Whey protein–maltodextrin conjugates as emulsifying agents: An alternative to gum arabic

The emulsifying properties of covalent complexes of maltodextrin (MD) with whey protein (WP) isolate have been investigated under both acidic and high electrolyte concentration conditions in systems containing medium-chain triglyceride oil or orange oil. Covalent coupling of protein to polysaccharide was achieved by dry-heat treatment of a protein+polysaccharide mixture for up to 2 h. It was confirmed by SDS-polyacrylamide gel electrophoresis that the WP does become directly linked to the MD. Analysis of droplet-size distributions has shown that this covalent linking of MD to WP leads to a very substantial enhancement in the protein emulsifying behaviour under both acidic and neutral conditions. Analogous dry-heating treatment of MD with soy protein does not have this positive effect. A whey protein–MD conjugate WP–MD19, made from MD (DE=19) of intermediate mean molecular weight (8.7 kDa), has been found to be capable of producing fine emulsion droplets (0.5–1 μm) with either triglyceride oil or orange oil. Optimized WP–MD19 conjugates can produce fine stable emulsions (20 vol% oil) at 2 wt% emulsifier content, whereas the equivalent emulsion made with gum arabic requires a 20–30 wt% level of emulsifier. A WP–MD19 conjugate of protein/polysaccharide ratio 1:2 or 1:3 is effective in stabilizing low-pH emulsions of a commercial flavour oil (containing a weighting agent) over a storage period of several weeks, with no visible precipitation or phase separation when mixed with colouring agents, either before or after extensive emulsion dilution.