Effect of starch type on the physicochemical and emulsifying properties of amorphous starch-whey protein isolate mixtures

Starch from several plant sources, namely Japonica rice starch (JRS), waxy rice starch (WRS), corn starch (CS), wheat starch (WS), pea starch (PeS), potato starch (PtS), and tapioca starch (TS), were separately pasted into amorphous mixtures with whey protein isolate (WPI). The physicochemical and emulsifying properties of the seven amorphous starch-WPI mixtures were characterized. Each starch-WPI mixture showed a lower fluorescence intensity than that of WPI alone. The mixtures containing PtS, PeS, CS, and WS, which have higher amylose content, had lower fluorescence intensities than the other mixtures. The PeS-, CS-, and WS-WPI mixtures had lower zeta-potentials and larger particle sizes, contained remnants of starch granules, and exhibited a low paste viscosity. The droplet sizes of emulsions stabilized with the amorphous starch-WPI mixtures ranged from 2.82 to 7.04 & mu;m. The emulsions stabilized with either PtS-, PeS-, CS-, or WS-WPI mixtures had smaller droplet sizes and higher storage modulus (G & PRIME;) values and showed no creaming after storage for 30 d, whereas severe creaming occurred in the emulsions containing WRS-, TS-, or JRS-WPI mixtures. Microscopic imaging revealed that the mixtures-stabilized emulsions were composed of WPI-adsorbed spherical droplets with starch in the continuous phase.