Thermodynamic and Kinetic Properties of a Red Wine Pigment: Catechin-(4,8)-malvidin-3-O-glucoside

• Tipo: Artigo em Revista Científica Internacional
• Data: 2010

Autores

Frederico Nave (Autor) Outra; Vesselin Petrov (Autor) Outra; Fernando Pina (Autor) Outra; Natercia Teixeira (Autor) Outra; Nuno Mateus (Autor) FCUP; Victor de Freitas (Autor) FCUP

Revista

Título: Journal of Physical Chemistry B

Vol. 114 Nº 1

Páginas: 13487-13496

ISSN: 1520-6106

Editora: American Chemical Society

Indexação

ISI Web of Knowledge - 40 Citações

Scopus - 43 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-003-1T4

DOI: 10.1021/jp104749f

Abstract (EN): Catechin-(4,8)-malvidin-3-glucoside, a red pigment adduct (at acid pH) found in red wine and resulting from the reaction between malvidin-3-glucoside and flavan-3-ols during wine aging, was synthesized. The thermodynamic and kinetic constants of the network of chemical reactions were fully determined by stopped flow: (i) Direct pH jumps, from thermal equilibrated solutions at pH = 1.0 (flavylium cation, AH(+)), show three kinetic processes. The first one occurs within the mixing time of the stopped flow and leads to the formation of quinoidal bases A and/or A(-) depending on the final pH; the second one takes place with a rate constant equal to 0.075 + 33[H(+)] and was attributed to the hydration reaction that forms the pseudobases (hemiketals), B/B(-). The third process is much slower, 2 x 10(-4) s(-1), and is due to the cis-trans isomerization giving rise to a small fraction of truns-chalcones, Ct/Ct(-). (ii) Reverse pH jumps from the thermally equilibrated solution at moderate to neutral pH values back to a sufficiently acidic medium clearly distinguish three kinetic processes: the first one takes place within the dead time and is due to the protonation of the bases; the second process occurs with the same rate constant of the hydration reaction monitored by direct pH jumps and is attributed to the formation of flavylium cation from the B; the last process occurs with a rate constant of 1.8 s(-1) and results from the formation of AH(+) from Ct through B, reflecting the rate of the ring closure (tautomerization). The separation of the hydration from the tautomerization upon a reverse pH jump is only possible because at pH < 1 the former reaction is faster than the last. An identical situation was observed for malvidin-3-glucoside (oenin) for pH < 2.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 10