Mohammad Anvari

Characterization of fish gelatin–gum arabic complex coacervates as influenced by phase separation temperature

The rheological and structural characteristics of fish gelatin (FG)-gum arabic (GA) complex coacervate phase, separated from an aqueous mixture of 1% FG and 1% GA at pH 3.5, were investigated as influenced by phase separation temperature. Decreasing the phase separation temperature from 40 to 10 °C lead to: (1) the formation of a coacervate phase with a larger volume fraction and higher biopolymer concentrations, which is more viscous, more structural resistant at low shear rates, more shear-thinning at high shear rates, and more condensed in microstructure, (2) a solid-like elastic behavior of the phase separated at 10 °C at a high oscillatory frequency, (3) the increase in gelling and melting temperatures of the coacervate phase (3.7-3.9 °C and 6.2-6.9 °C, respectively), (4) the formation of a more rigid and thermo-stable coacervate gel. The coacervate phase is regarded as a homogeneously networked biopolymer matrix dispersed with water vacuoles and its gel as a weak physical gel reinforced by FG-GA attractive electrostatic interactions.

Effect of cooling-heating rate on sol-gel transformation of fish gelatin-gum arabic complex coacervate phase.

The objective of this study was to characterize influence of different cooling and heating rates on gelation of fish gelatin (FG)-gum arabic (GA) complex coacervate phase using rheological measurements. For the coacervate phase prepared at 10°C, the gelling temperature, melting temperature, gel strength, and stress relaxation decreased with increasing cooling or heating rate, however, no gelation was observed at the highest cooling rate of 0.05°C/min. Similar trends were obtained for the coacervates phase prepared at 30°C, but the gelation did not occur at a cooling rate of 0.033 or 0.05°C/min. The results indicated that rheological properties of FG-GA coacervate gels were highly dependent to the cooling process, where more thermos-stable and stronger gels formed at slower cooling. This was probably because of higher degree of molecular rearrangements, more hydrogen bindings, and formation of greater junction zones into the gel network at slower cooling rates. However, all of the FG-GA coacervate gels obtained at different cooling rates were classified as a weak physical gel.

Effect of fish gelatin-gum arabic interactions on structural and functional properties of concentrated emulsions

Concentrated emulsions containing both proteins and polysaccharides are the basis for many commercial products; however, the effects of protein-polysaccharide interactions on the functional properties of these complex systems are often poorly understood from a fundamental standpoint. Hence, the objective of this study was to determine the effects of fish gelatin (FG)-gum arabic (GA) complexation at different aqueous phase pH (3.6, 5.0, and 9.0) on concentrated emulsion structure-function relationships. Concentrated emulsions were prepared using FG-GA mixtures and characterized by rheometry and confocal scanning laser microscopy (CSLM). CSLM images showed that all samples were O/W emulsions; emulsions with lower pH showed smaller oil droplets, greater homogeneity in size distribution, and higher stability. This was attributed to an increased number of FG-GA complexes in the emulsification. Electrostatic attractive interactions and charge neutralization created biopolymer associations with increased emulsification capacity. Samples with FG-GA mixtures at lower pH showed higher elastic moduli under small deformation and exhibited greater deviation between apparent and complex viscosities under the Cox-Merz rule, indicating increased gel network extension and greater intermolecular connectivity between adsorbed layers of adjacent oil droplets. These results can be used to incorporate protein-polysaccharide complexes as a suitable emulsifier in materials comprising concentrated emulsions.