Metatartaric acid esterification number

The esterification number of different metatartaric acid preparations may be determined by acidimetric assay, before and after saponification. Table 1.18 shows the importance of the preparation conditions in determining this value. 

Metatartaric acid is by no means a pure product solutions are slightly colored and oxidizable. They may contain oxaloacetic acid, but the main impurity is pyruvic acid, representing 1-6% by weight of the metatartaric acid, according to the preparation conditions (Table 1.18). It is, therefore, important to correct the esterification number to compensate for this impurity. The formation of... 

There are many laboratory tests for assessing the effectiveness of a metatartaric acid preparation. Table 1.19 presents an example of a procedure where a saturated potassium bitartrate solution is placed in 10 ml test tubes and increasing quantities of metatartaric acid preparations with different esterification numbers are added. This inhibits the precipitation of potassium bitartrate induced by adding 1 ml EtOH at 96% vol and leaving the preparation overnight at 0°C. Only 1.6 mg of a preparation with an esterification number of 10 is... 

The fact that metatartaric acid solutions are unstable has a major impact on their use in winemaking. They deteriorate fairly rapidly and are also sensitive to temperature. Hydrolysis of the ester functions occurs, accompanied by an increase in acidity. After 20 days at 18-20°C, there is a considerable decrease in the esterification number (Figure 1.20). Under experimental conditions, total hydrolysis of a 2% metatartaric acid solution took three months at 23°C and 10 months at 5°C. Consequently, it is necessary to ensure that metatartaric acid solutions for treating wine are prepared just prior to use. 

Number Esterification number Metatartaric acid added in each tube (in mg) ... 

Fig. 1.20. Hydrolysis rate of two qualities of metatartaric acid in 2% solution (f in the esterification number (Ribdreau-Gayon et al., 1977)...

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