Mass spectrometry imaging of the distribution of generated compounds during ripening in Camembert cheese produced...

In this study, changes in the taste compounds of Camembert cheese produced via 2 typical procedures during ripening were investigated. Changes in the pH, contents of free amino acids and lactic acid using HPLC-MS, and sensory properties (sourness and umami) of the cheese samples were determined during ripening (after 1, 11, 19, and 28 d). The distribution of lactic acid and Glu among the cheese matrices was analyzed by MALDI-TOF MS imaging (MSI). Lactic acid and Glu detection was performed using the derived product ion of m/z = 252.2 (positive ion mode) and precursor ion of m/z = 89.1 (negative ion mode), respectively. Glutamic acid was derivatized to enhance the MS ionization efficiency and selectivity by 2,4,6-trimethylpyrylium tetrafluoroborate. Cheese samples were produced using 2 methods: the traditional procedure (T-sample) and the stabilized procedure (S-sample). The S-sample was obtained to maintain a higher pH than the traditional procedure after incubation using starter thermophilic lactic acid bacteria. The changes in the pH and content of the total free amino acids and lactic acid in the S-sample during ripening were lower than those of the T-sample. The sensory scores of sourness at d 1 and umami at d 19 and 28 of the T-sample were higher than those of the S-sample, indicating that the flavor intensity of the T-sample was due to the higher generation of taste-related compounds during ripening. The MSI showed that the lactic acid content decreased during the ripening period, and the MS intensity of Glu increased with the ripening period. The changes of these compounds were more notable at the surface than at the central part of the Camembert cheese, which may be due to the activation of white mold on the surface. The MSI successfully revealed the spatial and temporal dynamics of key flavor compounds, thereby demonstrating its applicability in evaluating the ripening processes in white mold cheeses.