Martin Pour Nikfardjam

Effect of Molecular Environment on the Formation Kinetics of Complexes of Malvidin-3-O-glucoside with Caffeic Acid and Catechin

The formation kinetics of malvidin-polyphenol copigmentation complexes was studied in water-ethanol mixtures by time-dependent recording of the photoluminescence (PL) signal of malvidin. Two reaction channels were examined according to the order of complex formation. Both channels end with the same malvidin-polyphenol complexes formed in binary mixtures of water-ethanol. However, in the first case, the malvidin-polyphenol complexes are formed in water first, and then their solvation shells are altered according to the changed composition of the bulk solutions after the aqueous solution is diluted with ethanol. In the second case, the stock solutions are prepared as binary solvent mixtures; therefore, the bicomponent solvation shells of the interacted species are formed prior to molecular association. Our results show a faster formation of the complexes in the former case. Evaluation of the Arrhenius parameters of the reaction shows that the activation energy of the first reaction channel is lower and the frequency factor is higher, supporting a higher reaction rate. These observations are applicable to a wide range of chemistry where the molecular environment is composed of binary solutions. In particular, it has significant consequences for winemaking procedures, where one method of color improvement is based on the association of the species examined in this work.

The Effect of Temperature on the Color of Red Wines

UNLABELLED The effect of increased temperature on the color of red wines was studied due to its importance during storage and transport. The chemical reactions induced by elevated temperature were investigated by measuring the UV-VIS spectra. The temperature of the wines was increased from its common storage temperature (about 14 °C) to higher temperatures (t= 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C) and the UV/VIS spectra were recorded during several hours. The spectral changes obtained indicate the presence of quasi-first-order chemical processes justifying determination of the activation energies using their temperature dependence. The determined decay values (Villányi Portugieser: E(VP) (a,420 nm) = 90.02 kJ/mol, E(VP) (a,520 nm) = 34.18 kJ/mol, E(VP) (a,620 nm) = 54.55 kJ/mol; half-life values of 46.5 d [25 °C] and 9.5 d [35 °C] at 420 nm; 4.67 d [25 °C] and 2.0 d [35 °C] at 520 nm; 9.5 d [25 °C] and 2.4 d [35 °C] at 620 nm; Bikatory wine: E(Bk) (a,420 nm) = 82.07 kJ/mol and half-life values of 41.35 d [25 °C] and 4.001 d [35 °C] at 420 nm) of these reactions highlight a considerable change in the quality of wines stored for a few hours at elevated temperatures. Depending on polyphenol composition the wines show different half-life with regard to their color stability and browning reactions. Higher polyphenolic content helps to stabilize the wine against detrimental temperature effects. PRACTICAL APPLICATION This research can be applicable to estimate the optimal temperature of red wines during storage and transport.