Characterisation of caramel-type thermal decomposition products of selected monosaccharides including fructose, mannose, galactose, arabinose and ribose by advanced electrospray ionization mass spectrometry methods

The chemical analysis of caramel, formed upon heating of carbohydrates, remains a significant challenge due to the complexity of the resulting product mixture. Identification of the products formed upon heating of monosaccharides including fructose, mannose, galactose, arabinose and ribose is essential to understand the composition and properties of carbohydrate-rich processed foods. In this work, we report on the use of combined mass spectrometry techniques, including high performance liquid chromatography and electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). The composition of the obtained caramel was examined by high resolution mass spectrometry along with van Krevelen and Kendrick analysis. We found that caramel is composed of oligomers with up to six carbohydrate units formed through unselective glycosidic bond formation, their dehydrated products by losing up to eight water molecules, hydrated products and disproportionation products. An accurate mass measurement and subsequent fragment ion studies of all caramel samples (around 40 compounds) can thus be identified. Glycosidic bond and ring cleavages of sugar moieties were the major observable fragmentation pathways during this experiment. The innovative analytical strategies for the complex mixture analysis used provide a comprehensive account of the chemical composition of caramel, one of the most popular dietary materials over the world.