Influence of complexing carboxymethylcellulose on the thermostability and gelation of α-lactalbumin and β-lacto globulin

Thermostability and gelation of the main proteins of whey, a-lactalbumin (alpha-lac) and beta-lactoglobulin (beta-1g) recovered by selective complexation with carboxymethylcellulose (CMC) was studied to evaluate its functionality in food systems. Their behavior was compared to the non-complexed proteins. Both complexes showed a maximum stability at pH 4, that is close to the pH of obtention of 1g/CMC coacervate (pH 4) and alpha-lac/CMC coacervate (pH 3.2). Protein complexation increased the thermostability of alpha-Ig by approximately 6-8 degrees C and that of a-lac by approximately 26 degrees C due to immobilization of protein molecules in a complex, mainly by electrostatic interactions and because of different amounts of bound polysaccharide. The denaturation enthalpy of complexed proteins markedly decreased as compared to free proteins. Storage modulus (G') and loss modulus (G') were recorded to reflect the structure development during heating beta-1g/CMC and alpha-lac/CMC complexes at different pH values. beta-1g/CMC complex at 20 wt% was a viscoelastic liquid at pH values within 2 and 8 but upon heating turned to a particulate viscoelastic gel. However, alpha-lac/CMC complex formed before heating opaque, large visible white particulate aggregates that sticked together to give a solid viscoelastic structure that was not further modified by thermal processing. (C) 2006 Elsevier Ltd. All rights reserved.