Atmospheric Cold Plasma Offers Flour Treatment Benefits

Wheat flour is chlorinated to give it the functionality that is prized for products like high-ratio cakes that are light, fluffy yet firm, and good at absorbing sugar. Chlorination also whitens flour.

Chlorination is a process that uses chlorine gas, but there are problems with this method. It’s a health hazard for workers who are exposed to it, and it’s not clean label. Chlorination is banned in the European Union and several other countries, including China.

“There are two primary reasons that are driving the move away from chlorination,” says Jayne Bock, technical director at the Wheat Marketing Center in Portland, Ore., and an adjunct professor at Oregon State University’s College of Agricultural Sciences. “One would really be personnel safety at the facilities where the chlorination is being applied. The second reason is with this movement toward more clean label products, chlorination does not translate well to clean label, and so there’s not a lot of consumer support for that type of processing technology being applied to cake flours.”

In a recent project, Texas A&M University researcher Janie McClurkin Moore, an assistant professor with the Department of Biological and Agricultural Engineering, teamed with Bock and Shikhadri Mahanta, a Texas A&M graduate student in biological and agricultural engineering, to use atmospheric cold plasma (ACP) as an alternative to flour chlorination. They found that ACP has none of the safety risks but provides comparable functionality.

“Our research has demonstrated that ACP can achieve similar or superior enhancement in flour quality—such as improved dough strength and elasticity—without the need for harmful additives,” says Mahanta, who will graduate with a PhD this summer.

Testing ACP Treatments

Moore compares ACP to using the energy of lightning to sanitize food. Lightning is a plasma, she explains, and the cold plasma created during ACP treatments is a specific type of air that produces reactive gases. Those gases interact with microbes on a food and so sanitize it. ACP treatments also change the structures of a food product’s protein and starches.

Mahanta led two projects that used ACP treatments on different flours. While there’s been previous research on using ACP to treat flour, she says there are no standards that describe best practices. This is important because too much ACP can damage a flour’s protein structure, and that causes problems with functionality, like the inability of the flour to hold water.

The first research project focused on high-ratio cakes, which have a high sugar-to-flour ratio and are a significant part of the cake market. The researchers used untreated wheat flour samples of 100 grams each. Those were treated with ACP at different voltages—50 kilovolts, 60 kilovolts, and 70 kilovolts. Each was treated for 5, 6, and 7 minutes. Next, samples of untreated, chlorinated, and ACP-treated flour were analyzed for color, moisture, protein, pasting properties, and pH.

They then made 11 cakes using all the flours, the nine ACP-treated samples, the chlorinated, and the untreated. The cakes were baked at 375°F for 23 minutes in a reel oven and were evaluated for volume, texture, and cell structure.

What they found is that there’s a sweet spot for ACP treatment—not too much and not too little. The samples treated at 60 kilovolts for 5 or 6 minutes gave the best overall results. “Moderate ACP treatments are most effective,” says Mahanta.

Mahanta’s follow-up study researched soft and hard wheat to make bread. Soft wheat has less protein than hard, which is important because ACP mostly impacts wheat’s protein content, she explains. “We wanted to see the effects in the end products,” she says. “Do we get any improvement in the existing breads if we use ACP-treated flour?”

For that study, they treated hard wheat flour as they did the soft flour in the cake study, at 50 kilovolts, 60 kilovolts, and 70 kilovolts timed at 5, 6, and 7 minutes. They then made 10 loaves of bread. (They didn’t use a chlorinated flour in this study.)

And, like in the cake study, they found that higher rates of ACP treatment didn’t provide the best results, Mahanta says. ACP treatment at 70 kilovolts for 5 minutes resulted in better dough strength. High levels of treatment, however, produced dough that was too stiff. The flour treated with ACP at 60 kilovolts for 5 and 6 minutes gave the best volume and texture.

You have the desired functionality that basically is the same as chlorination, but you’ve removed the safety hazards.

Jayne Bock

Wheat Marketing Center and Oregon State University

Setting ACP Standards

Because there isn’t a guideline for ACP treatment, Mahanta says she would like to create a model for others to use. “It would be beneficial for the industry and also for future researchers to find the exact changes in the properties of the wheat flour when we have a specific number to treat that wheat flour.”

There are other methods for treating flour, the most popular being thermal treatment. But Mahanta says the end product isn’t as good as flour that has been chlorinated. The ACP research results demonstrate that ACP is a valid treatment for flours that could replace chlorination in the food industry.

“The results that we have started to see are that with this process and this treatment, we can engineer the system and engineer the process in order to achieve the same results or better results than what we see from the industry and their chemical treatment,” says Moore.

Although this research is still in its early stages, the researchers think that adding ACP to an existing processing line shouldn’t be too difficult or expensive. They estimate an initial cost of $15,000; the system’s energy consumption is equivalent to that of a microwave.

“My assumption is that as research continues and the technology develops and scales up, that it would be some sort of in-line type of treatment that shouldn’t be overly challenging to integrate into a commercial flour mill producing cake flour,” says Bock.

But once ACP treatments reach commercial scale and—just as importantly—are accepted by consumers as safe, the potential market is large, according to Bock.

“You have the desired functionality that basically is the same as chlorination, but you’ve removed the safety hazards and you’ve also removed the non-clean label perception that comes along with chlorination,” Bock says.

ACP also affords important sustainability benefits for grains, explains Mahanta, who is passionate about addressing food waste. “ACP treatment has been shown to stimulate seed germination and reduce the uptake of toxic heavy metals like cadmium in grains, contributing to safer agricultural inputs and reducing food loss associated with contaminated or non-viable seed lots,” she says.

“Overall, our work demonstrates that cold plasma is a sustainable and scalable technology that addresses food loss and waste across multiple points in the cereal grain value chain—from storage to processing to crop production,”ft