Success in significantly reducing the presence of harmful microbes in flour has been achieved on a limited scale but cost, impact on flour functionality and consumer acceptance are major factors limiting microbe reduction on a broader scale, said Debi Rogers, Ph.D., director of baking services at AIB International in Manhattan, Kansas, U.S. The latter — consumer acceptance — may be a major hurdle for new microbial treatments now in the testing phase, she said.

Heat treatment currently is the most widespread method of microbial reduction in flour. It involves a combination of temperature, time and water activity. Some treatment may be referred to as pasteurization, which also utilizes heat. A major drawback of the heat treatment method of microbial reduction is its effect on the baking qualities of flour.

There are other methods of treatment under review that do not negatively affect the baking qualities of flour, specifically on gluten, including electron beam and cold plasma, both of which face major obstacles in scaling up to commercial levels. Irradiation also is a possible treatment method that has been approved by the U.S. Food and Drug Administration for pest control in flour and for other purposes, but the much higher levels of irradiation needed for microbial reduction in flour have not been approved.

Because heat treatment of flour affects key bread making qualities, most all-purpose or bread-baking flours milled from hard wheats are not treated. Flour from soft wheat used in cake mixes, cookies, breadings, soups and similar applications is more likely to be heat treated because the process does not have a significant effect on qualities important to those applications.

Contamination in flour is rare because it has a low moisture content that is not conducive to microbial growth. Flour typically has a water activity below 0.85aw, with activity of 0.95aw or above needed for bacterial pathogen growth. Low water activity only inhibits microbial growth. It doesn’t kill microbes already present, which can remain present in flour all the way to the end user.

Expense certainly is a factor in decisions about whether to treat for microbial content since the process significantly adds to the final cost of the product. Since most flour goes through a “kill” process before final consumption, such as baking bread and pastries, frying coatings or toasting ready-to-eat cereals, it is hard to justify the cost treatment in most cases. As a result, microbial content of flour typically has not been an issue because it is considered an ingredient, not a food product that is directly consumed in its raw form.

But that doesn’t mean microbial contamination hasn’t been an issue as flour has many opportunities to become contaminated from the farm to the end user. A recall of flour by General Mills in May 2016 that was expanded in June 2016 was due to E. coli. Another recall of Smucker Foods of Canada’s Robin Hood flour in Canada occurred in March of this year related to cases that occurred from November 2016 to late February 2017. Food scientists suggest the microbial contamination reflected in those two incidents isn’t necessarily new to flour, but better detection from improved instrumentation and testing methods may be uncovering what already was there.

While increased testing will be necessary under new FSMA rules, sample testing isn’t foolproof because it sometimes misses a concentrated area of microbial presence since microbes are not necessarily distributed evenly throughout the product, especially in the case of large commercial loads.

“Sampling does not tell you it’s safe,” said Theodore Labuza, Ph.D., Morse Alumni Distinguished Professor of Food Science and Engineering at the University of Minnesota, who is pioneering the use of cold plasma as a microbial treatment for flour.

Further, any current or potential treatment method does not eliminate the presence of harmful microbes in flour. The goal is to reduce their presence to levels that are deemed safe by government regulation or accepted manufacturing practices.

Finally, as more aspects of FSMA go into effect, the industry must refocus on prevention of, rather than reaction to, food-borne illness outbreaks, which raises the bar for food manufacturers. It should be noted that most food manufacturers, including the flour milling industry, already have safety and hygiene measures in place as part of good manufacturing practices to meet government regulations, but FSMA will require validation that methods used for microbial reduction actually achieve the results that are claimed.

To that end, AIB International has developed several product specific Baking Process Kill Step Calculators that allow commercial bakers “to evaluate the lethality of a thermal process (baking) to destroy Salmonella in their products and demonstrate the effectiveness of the process to comply with FSMA’s preventative controls rule.” The calculators work by using time and product temperature parameters to automatically determine total process lethality, reported as an x-log reduction for Salmonella, the greatest problem in low-moisture products such as flour.

Most treatment processes for microbial reduction aren’t new to the food industry, although they may be new to flour millers since treatment of flour is rare. In some cases, technology has been used in other sectors of food manufacturing, especially meat, poultry, produce or other areas that are more susceptible to microbial contamination. But as detection grows more specific, and FSMA comes more into play, even industries that typically have not had issues, such as flour milling, now must consider measures to improve food safety.

General Mills, for instance, the focus of the 2016 flour recall, said recently it increased its spending on food safety to $16 million in 2016 from $13 million in 2015. 

Current ‘ready-to-eat’ flour on market

Flour is further complicated by the aforementioned practice of consumers eating raw dough products and batters not intended for consumption. In the past there was more concern of contamination coming from raw eggs in such products, but it’s also been proven that flour can be a source. The subject isn’t new for the flour industry even if it hasn’t been a major problem in the past.

“Ready-to-eat” flour has been available at a much higher price point than untreated flour for several years. Most of the flour in this category currently is heat treated. Some of those include Ardent Mill’s SafeGuard (introduced by ConAgra Mills in 2011), which the company said is made by a proprietary process that doesn’t alter gluten functionality, Honeyville’s TempSure All-Purpose Ready-to-Eat flour that also goes through a proprietary process, Siemer Milling Co.’s Heat-Treated soft wheat flours, Bay State Milling’s SimplySafe products and others. It should be noted that whatever treatment is used, microbial content is not eliminated but is significantly reduced.

Also gaining some prominence has been ready-to-eat cookie dough. Nestle first introduced ready-to-eat frozen cookie dough in 2010 after a recall of its Toll House frozen cookie dough. Now there are several companies, such as Pillsbury, Edoughble and others, that offer raw cookie dough that either uses treated flour, pasteurized eggs or other products or don’t use eggs at all. 

Bühler’s ebeam technology

One new method of treating flour under development uses electron beams. Leading in this arena is the Bühler Group with its “ebeam” system, now being tested for the grain milling industry in the United States and Switzerland. The process may be used on all types of flour.

“There is not really anything that works for bread flour without affecting the inherent quality of the flour,” said Gerardo Morantes, Ph.D., director of food safety at Bühler North America. “Nothing seems to be able to do the job. Ebeam doesn’t use heat treatment or any chemicals.”

It doesn’t affect the gluten as does heat treatment and thus can be effective on all-purpose flour used for baking bread, buns and other products that need the qualities provided by gluten.

Bühler in 2015 announced a strategic partnership with Switzerland-based COMET Group, a global leader in ebeam, X-ray and other technologies, while Bühler was well known as an industrial solution provider in the food processing industry, among other things. Bühler utilized its Sortex optical sorting framework for the ebeam process, making it easy to adapt to the cleaning house of a flour mill, Morantes said.

“The performance is there,” he said. “Ebeam is very effective in decreasing the bacteria in the surface of contaminated grains. It has been able to achieve 3-log to 5-log reductions in microbial content.”

The “log” refers to a 10-fold change for every 1-log, thus a 3-log reduction would reduce microbial content to 1,000th and a 5-log to 100,000th of the original level. Most flour buyers require a minimum 3-log reduction, but a 5-log reduction may become the new standard. Both Ardent’s SafeGuard and Siemer’s Heat Treated flours claim validated 5-log pathogen reductions.

“FSMA and consumer concerns are the driving force,” Morantes said. “Every food manufacturing facility that needs to manage the risk of microbial contamination requires a preventative control in their food safety plan. Our aim, what I tell our development group and product managers, is that we need it ASAP. We need it in the field today.”

The ebeam technology was successfully introduced for microbial reduction in spices by Germany-based Kundig earlier this year.

“This process is based on the use of lamps producing low energy electron beams,” the company said. “The prototype that is in operation since the second quarter of 2017 has a capacity of one ton per hour.”

While successful in the spice industry, the key difference between spices and flour is scale, with flour requiring much larger volumes to be processed.

“We are working on scaling up of the technology,” Morantes said. “The estimated cost of operation is going to be lower than other technologies available today.”

There is not yet a set date for the release of ebeam on a commercial basis in the flour industry.

Cold plasma treatment being tested 

Use of cold plasma technology in the food industry also isn’t a new concept, but its potential use in flour milling would break new ground. The potential for cold plasma to cost-effectively reduce contamination and extend shelf life of products, especially meat and produce, was demonstrated several years ago even if it isn’t widely used yet.

“Cold plasma has proven really difficult to scale up (for commercial use),” Morantes said.

But that’s what Labuza and George Annor, Ph.D., a General Mills’ endowed professor in cereal chemistry and technology, also at the University of Minnesota, hope to successfully achieve in the near future. Labuza said a scale-up test using the cold plasma method may be “only months away.”

Plasma is considered the fourth state of matter after solid, liquid and gas. It’s created by applying a spark between several electrodes that causes a reaction with oxygen and nitrogen to form free radicals that in chilled air then alter the DNA and protein of microbes, Labuza said. The process occurs under dry conditions, which allows flour to be treated, ideally as late in the milling process as possible.

“We should be up and running in a couple of months,” Labuza said, adding that it would be six to eight months “at least” before a commercial product could be tested.

A considerable amount of testing remains to be done to collect sufficient data on the cold plasma process, Labuza said. Work had been slowed by a lack of equipment and adequate funding.

“Eventually, we have to verify that any system is giving a 5-log or 6-log sample kill of Salmonella and E. coli over a range of water activity,” he said.

There is a major inherent risk associated with scaling up cold plasma to a commercial level, including the potential of a dust explosion.

“You have to have it in an enclosed environment with a lot of grounding,” Labuza said.

Need for safety continues to grow

AIB’s Dr. Rogers also noted there is some “excitement” around current research about reducing microbial content in the tempering process prior to the milling of grain.

While there was no specific estimate of how much flour (wheat and other grains) is treated for microbial reduction, most in the industry say it is a very small percentage of total production. Cost, scalability and impairment of baking functionality have been key factors discouraging treatment on a broad scale. Further, the fact that flour still is considered a raw ingredient in which a “kill” step generally occurs before it reaches the consumer has limited the need.

At the same time, the fact that flour is a raw ingredient heightens the need for safety as contamination can occur at any step from farm to baker or other food manufacturer to consumer. Flour millers have little if any control at the beginning (in the field) or at the end (consumer level) of the flour “cycle,” but they still are responsible for the safety of their products. To that end, the North American Millers’ Association and the Canadian National Millers Association in early September released a new educational video with the intent of eliminating the safety risk associated with wheat flour.

“From farm to kitchen, the entire wheat industry is committed to best practices for food safety, and this simple and easy-to-use video is designed to help consumers understand and apply proper handling and baking procedures so they can safely enjoy their favorite baked goods,” said James A. McCarthy, president and chief executive officer of NAMA.

Rogers indicated interest in treatment of flour “has been pretty steady” once concern about the two most recent contamination occurrences calmed down. But she noted that microbial reduction remains very important for certain high-risk products such as infant food, refrigerated doughs and inclusions (such as cookie dough in ice cream). She concurred that the new FSMA rules have raised the bar.

“Bakers need to prove their product has a validated kill step,” she said.