D-alanine (D-Ala), D-aspartic acid (D-Asp) and D-glutamic acid (D-Glu) are important constituents of the cell walls of bacteria responsible for fermentation processes, and have been detected in several fermented foods, such as cheeses, yogurt and vinegar (Palla et al. 1989; Brückner & Hausch, 1990; Dossena et al. 1991; Brückner et al. 1992; Gandolfi et al. 1992). In particular, D-amino acids have been found, free and abundant, in cheeses requiring long ripening periods (1–2 years; Santaguida et al. 1995). Their presence in cheeses could be related mainly to lysis of the bacterial wall, to which short-chain D-amino acids are bound, but also to the activity of bacterial racemases (Adams, 1972), which convert free L-amino acids generated during proteolysis. The content of these D-amino acids and the D:L ratio have been recently proposed as indicators of ripening and for quality assessment of Parmigiano Reggiano and Grana Padano cheeses (Marchelli et al. 1997).

The aim of the present study was to determine D-amino acids in cheeses with shorter ripening periods to evaluate whether they could be useful as indicators of ripening and for quality assessment. The work was carried out with Montasio, a typical cheese produced in north-east Italy using traditional methods. Montasio is a semi-hard cheese produced from unpasteurized milk, cooked at 44–46 °C and consumed after at least 2 months ripening. This study represents an extension of previous work on free amino acid contents and ripening in semi-hard cheeses (Innocente, 1997).