Abstract
The purpose of this study was to examine the impact of mixing methods, emulsifier types and molecular weights of barley β-glucan (BG) on emulsification and in vitro lipolysis of canola oil-in-water emulsions. Three different emulsifiers, Triton x100 (TTN), lecithin (LCN) and whey protein isolate (WPI), and three orders of mixing high molecular weight barley BG with oil and emulsifier were studied by measuring viscosity, microstructure and particle size distribution of the systems; while extent of lipolysis was quantified by an in vitro digestion method. In addition, lipids initially emulsified with TTN were mixed with barley BG of low, medium and high molecular weight to determine the effect of BG molecular weight on canola oil emulsion structure and lipolysis. In the absence of barley BG, lipid emulsification depended on the emulsifier type with larger lipid droplets found in WPI stabilized emulsions. Incubating emulsions with fibres increased the viscosity and size of the emulsified droplets, but to different extents depending on the emulsifier type and mixing order. Addition of BG reduced lipid digestion to the greatest extent for initially small droplet sizes, but independent of viscosity. Microstructure and particle size analysis suggest that the mechanism involves droplet flocculation restricting the surface area available for lipase action. Changes in droplet size distribution were observed after digestion only for high molecular weight BG, with more large droplets. All BG samples slowed lipolysis of emulsions but to different extents depending on the molecular weight with the largest BG significantly reducing lipolysis (p < 0.05). A rationalization is proposed for the impact of different molecular weights of barley BG on the depletion flocculation of emulsions using two models. These results enhance our understanding of the impact of soluble dietary fibres on the physicochemical and structural changes that may occur to emulsified lipids within the gastrointestinal tract.
