Effect of Xanthan Gum on the Rheological Behavior and Microstructure of Sodium Caseinate Acid Gels.

María Hidalgo,Mirta Armendariz,Patricia Risso,Jorge Wagner

doi:10.3390/gels2030023

Abstract

The aim of this work was to study the effect of xanthan gum (XG) on the gelation process of bovine sodium caseinate (NaCAS) induced by acidification with glucono-δ-lactone (GDL) and on the mixed acid gel microstructure. Before GDL addition, segregative phase separation was observed in all the NaCAS-XG mixtures evaluated. The gelation process was analyzed by using a fractional factorial experimental design. The images of the microstructure of the mixed acid gels were obtained by conventional optical microscopy and the mean diameter of the interstices was determined. Both the elastic character and the microstructure of the gels depended on the concentrations of XG added. As XG concentration increased, the kinetics of the gelation process was modified and the degree of compactness and elasticity component of the gel network increased. The microstructure of gels depends on the balance among thermodynamic incompatibility, protein gelation and NaCAS-XG interactions.

Highlights

Mixed gels of proteins and polysaccharides have proved to control the texture and stability of food products
The isoelectric point of NaCAS, the addition of xanthan gum (XG) leads to a segregative phase separation throughout the range of the concentrations assayed
The presence of the polysaccharide leads to NaCAS conformational changes related to a higher exposition of the protein intrinsic fluorophores to a polar environment as the CXG

Summary

Introduction

Mixed gels of proteins and polysaccharides have proved to control the texture and stability of food products. It is essential to understand the interactions between both biopolymers and how they contribute to the improvement of the physical properties of food [1,2]. The mixture of proteins and polysaccharides in aqueous solutions can result in phase separation, which can be either segregative due to limited thermodynamic compatibility, or associative due to the formation of a complex through weak and nonspecific interactions [2]. Thermodynamic incompatibility, which arises from the low entropy of mixing two polymers, usually occurs near the protein isoelectric point, promoting protein self-association and/or when each polymer has a different affinity for the solvent [3]. The acidification of NaCAS generates gel formation near the isoelectric point (pI). The physical properties of NaCAS gels are intimately associated with their chemical properties [4] and with different factors such as pH, temperature and ionic strength [5,6,7]

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