Design and characterization of double-cross-linked emulsion gels using mixed biopolymers: Zein and sodium alginate

In this study, a double-cross-linked emulsion gel was formed using a Pickering emulsion as a template and two food-grade biopolymers, zein and sodium alginate (SA), as gelling agents. First, the zein was crosslinked with transglutaminase (TG) and then the alginate was crosslinked with calcium ions. The structure, interactions, and functional properties of the composite systems were then characterized using microscopy, infrared spectroscopy, and rheology measurements. These methods provided valuable insights into the formation mechanism of the double-cross-linked emulsion gels. The effects of single/double cross-linked emulsion gels on the photostability and bioaccessibility of co-loaded polyphenols (curcumin and resveratrol) were also compared. Our results show that SA concentration and TG activity impact emulsion gels stability and rheology. Single-cross-linked emulsion gels could be formed by only crosslinking SA (0.5 wt%) with calcium ions, but not by only crosslinking zein with TG. Double-cross-linked emulsion gels with dense network microstructures and high viscoelasticity were formed by using 60 U/g TG and 1.25 mM Ca2+ to crosslink the protein and polysaccharide, respectively. The single cross-linked emulsion gels improved the light stability and bioaccessibility of the two polyphenols, with the Ca2+-crosslinked system being more effective than the TG-crosslinked one. The double-cross-linked emulsion gels gave higher light stability and bioaccessibility than the single-cross-linked ones. Overall, this study shows that using a combination of TG and Ca2+ to crosslink the two biopolymers leads to edible composite materials with improved functional performance.