Acid-induced Aggregation and Gelation of Sodium Caseinate-Guar Gum Mixtures

Abstract

The aim of this work was to study the formation of bovine sodium caseinate (NaCAS) acid gels induced by addition of glucono-delta-lactone (GDL) in the presence of guar gum (GG). At low biopolymer´s concentrations, a one-phase system was observed, whereas at higher mixture concentrations two-phase systems were formed.Aggregation (at low NaCAS concentrations) and gelation (at high NaCAS concentrations) processes were analyzed through the use of full and fractional factorial experiment designs, using turbidimetric and rheological techniques. Finally, the gel images were obtained by confocal laser scanning microscopy and the images were analyzed. Results showed that at low NaCAS concentrations, the presence of GG affects the pH at which aggregation begins but was not significant for the time at which aggregation begins. On the other hand, at high NaCAS concentrations, the concentration of GG only affected significantly the elastic character of acid gels. As polysaccharide concentration increases, the gels obtained were weaker and with larger pores. Also, the formation of NaCAS droplet-shaped structures at certain biopolymer ratio was observed. The presence of GG affects both the rate of gelation and phase separation, which, in turn, determine the type of gel microstructure. Phase separation seems to occur prior to protein gelation because the protein gel network is discontinued, hindering the gel compactness and reducing gel strength. In summary, GG modifies NaCAS stabilization (self-association and phase separation) and the viscoelasticity and microstructure of NaCAS acid gels. The control of such processes and properties would allow obtaining mixture gels with different textures.