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 9 min only (12 min total run time), and eluates monitored using their UV response at 249 nm. Limits of detection (0.05–0.29 mg/100 g) and quantification (0.16–0.97 mg/100 g), 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 4000 mg/100 g (median 567 mg/100 g), 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 7.0 mg/100 g, while only 5% of all cheeses had levels higher than 161.9 mg/100 g. Thus, the obtained results suggest quite acceptable biogenic amine levels for (mostly underrated) ripened acid-curd cheeses, although partly exceptional high concentrations (>250 mg/100 g) were indeed observed in individual samples.