IMPROVEMENT OF THE SELECTIVE DEPOLYMERIZATION OF PECTIC SUBSTANCES BY CHEMICAL BETA-ELIMINATION IN AQUEOUS-SOLUTION

The reaction of beta-elimination which splits specifically the glycosidic linkages next to methoxylated galacturonic acid units without steric limitation may be used for the determination of the sequence of methyl esters along pectin molecules. However, due to competitive de-esterification, completeness of the reaction has never been achieved. In order to improve the extent of degradation, the influence of temperature, pH and buffer concentration on the beta-elimination reaction in aqueous solutions has been investigated. Examination of kinetics revealed that any increase of temperature increases the rate of the beta-elimination reaction more than that of the de-estefification. On the other hand, any decrease of pH decreases the rate of beta-elimination but. much less than the rate of de-esterification. Buffer concentration plays an important role by controlling the pH through its buffering capacity as well as the availability of hydroxyl ions. Increasing the temperature up to 115-degrees-C and decreasing the pH down to 5.0 improved the splitting of the glycosidic bonds of a high methoxyl pectin backbone from 5.5 to 38% (53% of the glycosidic bonds contiguous to a methoxylated galacturonide unit). In spite of the appearance of various secondary reaction products, the absorbance at 235 nm can be used to estimate the extent of degradation.