Reaction kinetics of the acetaldehyde-mediated condensation between (-)-epicatechin and anthocyanins and their effects on the color in model wine solutions

The reaction kinetics of five primary wine anthocyanins (cyanidin-3-O-glucoside, peonidin-3-O-glucoside, delphinidin-3-O-glucoside, petunidin-3-O-glucoside, and malvidin-3-O-glucoside) and (-)-epicatechin with the presence of acetaldehyde were evaluated in model wine solutions at a range of varying temperatures (25, 35, 45, and 55 degrees C). The loss of anthocyanins followed first-order reaction model, while the formation of two isomers of anthocyanin ethyl-linked (-)-epicatechin was fitted to zero-order reaction model. The rate constant (k) showed that petunidin-3-O-glucoside was the most reactive anthocyanin, followed by the two 3',4'-substituted anthocyanins (peonidin-3-O-glucoside and cyanidin-3-O-glucoside), while the least reactive were another two 3',4',5'-substituted anthocyanins (malvidin-3-O-glucoside and delphindin-3-O-glucoside). The activation energies (E-a) indicated that the formation of ethyl-linked products from methylated anthocyanins were more sensitive to temperature than that from hydroxylated anthocyanins. Thermodynamic parameters showed a non-spontaneous and endothermic process. Besides, the evolution of the visible color of reaction solution was affected by the stability of anthocyanins and the formation of ethyl-linked products.