Improve development of cheese flavors.

The lack of basic knowledge on how to control flavors formed from cheese microorganisms limits the possibility for flavor-specific product development. A better knowledge of these processes will help improve the competitiveness of the dairy industry. European researchers are trying to determine major degradation routes of amino acids released during proteolysis, which can lead to the formation of specific cheese flavor components.

Investigators are examining selected isolates of starter and non-starter lactic acid bacteria (LAB) from various European types of cheeses--cheddar, Gouda, Serra, Manchego, St. Paulin, Emmantaler and Danbo--as to their ability to metabolize amino acids into volatile flavor compounds.

Many cultures have been screened for flavor-forming ability and for amino acid-converting enzymes (AACEs). A range of AACEs are present in LAB and other food-grade bacteria, some with low and some with high activity. Differences between genera (Lactococcus, Lactobacillus, Brevibacterium) may explain variations in cheese-ripening ability.

Researchers have screened both in-vitro (buffer systems) and in-vivo (cheese paste model system). These and other tests suggest that certain pathways are more important than others for forming cheese flavor. These pathways involve the conversion of methionine, aromatic amino acids and branched-chain amino acids. Transamination is an important initial step in flavor development. This is followed by further enzymatic and chemical conversions.

A transaminase of L. lactis has been purified and characterized. Researchers used the N-terminus to isolate the gene coding for this enzyme, making it possible to isolate the gene itself. Inactivation of the aromatic amino acid transferase gene in L. lactis led to a 90% to 95% reduction in aminotransferase activity for aromatic amino acids and a 25% to 50% reduction for methionine and leucine. The former indicates that this conversion pathway seems to be the dominant one in L. lactis, and the latter indicates that other pathways and enzymes exist in L. lactis for methionine and leucine conversion.

These and other data show that various pathways overlap due to nonspecific enzymatic activities. Further studies are needed on the regulation and physiology of these enzymes to find how pathways can potentially be engineered. Further information. G. Smit, NIZO Food Research, PO Box 20, 6710 BA Ede, The Netherlands; phone: [phone]; fax: [phone]; email: [e-mail].