Role of interfacial compositions in achieving dispersed phase-induced gelation and controlled digestion of oil-in-water bilayer nanoemulsions

Abstract

Conventional emulsion gels with sub-micrometre droplet size are part of many foods where the disperse-phase induced gelation can be achieved at higher oil volume fraction (f) through random jamming. Interestingly, random jamming can also be induced at a lower f by reducing the droplet size (r) to nanoscale and increasing the interfacial shell-layer thickness (d). Specifically, interfacial compositions can play a significant role in elevating d, when reduction in r becomes a limiting factor. In this study, two different interfacial compositions (low molecular weight emulsifier (Citrem) or whey protein isolate (WPI)) were used to prepare the single-layer 40wt% O/W nanoemulsions (r ~ 200 nm) using high-pressure homogenization. To increase the d, the second layer of polysaccharide (chitosan or pectin) was deposited on single-layer-stabilized nanodroplets using the layer-by-layer (LbL) electrostatic deposition technique. Deposition of chitosan transformed a liquid Citrem-stabilized single-layer emulsion into repulsive bilayer weak emulsions gel, indicated by 15 times increase in storage modulus (G¢). Oppositely, deposition of pectin second layer on WPI-stabilized nanodroplets showed a much stronger elastic bilayer gel. A self-standing viscoelastic gel obtained for the WPI-pectin bilayer nanoemulsions could be attributed to the close-packed structure (random jamming) of nanodroplets compared to the lack of that in Citrem-chitosan-stabilized bilayer nanoemulsions at similar f (0.36). The electrostatic and steric repulsive forces (from the WPI and pectin) significantly contributed to achieving the dispersed phase-induced gelation by elevating d and effective oil volume fraction (feff) of nanodroplets. The deposition of the second layer, chitosan and pectin, on nanodroplets also led to 32% and 57% reduction of in vitro lipid digestibility, respectively, compared to single-layer nanoemulsions. Overall, this study showed that the dispersed-phase induced gelation (at a lower oil content) and controlled digestion in nanoemulsions can be achieved by manipulating the interfacial compositions.