Color formation during caramelization in ascorbic acid based systems

Currently, two-component systems based on L-ascorbic acid, used as sources of biologically active food additives, are of particular interest in food technology. The investigation presents the results of research on the mechanisms and dynamics of chromophores formation in caramelization processes in 40 % ethanol medium; the subjects of study were L-ascorbic acid (Asc) and its equimolar mixture with D-glucose (Glc). The formation of colored substances in both systems was identified by molecular spectroscopy at the end of thermostatting the solutions (50 °С, 1.5 h) and their subsequent aging (25 °С) for 30 days. The calculation of the color indexes of the water-ethanol systems Asc and Asc + Glc showed an increase in the intensity of chrominance during caramelization of L-ascorbic acid in the presence of D-glucose, indicating the formation of a longer and more stable chromophore system in the double system, which is confirmed by the nature of the electronic spectra. Comparative analysis of the vibrational spectra of the test solutions shows the presence of bands characteristic of conjugated C=O + C=C-combinations, second derivatives of bands in the region of multiple bonds stretching vibrations identify in the spectrum of the double system an intense signal of 1654 cm-1 related to O=C-C(OH)=C-fragments. The latter indicates greater stability of the chromophore components of the structure formed by the co-caramelization of the double system components. Condensation of Asc and Glc transformation products leads probably to a number of colored products, one of which is substituted δ-lactone, which includes hydroxy-α,β-enone fragments. It is assumed that the latter are stabilized by R-substitution, providing a greater length and stability of the chromophore system that forms color in comparison with the products of caramelization of ascorbic acid. Further study of the properties of caramel compositions based on ascorbic acid (light resistance, toxicity, antioxidant properties) will allow the development of affordable and environmentally friendly polyfunctional pigments.