Phase separation and gel formation in kinetically trapped gelatin/maltodextrin gels

Abstract

The kinetics of phase separation and gel formation of gelatin/maltodextrin mixtures have been studied using confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), stereological image analysis and rheology. The quantified microstructural parameters were the volume-weighted mean volume and the interfacial area. The temperature of phase separation was defined as the temperature where the first signs of phase separation were observed in CLSM. The gelatin concentration varied between 4 (wt.) and 5% and the maltodextrin concentration varied between 2 and 6%. Maltodextrin was labelled covalently with RITC to improve the contrast between the gelatin phase and the maltodextrin phase. The solutions were cooled from 60 to 10°C, and the cooling rates used were 0.4, 1 and 3°C/min. All systems were found to be gelatin continuous under the experimental conditions used. The results showed that the temperature of phase separation ( T PS) increased both with the gelatin concentration and the maltodextrin concentration, but particularly with the former. The size of the maltodextrin inclusions increased with T PS, and the interfacial area decreased with increasing T PS. The diameter of the maltodextrin inclusions varied between 1.6 and 8.5 μm at 1°C/min. The size of the maltodextrin inclusions was found to increase with decreasing cooling rate and was largest at 0.4°C/min. The T PS was compared with the gelation temperature ( T gel) at three different concentrations of gelatin and maltodextrin (4/3, 4/5, 5/5%). CLSM micrographs and TEM micrographs showed that these three concentrations of gelatin and maltodextrin had different microstructures. At a T PS above T gel (5/5%), the phase separation proceeded faster than the gel formation and the microstructure had few, large maltodextrin inclusions and a clean continuous gelatin phase. At a T PS comparable with T gel (4/5%), phase separation occurred during gel formation, which led to a varying microstructure and competition between the phase separation and the gel formation. At a T PS below T gel (4/3%), gel formation proceeded faster than the phase separation and the microstructure had many, small inclusions and a diffuse microstructure, and the phase separation was incomplete. It was established that the microstructure was determined by the relative rates of the phase separation and the gel formation. Three different zones of phase separation could be distinguished based on comparisons of T PS and T gel, and results from CLSM, TEM and image analysis.