Joint Effects of Granule Size and Degree of Substitution on Octenylsuccinated Sweet Potato Starch Granules As Pickering Emulsion Stabilizers

The granules of sweet potato starch were size fractionated into three portions with significantly different median diameters (D50) of 6.67 (small-sized), 11.54 (medium-sized), and 16.96 μm (large-sized), respectively. Each portion was hydrophobized at the mass-based degrees of substitution (DSm) of approximately 0.0095 (low), 0.0160 (medium), and 0.0230 (high). The Pickering emulsion-stabilizing capacities of modified granules were tested, and the resultant emulsions were characterized. The joint effects of granule size and DSm on emulsifying capacity (EC) were investigated by response surface methodology. For small-, medium-, and large-sized fractions, their highest emulsifying capacities are comparable but, respectively, encountered at high (0.0225), medium (0.0158), and low (0.0095) DSm levels. The emulsion droplet size increased with granule size, and the number of freely scattered granules in emulsions decreased with DSm. In addition, the term of surface density of the octenyl succinic group (SD-OSG) was first proposed for modified starch granules, and it was proved better than DSm in interpreting the emulsifying capacities of starch granules with varying sizes. The present results implied that, as the particulate stabilizers, the optimal DSm of modified starch granules is size specific.