Lactones formation during monosaccharide's caramelization in ethanolic-aqueous solutions

Abstract

δ-Lactone's formation processes in alkaline aqueous-ethanolic monosaccharide systems have been studied using derivative FTIR spectroscopy. Three monosaccharides-D-glucose (Glc), D-galactose (Gal), D-mannose (Man) show some differences in lactonization pathways. Two parallel reactions such as enolate Spengler-Pfannenstiel degradation and Cannizzaro reaction of α-dicarbonyl compounds lead to various saccharinic acids, which may form lactones as a part of condensed caramel structure. Second derivative spectra in region of 1760-1700cm-1 shows six-member "lactone"bands near 1738cm-1 (Gal, Man) and 1745, 1755cm-1 (Glc) for 1 hour thermosttating products, as soon as for 1.5 hours thermostatted products "lactone"bands at 1747cm-1 registered only for mannose and at 1738cm-1 for all systems. FTIR bands position suggests the including lactone's fragments in caramel condensed structure. Spectra character can be explained by the difference in enolization rate and conformation type of monosaccharides and its six-member lactones. Formation of free D-glucono-δ-lactone in reactions confirmed by the FTIR spectra analysis of chromatographic zones extracts with Rf values of 0.20-0.40, at the same time δ-lactones of mannose and galactose are not isolated in pure form.