Charge equilibria and pKa of malvidin-3-glucoside by electrophoresis

• Author(s): Asenstorfer, Robert; Iland, Patrick; Jones, G.; Tate, Max;
• Abstract: Paper electrophoresis has been used over the pH range 1.2 to 10.4 to measure apparent pKa values for malvidin-3-O-glucoside of pKa1 1.76+-0.07, pKa2 5.36+-0.04, and pKa3 8.39+-0.07. Using solvent partitioning between buffered aqueous solutions and n-octanol, several micro-pKa constants for malvidin-3-O-glucoside were also identified, highlighting the complex nature of malvidin-3-glucoside equilibria. As a nonspectrophotometric procedure, the charge-dependent electrophoretic mobility method provided independent information on the net charge and color of anthocyanin species at wine pH (ca. 3.6). At this pH, the color of malvidin-3-glucoside in red wines is consistent only with the uncharged quinonoidal base as a major colored component of the equilibria.
• Publication Date: Jul 2003
• Journal: Analytical Biochemistry