Interfacial and rheological properties of gelatin based solid emulsions prepared with acid or alkali pretreated gelatins

Abstract

In this study gelled emulsions (10, 20, 40 and 50 wt.% corn oil) and oil-free gels have been prepared using either acid (type A) or alkaline (type B) pre-treated gelatins with varying Bloom values and molecular weights. The gelling kinetics of the gels were monitored by performing small strain oscillatory measurements in combination with a temperature sweep. Increasing setting and melting temperatures as a function of oil content were obtained for the gelled emulsions prepared with type A gelatin. The shear storage moduli for the gels were determined after curing at 20 °C for 15 min and compared to estimated values using a simplified version of the van der Poel's formula. A steeper increase in moduli as a function of oil content was obtained for the gelled emulsions prepared with the acid pretreated gelatins, also overshooting the estimated values. It is suggested that the higher moduli and setting and melting temperatures are caused by a hydrogen bond mediated flocculation of the oil droplets. Measurements of interfacial tension between gelatin solutions and corn oil, indicated that type A gelatin samples were more surface active compared to type B gelatin samples. This was attributed to the assumed presence of minor contaminants in the acid pre-treated gelatin samples, which were able to adsorb and reduce the interfacial tension at a faster rate. Finally, gelled emulsions were prepared using a cold water fish gelatin. It was observed that by the introduction of oil droplets, potentially improved physical properties may be obtained for these gels.