Application of UHPLC for the simultaneous analysis of free amino acids and biogenic amines in ripened acid-curd cheeses

A new UHPLC method for the simultaneous determination of amino acids and biogenic amines in a single run, and its first application to profile ripened acid-curd cheeses was presented. After pre-column derivatization with 6-aminoquinolyl-N-hydroxy succinimidyl carbamate (AQC), 23 amino acids and 15 amines were separated in 9min only (12min total run time), and eluates monitored using their UV response at 249nm. Limits of detection (0.05-0.29mg/100g) and quantification (0.16-0.97mg/100g), repeatability for sample preparation (1.0-6.1% RSD) and method recoveries (83-120%) were found suitable for cheese analysis. In total, 47 acid-curd cheeses classified into sub-groups like cooked, Quargel-type or grey cheeses were analyzed for their free amino acid and amine (histamine, tyramine, putrescine, cadaverine, and tryptamine) contents, which (as expected) were highlighted by a great variability. Total free amino acid levels ranged between less than 100 and more than 4000mg/100g (median 567mg/100g), implying that for some cheeses less or not ripened/fresh quark was used for production or, in contrast, a higher degree of proteolysis had occurred. For the sum of biogenic amines, median concentration was determined at 7.0mg/100g, while only 5% of all cheeses had levels higher than 161.9mg/100g. Thus, the obtained results suggest quite acceptable biogenic amine levels for (mostly underrated) ripened acid-curd cheeses, although partly exceptional high concentrations (>250mg/100g) were indeed observed in individual samples.