–by Liz Morrison
Related Information
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>What is Listeria
>AURI collaborates on dairy research
The salt content of cheese may be lowered without compromising food safety, new research shows.
Salt in cheese limits the growth of harmful bacteria. But, reducing the salt content of American cheese slices did not increase the survival of a virulent pathogen, Listeria monocytogenes, according to a University of Minnesota study, sponsored by AURI and the Midwest Dairy Association.
“This study provided the first actual data on Listeria cell survival on commercially available, sodium reduced American processed cheese,” says study leader Francisco Diez-Gonzalez, University of Minnesota professor of food science and nutrition. “Our results indicated that there were no differences in L. monocytogenes survival patterns on slice-on-slice or individually wrapped process American cheese at different temperatures.”
This finding is important because Listeria can cause serious foodborne illness, says Charan Wadhawan, AURI senior food scientist in Crookston. The pathogen, which is common in the environment, is destroyed by pasteurization, but can infect cheese through cross-contamination at the plant or after products leave the factory.
Although processed cheese has rarely been involved in Listeria outbreaks, a recall of processed Swiss cheese in Canada in 2010 shows that the potential for contamination exists. Now, the new research assures consumers that sodium reduced processed cheese carries no more food safety risk than regular cheese, Wadhawan says.
Reducing salt consumption in processed food
The development of sodium reduced processed cheese is part of a larger food industry drive to cut the salt content in processed foods.
“Most Americans consume far more sodium than health experts recommend,” Wadhawan says, and that can lead to health problems like high blood pressure. The federal Dietary Guidelines for Americans recommend limiting sodium intake to less than 2,300 milligrams (mg) a day — the amount of sodium in a single teaspoon of table salt. For African-Americans, people over 51, and those who have high blood pressure, diabetes or kidney disease, the daily recommendation is even lower — 1,500 mg.
The average American consumes about 3,400 mg of sodium a day, and that’s not just from table salt, Wadhawan says. The main way that salt sneaks into your diet is through processed foods. “About 75 percent of Americans’ salt intake comes from packaged and processed foods.” Cheese contributes about 8% of sodium in American diets, and is the third largest source of salt from processed foods, Wadhawan says.
The National Sodium Reduction Initiative aims to curb Americans’ salt habit, and has obtained pledges from many major food companies to work on reducing sodium in processed foods.
The dairy industry is a key part of this effort, says Mary Wilcox VP Business Development for the Midwest Dairy Association (MDA), Minnesota’s dairy check-off organization. In 2009, U.S. cheese makers formed the Cheese and Sodium Best Practices Task Force to work on ways to reduce sodium in cheese.
This is a complex challenge, involving far more than simply putting in less salt. “Reducing sodium in processed cheese requires innovative, research-based solutions,” says Bill Graves, senior vice-president of product research at the Dairy Research Institute. “Sodium chloride performs critical functions in making safe, good quality and good-tasting cheese.”
Salt contributes to flavor and texture, melting characteristics, and shelf life, Wilcox explains. Salt also “limits the growth of pathogenic — or unwanted — bacteria” and retards spoilage.
One of the things manufacturers are doing to reduce the sodium content of processed cheese is to substitute potassium chloride for sodium. “These changes require a thorough evaluation of the potential food safety implications,” Diez-Gonzalez says. His recent research on Listeria in sodium reduced processed cheese slices is part of the industry’s efforts to understand these food safety risks, Wilcox says.
Research trials at the U of M
The research was performed in 2011 and 2012 at the University of Minnesota’s Food Safety Microbiology Laboratory in St. Paul. The replicated trials included three commercial brands of processed American cheese and 
their sodium reduced counterparts, in which some sodium had been replaced by potassium. Sodium content in the reduced sodium processed cheeses was 28 percent to 43 percent less than in the regular cheese. Both individually-wrapped processed cheese slices and bulk processed cheese slices were tested.
The processed cheese slices were inoculated with five different strains of Listeria, then evaluated for pathogen survival at four different temperatures over 60 days.
“Overall, no clear distinguishable patterns of Listeria survival were observed on the sodium reduced processed cheese compared to regular cheese,” Diez-Gonzalez says.
This study was one of many initiatives organized by AURI to help Minnesota’s cheese industry with research and development, says Jennifer Wagner-Lahr, AURI senior director of innovation. The state has 41 companies that manufacture cheese — many of them producer cooperatives. About 85 percent of Minnesota milk production is made into cheese, Wagner-Lahr says. That’s why AURI is working with the cheese industry to “find innovative solutions for today’s and tomorrow’s problems.”
Industry gradually reducing sodium in some cheeses
Cheese makers are taking a gradual approach to reducing sodium in cheese, says Donna O’Connor, AURI Food and Nutrition Scientist. Recent innovations, such as a new rapid test for measuring sodium during cheese production, are helping manufacturers tighten control of the salt content, too.
Sodium reduced processed cheeses are now being sold in grocery stores, although they are not usually labeled as reduced sodium, O’Connor says. Minnesota cheese processors are providing sodium reduced processed cheese to schools, to help meet federal mandates for less salt in school meals.
Some examples of sodium reduced processed cheeses now on the market include:
•Kraft Grated Parmesan: 10% salt reduction
•Velveeta: 10% salt reduction
•Kraft Singles American Slices: 18% salt reduction
•Mozzarella for schools: 25% salt reduction
•Most processed cheese for schools from the USDA: 25% salt reduction
