Kokumi-active glutamyl peptides in cheeses and their biogeneration by penicillium roquefortii

Recently, a group of γ-glutamyl dipeptides, but not the R-glutamyl dipeptides, were found to induce the attractive kokumi flavor of matured Gouda cheese. In the present investigation, the spatial distribution of R- and γ-glutamyl dipeptides in Gouda cheese wheels and the concentration of these peptides in other cheese types were determined by means of HPLC-MS/MS. Among all cheeses investigated, by far the highest γ-glutamyl peptide concentration (3590 μmol/kg) was found for Blue Shropshire, a blue-veined cheese. To check whether the γ-glutamyl transferase (GGT) from Penicillium roquefortii is involved in γ-glutamyl peptide production in this cheese, the GGT activity was measured and γ-glutamyl peptides were analyzed in liquid cultures of mold isolated from Blue Shropshire as well as single P. roquefortiii strains incubated with the γ-glutamyl donor L-glutamine and the candidate substrates L-glutamic acid, L-histidine, L-leucine, and L-methionine. Being well in line with the GGT activity found in Blue Shropshire, P. roquefortii was found for the first time to produce and secrete γ-glutamyl peptides. Among the amino acids tested, L-methionine was found as a preferred γ-glutamyl acceptor; for example, γ-Glu-Met was produced in yields of about 50 mmol/ mol and [ ²H ₃]- γ-Glu-Met was obtained when [ ²H ₃]-L-methionine was used as substrate amino acid