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Enzyme to reduce bitterness in cheese.

Bitterness in cheese occurs when there is an imbalance of the production of bitter peptides by protease and endopeptidase enzymes, and involves their removal by exopeptidase enzymes. Scientists at the University of Wisconsin-Madison are using new technology to tackle cheese bitterness. Their solution could mean both a bigger market for 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. 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. Wisconsin investigators have identified an enzyme that plays a critical role in reducing bitterness in cheese.

In addition to a starter culture, cheesemakers sometimes use a culture of Lactobacillus helveticus to reduce bitterness and enhance their product's flavor. However, if the genes that produced this critical enzyme were part of the bacteria in the starter culture, cheesemakers would lessen their costs by not having to use additional cultures.

Wisconsin scientists wanted to determine which enzymes in Lactobacillus are responsible for avoiding the development of bitter flavor. The researchers spent 12 years identifying and characterizing 11 bacterial enzymes that might have a role in reducing bitterness. They constructed numerous knockout bacteria, which are identical to the original Lactobacillus strain, except that they lack the gene needed to produce a particular enzyme. The researchers compared the strains in cheese trials to find out whether the enzyme that had been knocked out had affected bitterness.

The 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 12 genes that might have a role in reducing bitterness. Then the group used the knockout strategy to select the most important gene. Now the team has identified the key enzyme--PepO2--for reducing bitterness. The researchers can add the gene that produces it to bacteria in the starter culture. They are applying for a patent and anticipate the modified starter culture would be commercially available in less than two years. They plan to produce a food-grade vector and work on methods for overexpression of this enzyme in Lactococcus lactis.

The investigators also plan to use other techniques to determine how Lactobacillus produces more complex flavors, such as nuttiness. Using microarray technology, they'll put the bacteria under cheese-processing-like conditions and study which genes make proteins. That will allow them to narrow down the number of genes involved in flavor production at least tenfold.

Further information. Jim Steele, University of Wisconsin-Madison, Department of Food Science, 125 Babcock Hall, Madison, WI 53706; phone: 608-262-5960; fax: 608-262-6872; email:
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Publication:Emerging Food R&D Report
Date:Feb 1, 2003
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