Comparing the Chemistry of Malvidin-3-O-glucoside and Malvidin-3,5-O-diglucoside Networks

The kinetics, thermodynamics, and degradation of malvidin mono- and diglucosides were studied following a holistic approach by extending to the basic medium. In acidic conditions, the reversible kinetics of the flavylium cation toward the equilibrium is controlled by the hydration and cis-trans isomerization steps, while in the basic medium, the OH- nucleophilic addition to the anionic quinoidal bases is the slowest step. There is a pH range (transition pHs), between the acidic and basic paradigms, that includes physiological pH (7.4), where degradation reactions occur faster, preventing the system from reaching the equilibrium. The transition pH of the diglucoside is narrower, and in contrast with the monoglucoside, there is no evidence for the formation of colored oligomers among the degradation products. Noteworthy, OH- addition in position 4 to form B42-, a kinetic product that decreases the overall equilibration rate, was observed only for the diglucoside.

Descrição

financed by national funds fromFCT/MCTES and by the AgriFood XXI I&D&I project(NORTE-01-0145-FEDER-000041) cofinanced by EuropeanRegional Development Fund (ERDF), through the NORTE2020 (Programa Operacional Regional do Norte 2014/2020. Gulbenkian Foundation grant no 219201 and Meritgrant 2020�INAGBE, Angola (AC).

Palavras-chave

anthocyanins degradation rates kinetics malvidin monoglucoside and diglucoside malvidin monoglucoside dimers physiologic pH stopped-flow General Chemistry General Agricultural and Biological Sciences