Effect of Sodium Perchlorate on Flavylium Salt-Carbinol Base Equilibrium in Acidic Solutions

Studies on Qualities of Grape Juice (Part 8)

Abstract

The effect of sodium perchlorate on the spectral and polarographic behavior of malvidin-3, 5-diglucoside chloride was studied in the acidic solutions. (1) Addition of sodium perchlorate to malvidin-3, 5-diglucoside solution (pH 2.3) caused the increase of absorbance at 520 and 275nm.(2) Addition of sodium perchlorate to malvidin-3, 5-diglucoside in citric acid-disodium hydrogen phosphate buffer (pH 4.0) caused the increase of the first wave (-0.46 V vs. SCE) and the decrease of the second (-0.92 V vs. SCE) accompanying the positive shift of the halfwave potentials. (3) The spectral and polarographic behavior with the increase of concentration of sodium perchlorate corresponded to those with the decrease of pH. (4) The flavylium salt (colored form)-carbinol base (colorless form) equilibrium in malvidin-3, 5-diglucoside solution shifted toward the former form when sodium perchlorate was added. (5) These evidences suggested that the hyperchromic effect (enrichment of absorbance at 520nm) of sodium perchlorate on the acidic anthocyanin solutions resulted from the conversion of colorless form into colored form (flavyliums alt).