Identification of bitter-taste compounds in class-III caramel colours

Caramel colours become one of the most widely used colorings in various foods and beverages due to their total miscibility with water and great coloring properties by containing colloidal aggregates. Bitterness in caramel colours can negatively influence their acceptability. The sequential solvent extraction (SSE) and semi-preparative liquid chromatography (SP-LC) combined with the taste dilution analysis were applied to identify the most intense bitter-tasting compounds in class-III caramel colours. Four main compounds with the highest bitterness intensity were isolated and structurally elucidated based on high resolution-electrospray ionization-mass spectrum (HR-ESI-MS), nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrum (GC-MS): 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP), 5-(hydroxymethyl) furfural (HMF), furfural and 5-methylfurfural (MF). The threshold concentrations of DDMP, HMF, furfural and MF were 14.3, 30.0, 4.4 and 17.5μmol L −1 , respectively. Furthermore, two volatile bitter compounds were identified: [5-(di-methoxymethyl) furan-2-yl] methanol (DMFM) and 2,3,4,4-tetramethyl-pentane-1,3-diol (TMP). Based on the composition of the caramel colours and the structures of these compounds, Maillard reaction was supported to generate these bitter compounds in caramel colour-III.