Structural modification of zein-based oil-in-glycerol emulsion gels for improved textural and digestion behaviors

Zein can dissolve in glycerol, and can be developed into oil-in-glycerol emulsion gels to widen its applications. The current study focused on modulating the structures of zein-based emulsion gels by the addition of a surface active ingredient (Span 20, SP) to improve textural and digestion behaviors. Microstructural observation indicated that the addition of SP replaced zein from the oil-glycerol interface, and allowed a higher level of oil droplet aggregation. After adding SP, the gel hardness decreased from 3.43 +/- 0.14 N to 1.62 +/- 0.01 N, and the storage modulus also decreased with the increase of SP content. Viscoelasticity of the gels was thermo-responsive, and the presence of SP contributed to a higher recovery of the storage modulus after the heating-cooling process. The addition of SP reduced the oil-binding capacity of zein gel from 97.61 +/- 0.19% to 82.00 +/- 0.92% and the solvent-binding capacity from 75.97 +/- 3.05% to 62.25 +/- 0.22%, indicating that the zein network was weakened. Then, gels were mixed with simulated digestive juices to track the changes of gel structures and the release of free fatty acids. The addition of SP accelerated the digestion process, especially intestinal digestion. SP contributed to a higher fluorescence intensity in the digesta, which was a sign of a higher level of digestion of zein. Subsequently, the addition of SP increased the release content of free fatty acids from 4.27 +/- 0.71% to 5.07 +/- 1.27%. The above findings would be useful in designing zein-based functional food products with favored textural and digestion properties.