D-アラポアスコルビン酸存在下におけるL-アスコルビン酸の分解について(第3報)開放条件下における検討

抄録

Decomposition of L-ascorbic acid with and without D-araboascorbic acid in the aqueous solution was studied in atmospheric condition. Experiments were carried out using cylindrical glass vessels. At each pH, the logarithm of the residual percentage of L-ascorbic acid was found to have a rectilinear correlation with time, and the decomposition rate constant of L-ascorbic acid decreased with increase in the concentration of L-ascorbic acid. Even on varying the liquid height of L-ascorbic acid solution in the same diameter vessels, a rectilinear correlation was also observed between both logarithms of the liquid heights and of the rate constants of L-ascorbic acid in the pH range from 2.4 to 6.0. By extrapolation of the regression lines, the pH-rate profile at the liquid height of 1 mm was obtained. From kinetical studies, it was also found that a complex between undissated form and monohydrogen ascorbate play some role in a series of decomposition processed under the atmospheric condition as well as under the anaerobic condition. In the case of the same initial concentration of L-ascorbic acid and D-araboascorbic acid, a considerable difference was not recognized between the rate constants of the decomposition of L-ascobic acid and of D-araboascobic acid, respectively. Further, it was recognized that the rate constant of L-ascorbic acid (or D-araboascorbic acid) in the mixture of L-ascorbic acid and D-araboascorbic acid is approximately equal to the rate constant of L-ascorbic acid at the same concentration to the total concentration of both acids. Thus, L-ascorbic acid was stabilized in the presence of D-araboascorbic acid. It can be reasonably concluded that observed stability increase of L-ascorbic acid dose not depend on the anti-oxidizing effect (the preferably oxidized) by D-araboascorpic acid, but is merely based on the effect by the increase of the total concentration of both acids.