Comparision of heteroaggregation, layer-by-layer and directly mixing techniques on the physical properties and in vitro digestion of emulsions

Abstract This paper systematically compared the effects of heteroaggregation, layer-by-layer and directly mixing techniques on the physical properties of emulsions through mechanical rheology, microrheology, LUMisizer stability analyzer, Cryo-scanning electron microscopy (Cryo-SEM) and in vitro simulated gastrointestinal model. The shear rheology results showed that the viscosity of emulsions stabilized with whey protein isolate (WPI) and flaxseed gum (FG) by different techniques was in the order of heteroaggregated emulsion > layer-by-layer emulsion > directly mixing emulsion. Furthermore, it confirmed that the heteroaggregated emulsion had a best stability and the interface moving speed was the slowest compared with those of layer-by-layer and directly mixing emulsions. Cryo-SEM microstructure results showed that the three dimensional network structure of heteroaggregate was the main reason for maintaining high stability and shear rheological properties. Microrheological properties results indicated that heteroaggregated emulsion was sensitive to the shearing force due to the liquid behavior. While, the structures of WPI-FG emulsions prepared by layer-by-layer and directly mixing were not destroyed after shearing due to their high elasticity and solid behaviors. It was found that the order of released FFA content at the beginning of 30 min was directly mixing emulsion > layer-by-layer emulsion > heteroaggregated emulsion, but the released free fatty acid of heteroaggregated emulsion was the most in the end, which indicated that heteroaggregated emulsion had a certain controlled release effect. The study could be helpful for choosing proper technique to gain good emulsion delivery system.