Influence of chickpea protein on the pH and temperature dependent viscosity of carboxymethylated starch

Proteins can significantly improve the elasticity and microstructure of starch gels in food. In this work, the influence of chickpea protein flour on the viscoelastic behaviour of carboxymethylated starch (CMS, 92.6 mmol COOH kg(-1)) gels was studied as function of pH and temperature. A weight ratio CMS:protein flour of 1:0.45 was investigated in the pH range of pH 2.5-8. Above pH 7 presence of 7.5 %w/w chickpea flour lead to an increase in complex viscosity of a 16.5 %w/w CMS solution by a factor of 10. The interaction between CMS and protein above pH 4 accelerates gelation at 37 degrees C, resulting in an increase in viscosity by a factor of 5, 10 and 120 at pH 5, pH 7 and pH 8 respectively. Model calculations for species dissociation of ammonium groups in basic amino acids and carboxylate groups in CMS indicate that electrostatic interactions led to the observed increase in viscosity. The results form a general model to explain the pH-dependent viscoelastic behaviour of polysaccharide-protein mixtures. The understanding of the mechanism of action between protein and polysaccharides is a condition for targeted analysis and explanation of many phenomena of texture, stability and coacervate formation in food processing.