Interaction of pectin with amino acids and other amino compounds in aqueous solution

Various foodstuffs and raw materials contain both pectic substances and different nitrogen-containing organic compounds: proteins, peptides, amino acids, alkaloids and many other amino compounds. Various non-enzymatic interactions between pectin and an amino compound in aqueous medium could occur during the processing of these foodstuffs and their storage. Amidation (aminolysis) or hydrolysis of the pectin ester groups, decarboxylation of the free carboxyl groups, beta-elimination or hydrolysis of glycosidic bonds are among the theoretically expected reactions of pectin. Their identification and extent has been studied on model reactions. The results on the interaction between pectin and lysine, methyl glycine, guanidine and some amines in water at 18, 40, 85 and 90 degreesC are presented. All above-mentioned reactions were observed under the conditions investigated and with all amino compounds studied, but the rates of the reactions varied widely. beta-Elimination proceeded very slowly even at high temperature, while amidation, hydrolysis of ester groups (saponification) or of glycosidic bonds (pectin degradation) and decarboxylation of the free carboxyl groups took place at measurable rates. Amidation was more pronounced in the case of lysine, glycine methyl ester, methylamine and diaminoethane, while hydrolysis of ester groups of pectin was more prominent with guanidine as well as with primary amines. Decarboxylation took place at a slow rate in all examined cases (from 3 to 11%). Indexes degree of hydrolysis of pectin ester groups and degree of decarboxylation of pectin are introduced. The results indicate that it should be studied whether or not similar processes possibly occur during the thermal treatment of pectin- and protein-rich plant raw materials. (C) 2003 Elsevier Ltd. All rights reserved.