13C{1H} NMR-Guided Identification of a New Marker of Caramel Color IV.

Thirty-one Sulfite Ammonia Caramel (Caramel Color IV) samples from China and one from the United States were analyzed by NMR spectroscopy. Characteristic signals at δ 31.6 and 55.7 ppm were observed in all but one Chinese sample and also in the US sample. Guided by these signals, the corresponding compound was isolated via methanol extraction, gel filtration, and reversed-phase C18 chromatography. It was characterized by NMR and HRMS as sodium trans-5-(hydroxymethyl)-2-oxotetrahydrofuran-4-sulfonate; its relative configuration was confirmed by synthesis, whereas the absolute (4S,5R)-configuration is tentatively assigned. This compound represents the second characteristic small-molecule signature identified in Caramel Color IV, after the known marker 4-methylimidazole. Its widespread presence across most analyzed samples suggests its potential as a candidate marker for detection and characterization of Caramel Color IV products, though further validation with a broader sample set is warranted.