Application of Water-Pyridine Solvent System for Electrochemical Measurement of Organic Acid Content

Study on Sourness of Food and its Electrochemical Measurement (part IV)

Abstract

The electrochemical method developed for measuring organic acid contents in foods was applied to the water-pyridine solvent system. If the concentration of pyridine was below 20% (v/v), plots of organic acid content vs. measured conductance gave straight line. This fact agreed with the theory of the analytical method. By studying the conductance of strong electrolyte and that of organic acid in solvent mixtures, it was found that 10% (v/v) pyridine was best for analysis. Concentration of hydrogen ion measured by this improved method corresponds to all of the possible hydrogen ion measured by alkalimetry. All of the major organic acids observed in foods gave better linear plots in water-pyridine solvent system than in water. The slopes of linear line was dependent on the basicity and the ionic equivalent conductance of anion. The slops obtained in three organic acids; tartaric acid, malic acid and succinic acid were almost equal. In application of this improved method to the commercial beverage containing citrus juice, high precision was obtained.