Newly identified enzyme reduces bitterness in cheese

Adding it to starter culture could make a more consistent product and save money

A UW-Madison food scientist is using new technology to tackle an old problem in cheesemaking – and the solution could mean both a bigger market for the state’s dairy producers and reduced costs for cheesemakers.

One of the major expenses in cheesemaking is the cost of storing cheeses as they age and develop their distinctive flavors, says Jim Steele, a food scientist with the College of Agricultural and Life Sciences. Cheddar takes six months to a year to mature, while Parmesan takes a full year. During that time off-flavors and bitterness, the most common Cheddar defects, may develop.

“We’ve identified an enzyme that plays a critical role in reducing bitterness in cheese,” says Steele. “If the bacteria in the starter culture produced this enzyme cheesemakers would save money and ensure a more consistent product.”

According to Steele, inconsistent quality reduces producers’ ability to market their cheese to commercial food processors. “Food processors need to be able to produce a consistent product-that’s why they are very discerning of quality, much more so than consumers buying cheese for their table.” Steele says.

Cheesemaking begins when processors add starter cultures to warm milk. The cultures contain strains of bacteria that produce enzymes that break down the proteins in milk, giving the cheese flavor and helping it ripen more quickly. In addition to the starter culture, cheesemakers sometimes use a culture of the bacterium Lactobacillus helveticus to reduce bitterness and enhance flavor. However, if the genes that produced the key enzyme were part of the bacteria in the starter culture, cheesemakers would reduce costs by not having to use additional cultures.

Steele, a geneticist by training, wanted to determine which enzymes in Lactobacillus are responsible for avoiding the development of bitter flavor. Steele and his colleagues spent 12 years identifying and characterizing 11 bacterial enzymes that might have a role in reducing bitterness. His research group constructed numerous so-called “knockout bacteria,” which are identical to the original Lactobacillus strain except that they lack the gene needed to produce a particular enzyme. The researchers then compared the strains in cheese trials to find out whether the enzyme that had been knocked out affected bitterness.

After the cost of conducting genomic research decreased, Steele’s research group was able to sequence almost all of the 2,400 genes in Lactobacillus. This information allowed them to identify, in just six months, an additional twelve genes that might have a role in reducing bitterness. Then the group used the “knockout” strategy to select the most important gene.

Now that Steele’s group has identified the key enzyme for reducing bitterness, the researchers can add the gene that produces it to the bacteria in the starter culture. ‘We are applying for a patent soon, and anticipate the modified starter culture being commercially available in less than two years,” Steele says.

In the future, Steele plans to use other techniques to determine how Lactobacillus produces more complex flavors, such as nuttiness. “Using microarray technology, we will put the bacteria under cheese-like conditions and study which genes make proteins,” explains Steele. “That will allow us to narrow down the number of genes involved in flavor production by at least ten-fold.”

Steele credits the University of Wisconsin-Madison’s “extraordinary environment,” which allowed him to collaborate with other experts in this cross-disciplinary research. “I was able to work with Mark Johnson, a top-notch cheesemaker and dairy microbiologist at the Wisconsin Center for Dairy Research, and with Fred Blattner’s laboratory, which is an international leader in genomic studies.”