Molecular weight characteristics and sorption properties of pectin extracted from different substrates

Abstract

The study of natural polymers is one of the most advanced tasks of modern chemistry. One of these polymers is the common polysaccharide pectin. Widespread acid hydrolysis was used to extract pectin from various substrates. Oxalic, citric and hydrochloric acids have been investigated for this purpose. The water-soluble pectin-containing fraction was extracted from the apples, sugar beet, lemon peel, pine needles. The optimal condition is heating the substrate in a boiling water bath for 1 hour with reflux in a solution of hydrochloric acid (pH 2-3). We neutralized the extract after cooling with an ammonia solution to isolate the dry powder of the pectin-containing component and the pectin was precipitated with ethanol. The study of pectin solutions by the method of gel permeation chromatography showed that they most often have three polymer fractions that are close in molecular weights: ~17-20, ~10-12 and ~0.5 kDa. The content of the last fraction in all selected samples is predominant. Solutions of pre-planted powders of the pectin-containing fraction significantly differ from the previously discussed results: the oligomeric fraction is practically absent in them. For a number of samples of pectin powders, the degree of esterification was determined by potentiometric titration. The dependence of the degree of esterification on both the feedstock and the isolation method was revealed. The method of reverse complexometric titration was used to study the sorption capacity of pectin. The analysis results suggest that there is an inversely proportional dependence of the degree of lead sorption of the pectin sample on its degree of esterification.