Microstructure determined the gel properties of gelatin/dextran more than the macrophase separation

Hydrogels are important in foods. Although the hydrogel microstructure has been commonly reported, the effect of the microstructure before and after gelation on gel properties was rarely investigated. This work aims to explore the effects of micro- and macro-phase separation of type-A gelatin-dextran (GEA/DE) aqueous solutions on the rheological, texture, and hydration properties of GEA/DE hydrogels. Three types of phase separation microstructures at both pH 5.0 and 7.0, e.g., DE-in-GEA emulsion, bicontinuous microstructure, and GEA-in-DE emulsion, were designed by adding different DE concentrations. GEA/DE mixtures showed macro-stability at pH 5.0, but macroscopic phase separation at pH 7.0, in which the phase separation time increased with the increasing DE concentration. During cooling-gelation, microstructures of mixtures were almost unchanged at pH 5.0, but significantly changed at pH 7.0. Interestingly, the microstructure determined the gel properties of phase-separated gels more than the macrophase separation. Microstructures of continuous phase with the gelling ability, e.g., DE-in-GEA and bicontinuous phase, hardly changed the moduli (G′ and G″) and hardness of GEA/DE mixed gels, while the microstructure of GEA-in-DE without the gelling ability for continuous phase greatly reduced the moduli and hardness. This might be due to the different GEA volume fractions in GEA/DE mixed gels with different microstructures, and the mixed gel strength decreased with decreasing GEA volume fractions. Water holding capacity and swelling ratio of GEA/DE mixed gels reduced with the increasing DE concentration. This work provides some new information on how microstructure and macro-stability affect the physical properties of mixed gels.