Carbon isotope ratio of organic acids in sake and wine by solid-phase extraction combined with LC/IRMS

We developed an analytical procedure for determining the δ¹³C values of organic acids in sake and wine using solid-phase extraction combined with liquid chromatography/isotope ratio mass spectrometry (LC/IRMS). First, the solid-phase extraction (SPE) procedure was performed and various tests were conducted to extract organic acids from alcoholic beverages using the simulated sake sample. Under the optimal SPE procedure, high recovery rates (96-118%) and good accuracies (≤ 0.7‰) were thus achieved for the simulated sake and wine samples. Next, we determined the δ¹³C of organic acid (tartaric acid, malic acid, lactic acid, succinic acid) in 9 sake and 11 wine samples. Finally, the δ¹³C values of lactic acid in nine sake samples suggested that lactic acid had been added during the brewing process. The high correlation between the δ¹³C values of tartaric acid and malic acid in 11 wine samples was consistent with their common source, grapes. This analytical method may help to identify when organic acids have been added to sake and wine and to elucidate the process of organic acid production therein. Graphical abstract.