Effect of the structural features of pectins and alginates on their thermodynamic compatibility with gelatin in aqueous media

Thermodynamic compatibility and phase equilibria were studied in aqueous systems containing gelatin with pectin or with sodium alginate. Pectins with various degrees of esterification, block and statistical distribution of free carboxyl and ester groups as well as alginates of various block-structures were used. lt was found that at high ionic strength (mu) of greater than or similar to 0.2 the systems studied separated into two phases. The compatibility of macromolecular components was increased with an increase in esterification degree of pectin, local concentration of its ester groups and with a decrease in temperature and pH. An increase in the content of mixed MG-blocks in alginates increased their compatibility with gelatin. At low mu (<0.15) and pH above isoelectric point of the protein the above systems exhibit a single-phase behavior. It is suggested that the dominant mechanism controlling compatibility of gelatin with anionic polysaccharides involves the creation of weakly bound complexes of various origins, which destruct at increased salt concentrations and temperatures.