STUDY OF PROTOLITICAL EQUILIBRIUM IN AQUEOUS SOLUTIONS OF MALIC ACID IN ORDER TO ESTIMATE ITS INFLUENCE THE QUALITY OF WINE
Organic acids are the main indicators of the chemical composition of grapes and wine, participate actively in the processes occurring in the wine formation, determine the acidic properties and taste of wines, the stability of products to turbidity, the intensity of redox processes is affected, and they are the markers of the authenticity of wines. The results of study of the behavior of one of the main grapes and wine acids - malic acid are given in the paper. It is characterized by a sharp taste and can be transformed into lactic acid during biological acid reducing of wines. We analyzed the aqueous solutions of malic acid in concentrations from 0.549 103 to 1.792 103 mol / dm3 in the presence of strong electrolytes during continuous potentiometric titration with a coulometrically generated base in order to determine its effect the integral characteristics of wine quality. The titration of solutions was carried out against a background of 1.0 mol / dm3 KCl to maintain the constant ionic strength and conductivity in a setup consisting of a diaphragmless cell with generator and indicator electrodes. It has been hypothesized that in highly diluted solutions, malic acid and its anionic forms are in dimeric form. An analysis of experimental data and its theoretical interpretation show that malic acid is titrated as tetrabasic acid, and its existence in a stable dimeric form is confirmed. The nature of hydrogenic and intermolecular bonds is discussed. Critical points of malic acid solutions were found using the titration curves ( с , pH0, pH1, t1, t2  etc.) whose values can be used for the integral quality control of wines. It is proposed to use the results obtained to improve methods for assessing quality and identifying the grape raw materials and the wines.