Effects of degree of deacetylation and concentration of chitosan on the rheology and functional properties of Citrem-chitosan-stabilized bilayer nanoemulsions

Supratim Ghosh

University of Saskatchewan

In emulsion gels, flow behaviour could be restricted due to repulsive jamming or attractive droplet aggregation. For nanoemulsions, repulsive jamming could be induced by decreasing droplet size and increasing interfacial shell-layer thickness. In this work positively charged chitosan with different degree of deacetylation (DDA 50 and 93%) was used to form bilayer electrostatic deposition on negatively charged Citrem (citric acid esters of monoglycerides)-stabilized oil droplets with the aim to determine the influence of interfacial shell-layer on repulsive gelation. The primary Citrem-stabilized liquid nanoemulsions (d₃₂<200 nm) were prepared by high-pressure homogenization. After removal of excess Citrem by multiple centrifugations, secondary nanoemulsions were fabricated by adding different concentrations (0-0.25wt%) of chitosan at pH 4. With an increase in DDA93 chitosan concentration, negative charge (-48.0mV) of primary emulsion decreased to zero at 0.075wt%, increased to +51.9mV at 0.2wt% and remained unchanged thereafter. However, DDA50 chitosan showed a lower magnitude of positive charge and reached a maximum of +40.1mV at 0.2wt%. Accordingly, the microstructure changed from free-flowing Citrem-stabilized nanodroplets to aggregated droplets at ≤0.15wt%, and uniformly coated droplets at ≥0.2wt% chitosan. Emulsion viscoelasticity also went through a maximum which could be attributed to weak gels without chitosan, followed by strong aggregated gels between 0.05-0.15wt% chitosan, and smooth gels beyond 0.2wt% chitosan. With DDA50, viscoelastic maxima shifted towards a higher concentration of chitosan. Lipid digestibility of all bilayer nanoemulsions was decreased significantly compared to the primary nanoemulsion. Such gelation in bilayer nanoemulsions using a combined electrostatic and steric repulsion can serve as an attractive option to produce low-fat products.