Structure of gels produced from sodium caseinate

CRISTIÁN HUCK IRIART; MARÍA SOLEDAD ÁLVAREZ CERIMEDO; ROBERTO J. CANDAL; MARIA LIDIA HERRERA

Otro; proyecto realizado en LNLS; 2009

X-ray diffraction analysis at small angles was proposed as a nondestructive method for characterization of emulsions (1). Most dispersed multiphase systems are thermodynam- ically unstable per se and thus require stabilization. In the food industry, actually stabilization of emulsions is obtained by the addition of proteins such as sodium caseinate (NaCas). The addition of this protein has a double stabilizing effect since it provokes together with other added surfactants an in- crease of both viscosity of the continuous phase and stabil- ity of the interface. Physical instability results in an alter- ation in the spatial distribution or structural organization of the molecules. Creaming, flocculation, coalescence, partial coalescence, phase inversion, and Ostwald ripening are exam- ples of physical instability. The development of an effective strategy to prevent undesirable changes in the properties of a particular food emulsion depends on the dominant physico- chemical mechanism(s) responsible for the changes. In prac- tice, two or more of these mechanisms may operate in con- cert. It is therefore important for food scientists to identify the relative importance of each mechanism, the relationship between them, and the factors that influence them, so that ef- fective means of controlling the stability and physicochemi- cal properties of emulsions can be established (2). Previous studies in our laboratory showed that the main mechanism of destabilization in a given formulation depended on NaCas concentration and particle size distribution. Emulsions with mean diameter in volume (D4,3) around 0.5 micrometers and formulated with 0.5 and 1 w in w NaCas destabilized mainly by creaming of small particles. For the 2 w in w NaCas emul- sion, both mechanisms, creaming and flocculation, were in- volved. Migration of small particles occurred during the first 24 h and then bigger particles formed by aggregation moved up. For the 3, 4, and 5 w in w NaCas the main mechanism was flocculation. Confocal images of these samples showed that the spatial distribution of droplets was markedly different for both, creaming and flocculation processes. The images obtained when the 20 w in w trehalose/10 w in w CFO emul- sions stabilized with different amounts of NaCas were kept at 22.5 C for 24 h are shown in Figure 1. The images corre- sponding to emulsions stabilized with 0.5 or 1 w in w NaCas showed a homogeneous droplet distribution. Differences in both images are in agreement with the decrease in D4,3 with NaCas concentration. A dye was dissolved in the fat phase which appeared in red. When protein concentration was 2, 3 or 4 w in w emulsions presented aggregates/flocculates which were absent in 0.5 and 1 w in w emulsions. In these emul- sions there were more protein for the coverage of oil dropletsurface and higher protein concentration in the aqueous phase. Surprisingly, a concentration of 5 wtThe structural dissimilari- ties among emulsions could result in differences in SAXS pat- terns. Therefore, the aim of the present work was to describe the structure of emulsions formulated with different concen- trations of NaCas as stabilizer. The effect of fat phase type and sugar type and concentration were also examined.