Food Safety Scientists Crank Up Steam, Radio Waves To Kill Salmonella Amid Spice Recall

MADDIE JOHNSON

FAYETTEVILLE, ARKANSAS

Bacteria can easily hibernate in low-moisture ingredients such as flour and spices, and food scientists have been working on ways to make them safer with novel technologies.

Publication of a food safety study on radiofrequency pasteurization and novel steam technology highlights the recent national recall of black pepper for salmonella risk. The June 3 recall brought low-moisture foods to the forefront of public discussion, showing just because bacteria can’t grow well in dry foods doesn’t mean they don’t pose a threat.

Surabhi Wason was the lead author of the study titled “Radiofrequency inactivation of salmonella in black pepper and dried basil leaves using in-package steaming,” which was published in the Journal of Food Protection. She conducted experiments to develop in-package steaming for enhancing the efficiency of radiofrequency pasteurization of spices and evaluate its impact on the spice quality.

“Radiofrequency, also referred to as macrowave, is a long wavelength, non-ionizing electrical form of energy,” Wason said. “The significant application for radiofrequency technology is in the treatment of dry ingredients where microbes are considered dormant and are in the most difficult state to kill.”

Wason explained that the radiofrequency, or RF, generator creates an alternating electric field between two electrodes, causing the polar water molecules in the material to generate friction, which causes the material to heat rapidly and uniformly.

Wason is a former doctoral student of Jeyam Subbiah, head of the food science department, who served as corresponding author for the study. The food science department is encompassed both by the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture, as well as the Dale Bumpers College of Agricultural, Food and Life Sciences.

Rossana Villa Rojas, assistant professor of practice in the food science and technology department at the University of Nebraska-Lincoln, was a co-author of the study showing that radiofrequency pasteurization and novel steam technology can inactivate salmonella in low-moisture foods, including spices, without significantly compromising quality.

The findings were based on work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2020-67017-33256. McCormick & Company, Inc. supplied low-moisture food materials for the study.

How it works

When a salmonella is identified on a product quality testing, or during a foodborne illness outbreak, the industry has to recall all products since the last cleaning of the plant, Subbiah explained.

“Food processing plants that process low-moisture foods clean less frequently, often once a year, because water in the plant can increase food safety risks,” Subbiah said. “That means the industry has to recall several days to months of production, which could potentially mean that everything on the shelf, and thousands of other products that used that as an ingredient, have to recall, and it’s a huge financial loss. People don’t realize the magnitude of food safety.”

Under traditional methods, low-moisture foods must be exposed to high temperatures for long periods to kill bacteria. Salmonella and other pathogens like listeria can adapt to harsh environments and stay hidden for years, requiring severe processing to be killed, Subbiah said. Without inactivation, the pathogens can begin growing when met with ideal conditions, like the interaction with water that occurs when spices are used in soup.

Baby formula is another low-moisture food that can become dangerous when rehydrated. Subbiah said Cronobacter sakazakii contamination in baby formula can lead to severe illness and death for babies.

With traditional methods, severe heat treatment diminishes aspects of the food quality such as nutrient content and may damage the package because of the generation of steam, Subbiah said. Scientists can also pasteurize these foods through irradiation, or radiation exposure, but consumer acceptance is low, he added.

Subbiah found himself wondering whether the kind of packaging technology that is widely used for foods like microwavable vegetables could be adapted to allow for the same quick heating of dry foods with the additional step of resealing needed before their sale. To prevent steam buildup from eventually bursting packaging, experts developed a one-way valve that releases the steam and then reseals, which is at the heart of Subbiah’s study.

This new valve technology mimics the in-package sterilization of canned goods and uses radiofrequency heating. Conventional heating methods transfer heat to a product through its surface and take longer to reach the center, but radiofrequency heating generates heat inside an entire product mass evenly through friction generated by the vibrating water molecules in an electric field, much like microwave technology. This way, products are pasteurized while they are already in their final packaging and are heated uniformly, avoiding the risk of overheating the edges before heat reaches the center. This in-package processing cuts the risk of contamination that can occur when products are moved between the pasteurization and packaging stages, and foods are safe from contamination until customers open them.

“The gold standard is to package it in the final form and kill the bacteria, like canning,” Subbiah said.

“This technology shows promise for extending to other products like flour, cereal grains offering a robust solution for diverse food sectors," Wason added. "Moreover, one of the key advantages of radiofrequency pasteurization lies in its continuous processing capability. By implementing a conveyor belt system, products can move seamlessly through the RF chamber, ensuring consistent and efficient pasteurization.”

Sticky situation

Subbiah was first inclined to explore this topic of low-moisture food safety after witnessing the costs of a 2007 peanut butter recall.

Recalls for products such as packaged meat require consumers to avoid products processed on a specific day. With dry foods such as peanut butter, though, sanitation of production facilities may happen just once a year, or every few years, to avoid exposing the product to water. This means that in cases of recall, a years’ worth of product, and any other foods that feature it as an ingredient, might pose a health risk for consumers and a financial loss for producers.

The company ended up recalling all peanut butter produced as far back as January 2004, an expected loss of $50-60 million.   ∆

MADDIE JOHNSON: University of Arkansas