Occurrence of free D-aminoacids in milk and in typical derived cheeses

Free D-aminoacids (D-AA) have been detected in raw milk and typical derived cheeses by enantiomeric separation with RP-HPLC and fluorescence detection. The dairy products were treated with ethanol and protein precipitated by addition of picric acid. After centrifugation, the free amino acids were purified on a cation exchange resin. The occurrence of D-AA in milk and cheese, in particular D-asp, D-glu and D-ala, was probably due both to the lysis of bacterial cell walls and to the natural fermentation. Possible technological and nutritional aspects of the presence of D-AA in dairy products are discussed.