Accumulation of non-proteolytic aminoacyl derivatives in Parmigiano-Reggiano cheese during ripening

For the first time, the identification of N-γ-glutamyl-, N-pyroglutamyl- and N-lactoyl-amino acids in Parmigiano-Reggiano cheese is reported. Their structures were assigned by electrospray mass spectrometric analysis and demonstrated for several compounds by the synthesis of authentic specimens and sample spiking. The comparison with the synthesised compounds also allowed the determination of their absolute stereochemistry (l,l), which indicated a common enzymatic origin. All these molecules were shown to accumulate in Parmigiano-Reggiano during ripening, probably because of a resistance to proteolysis due to their unusual structures. Thus, these compounds can be used as markers of ripening time and may be involved in the development of the pleasant flavour of aged cheeses. Their presence in other cheeses was also demonstrated.