Quantification of Amadori products in cheese

To obtain basic information about the extent of the early Maillard reaction in commercially available cheese varieties of varying degrees of maturity, Amadori products (APs) formed between reducing sugars and the ε-amino group of lysine (ε-APs) or the α-amino of selected amino acids (α-APs) were analyzed. APs were determined as the corresponding N-(2-furoylmethyl) amino acids (FMAAs) after acid hydrolysis using RP–HPLC with UV-detection as well as mass spectroscopy. Identification of the FMAAs resulting from the α-APs of lysine, valine, leucine, and isoleucine was achieved for the first time for cheese samples. The content of furosine, which is a hallmark for ε-APs, ranged from to 3–75 mg/100 g protein corresponding to 24–591 μmol ε-AP/100 g protein. ε-AP levels declined during ripening in all investigated cheeses, depending on the cheese type and stage of maturation. The mean content of four α-APs ranged from 138 to 681 μmol/100 g protein. Lowest concentrations were found in long-term ripened cheese samples, indicating a putative degradation of α-APs and ε-APs during advanced stages of maturation. The ratio of α-APs to ε-APs might be a useful indicator of cheese ripening.