) and microwave-assisted pasteurization system (MAPS), were developed by his colleague Juming Tang. The third was pressure-assisted thermal sterilization (PATS).

Some foods need treatments to keep them edible, and while conventional thermal treatments work, they come with a cost. Flavors, colors, nutrients, and textures will degrade, Sablani notes. With a treatment like the microwave-based thermal treatment, the heat is generated from steam or hot water, he explains.

“Because it’s a volumetric process, the entire food heats at the same time rather than going from surface to the center, so your process times are dramatically reduced,” he says. Shorter processing times also mean less quality deterioration, he adds.

The MAPS and MATS technologies were developed over a span of two decades, and Sablani’s team has been testing them with different foods to find out which is most effective. “The next step for us was to see what kind of food products we could pasteurize or sterilize,” he says.

A postdoctoral researcher visiting from Türkiye suggested hummus as a good test product. The team made their hummus with an interesting twist: they used lentils instead of chickpeas. Lentils are a significant crop in the U.S. Northwest, and they’re inexpensive. Once they settled on a lentil hummus recipe, they ran the experiment twice. The MAPS- and MATS-treated samples were stored and tested about every 2 weeks across 4 months. In both cases, the samples were stable and uncontaminated.

And while the researchers didn’t do a full sensory study, they did use their coworkers as taste testers. They offered up their hummus alongside a commercial chickpea-based product as a blind taste test. The lab hummus got high marks; the tasters were surprised when they found it was made from lentils.

“We did this a few times and people really loved it,” says Sablani. “Sometimes they said, ‘Well, we don’t see any difference. Both look great, and both taste great.’”

Healthy Purees

For the other project, the researchers treated vegetable purees with PATS, which combines high pressure and high temperatures.

They chose three vegetables with vibrant colors—red cabbage, carrots, and red beetroot—so they would be able to easily assess color changes throughout the process.

“They have different pigments—anthocyanins, carotene, and so on,” says Sablani. “We can look into the retention of those pigments, which have nutritional value as well.”

The vegetables were pureed and poured into plastic pouches until they were almost full, and the pouches were sealed. Then they were placed into hot water preheated to 98°C for 3 minutes. The samples were sterilized by being put under 600 MPa of pressure at a temperature of 91°C. This process was repeated 21 times. One set of purees was immediately analyzed for quality; the other was stored for 6 months in a warm, dark incubator.

Post-PATS processing, the researchers found that all of the purees’ colors were stable; there was very little change in their richness, even after 6 months.

“From a consumer perspective, all the pigments are very attractive and there’s very little or no degradation of the colors,” Sablani says.

These technologies are, for the most part, still pilot-scale, according to Sablani. He’d like to see food companies adopt these technologies, which, he acknowledges, will probably be a significant investment. But, he says, it’s time for a new approach.ft