Content of free amino acids and biogenic amines during the maturation of Casín cheese: Feasibility of using VIS-NIRS spectroscopy for their quantification.

Casín cheese is a traditional Spanish raw-milk cow's milk cheese with PDO status that is characterized by intense proteolysis during ripening. In this study, the evolution of free amino acids, biogenic amines and ammonium ion during the ripening of Casín cheese was evaluated, and the feasibility of using a portable Vis-NIR instrument (350-2500 nm) combined with chemometrics for their quantification was assessed. Ninety cheese samples of different batches from three manufacturers were analyzed at five stages of ripening (from 3 to 60 days). Quantification of amino acids and derivatives was performed using ultra-high-performance liquid chromatography after derivatization with diethyl ethoxymethylenemalonate. Calibration models were developed using modified partial least squares regression. Total free amino acids, the ammonium ion and biogenic amines peaked on day 30, with tyramine and histamine being the most abundant amines. The chemometric models achieved excellent predictive performance during external validation (N = 18) for phenylalanine (RSQ = 0.92, RPD = 3.37), valine (RSQ = 0.86, RPD = 2.40), serine (RSQ = 0.92, RPD = 2.14), tryptophan (RSQ = 0.80, RPD = 2.12), putrescine (RSQ = 0.83, RPD = 2.42), histamine (RSQ = 0.82, RPD = 2.20), and ammonium ion (RSQ = 0.88, RPD = 2.77). Under the conditions of the study, portable Vis-NIR spectroscopy proved to be a reliable, rapid, and non-destructive tool for analyzing biogenic amines in cheese and monitoring the degree of ripening in traditional artisanal Casín cheese.