The catabolism of amino acids to a wide range of volatile flavour compounds is amongst the most important series of reactions in the development of cheese flavour. The key enzymes in the degradation of free amino acids appear to be aminotransferases (ATases) from lactic acid bacteria. ATases are intracellular enzymes whose physiological role is in the interconversion of amino acids. These enzymes require pyridoxal-5'-phosphate (PLP) as a co-factor and catalyse the transfer of the amino group of a donor amino acid (leucine in the example below) to an acceptor molecule, usually alpha-ketoglutarate, forming a product alpha-keto acid corresponding to the donor amino acid (alpha-ketoisocaproate in this example) and glutamic acid. The catalytic mechanism of ATases involves two steps: firstly, the amino group of the donor amino acid is transferred to PLP to yield the product alpha-keto acid and enzyme-bound pyridoxamine-5'-phosphate. Secondly, the amino group is transferred from pyridoxamine-5'-phosphate to the acceptor alpha-keto acid, thus regenerating PLP. The alpha-keto acids formed by ATase action are unstable and degrade to a wide range of compounds via enzymatic and/or chemical pathways.
Courses in Cheese Science
Graduate-level courses (6-24 h) on cheese science with an emphasis on the biochemistry of cheese ripening are available are available to companies, universities and research institutes worldwide.
- Cheese Problems Solved (McSweeney, ed., 2007)
- Advanced Dairy Chemistry-3. Lactose, Water, Salts and Minor Consitiuents (McSweeney, Fox, eds., 2009)
- Advanced Dairy Chemistry-2. Lipids (Fox, McSweeney, eds., 2006)
- Advanced Dairy Chemistry-1. Proteins (Fox, McSweeney, eds., 2003)
- Cheese: Chemistry, Physics and Microbiology. Vol. 2. Major Cheese Groups (Fox, McSweeney, Cogan, Guinee, eds., 2004)
- Cheese: Chemistry, Physics and Microbiology. Vol. 1. General Aspects (Fox, McSweeney, Cogan, Guinee, eds., 2004)
- Fundamentals of Cheese Science (Fox, Guinee, Cogan, McSweeney, 2000)
- Dairy Chemistry and Biochemistry (Fox and McSweeney, eds., 1998)