抄録
Fruit juice contains many important organic acids which affect the taste of the juice. To control the organic acid composition by nanofiltration, the mechanism of the organic acid separation should be clarified. Nanofiltration experiments were carried out by varying the pH from 2.2 to 8.5 by adding NaOH for the single- and 2-component solutions of citric and ascorbic acid. The membrane and module used in the experiment were a NF-45 membrane and a DDS flat sheet laboratory-scale module. The concentrations of the feed and permeate samples were measured by high-performance liquid chromatography. When the pH increased from 2.2 to 8.5 for the single-component system, the rejection of citric acid increased from 0.36 to 0.98, and the rejection of ascorbic acid increased from 0.25 to 0.81. Assuming that the amount of the rejected organic acid was the sum of the rejected fractions of the ionized and non-ionized organic acids and determining the rejections of both the ionized and non-ionized acids by a curve fitting method, the pH dependence of the calculated total rejection was in good agreement with the experimental results. The rejection of citric acid for the 2-component system became greater only at a lower pH compared to that for the single component system, and the rejection of ascorbic acid for the 2-component system became greater only at a higher pH. These results can be explained by considering that the rejection of the non-ionized citric acid and the ionized ascorbic acid in the 2-component system became greater than that in the single-component system.
