Effect and Underlying Mechanism of Degree of Gelatinization of Potato Starch on Emulsion Stability

In this study, emulsions containing 30% (m/m) oil phase were prepared using potato starch with different degrees of gelatinization (DSG) and corn oil. The effect of DSG on the stability of the emulsions was evaluated by through measurement of the storage stability, Fourier transform infrared spectra (FTIR), Turbiscan stability index (TSI), particle size, microstructure, and rheological properties. The results showed that the stability of the emulsions initially increased and then decreased with the increase in DSG. As DSG increased up to 67.03%, the characteristic FTIR peaks of water and starch molecules became more pronounced, and the particle size and TSI of the emulsions decreased. This was attributed to an increase in the hydrophobicity of starch and the leaching of amylose following gelatinization, which led to more starch granules participating in the emulsion formation and increased coverage of starch granules on droplets, thereby resulting in smaller droplet sizes and a more stable emulsion. Potato starch with 67.03% DSG resulted in the smallest droplet size and TSI and the best emulsion stability. Increasing DSG (≥ 71.81%) resulted in increased leaching of amylose, leading to chaotic entanglements that hindered the oil phase from integrating into the starch and thereby resulting in larger particle sizes and reduced stability. Moreover, the emulsion containing potato starch with DSG equal to or larger than 64.14% remained stable without any phase separation for 21 days. Laser scanning confocal microscopy (LSCM) observations and rheological analyses of the emulsions showed that the strength of the gel structure was closely correlated to the interaction among oil droplets. Denser arrangement of oil droplets conferred higher apparent viscosity and storage modulus and stronger gel network structure. Additionally, the reduction in the absolute value of the zeta potential of the starch after gelatinization facilitated the proximity of the granules to each other and also increased the strength of the network structure among granules in the continuous phase, thus resulting in improved emulsion stability. This study contributes to a deeper understanding of the mechanism by which gelatinized starch stabilizes emulsions and is of great significance to the development of more stable starch-based emulsions.