Complexes of Porcine Gelatin with Carrageenans: Influence of pH, Presence of Salts, and Polysaccharide Type

The effect of the polysaccharide:protein mass ratio, pH, concentration, and nature of the inorganic salt (sodium and calcium chlorides) on the phase behavior of aqueous mixtures of porcine gelatin with kappa-, lambda-, or iota-carrageenans was studied using turbidimetric titration. The formation of insoluble protein-polysaccharide complexes was observed in the range of pH between two boundary values, which decreased with increasing polysaccharide–protein mass ratio (Z). An increase in the number of sulfate groups in the polysaccharide in the series kappa- < iota- < lambda-carrageenan leads to a decrease in the boundary pH values at constant Z. Electrostatic interactions between gelatin and carrageenan molecules are suppressed with increasing ionic strength, which leads to the destruction of insoluble complexes upon addition of salts.