On the thermal degradation of anthocyanidins: cyanidin

Cyanidin was studied by direct pH jumps (from equilibrated solutions at very low pH values to higher pH values) and reverse pH jumps (from equilibrated or not equilibrated solutions at higher pH values to very low ones). The kinetic steps of the direct and reverse pH jumps were followed by stopped flow, absorption spectroscopy and HPLC, at different timescales. The pH dependent rate constant of the slower kinetic process to reach the equilibrium follows a bell shaped curve as described for many synthetic flavylium compounds. Unlike anthocyanins, it was proved that there is no pH dependent reversibility in the system, since the chalcone suffers an irreversible degradation process. The mathematical expression to describe the bell shaped behaviour was deduced. These results contribute to explain why in plants glycosylation is crucial for the stabilization of the anthocyanins.