Degradation of Ascorbic Acid in Ethanolic Solutions
Date Issued
2010
Date
2010
Author(s)
Tsai, Yi-Chin
Abstract
For understanding the effect of ethanol on ascorbic acid degradation, 0 - 40 % ethanol concentrations model solution was used. Results from kinetic study showed that the degradation rate constant of ascorbic acid is increased with the increase of ethanol concentration and the degradation of ascorbic acid in ethanolic solutions followed first-order reaction. At 45℃ incubation temperature, the activation energies (Ea) of the ascorbic acid degradation products in 0-40 % ethanolic solutions are between 9.71-3.33 (kcal/mole) with a dose manner. 2-furoic acid and 3-hydroxy-2-pyrone were the major degradation products in ascorbic acid ethanolic model solutions. The production of the two compounds decreased with the increase of ethanol concentrations. According to the above results, we postulate that the aerobic degradation pathway dominates over the anaerobic pathway for ascorbic acid in ethanolic model solutions.
Water activity (aw) and pH value were main factors affecting the ascorbic acid degradation. The results revealed that degradation rate of ascorbic acid in pH 2.6 buffered ethanolic solutions were much faster than in the ethanolic solutions without pH controlling. The formation of degradation products and the browning index of ascorbic acid in pH 2.6 buffered ethanolic solutions were similar to that in the ethanolic model solutions without pH controlling, too. We propose that pH is not the sole factor affecting the ascorbic acid degradation rate in high ethanol concentration solutions. In pH 4.6 buffered ethanolic solutions, the degradation of ascorbic acid, the formation of the degradation products and the browning of the solutions also increased with the increase of ethanol concentration.
Glycerol was used for adjusting to the similar aw of ascorbic acid ethanolic model solutions. The solutions were buffered at pH 2.6 and stored at 45℃. The result shows that degradation rate of ascorbic acid is much faster in buffered glycerol model solutions with higher aw than that in ethanolic model solutions. We postulate that water activity is not the major factor affecting the ascorbic acid degradation in high ethanol concentration solutions.
Subjects
Ascorbic acid
degradation
kinetic
ethanol
browning
Type
thesis
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