Preparation and Structural Characterization of Micron-Sized Natural Starch Microspheres via the Membrane Emulsification Method

Starch microspheres with uniform morphology and controllable particle size show significant application value. In this work, micrometer-sized natural starch microspheres (SMs) were prepared via membrane emulsification for the first time. Transmembrane pressure and the dispersed phase concentration significantly affect the morphology of SMs. The average particle size decreased with an increase in the transmembrane pressure, while a higher dispersed phase concentration yielded a more uniform particle size distribution. Under optimized membrane emulsification conditions (0.2 MPa and 10% dispersed phase concentration), debranched corn starch microspheres (CSM, 7.93 ± 0.12 μm) and debranched amaranth starch microspheres (ASM, 0.95 ± 0.01 μm) were successfully prepared. Gel permeation chromatography (GPC) analysis showed that the SMs had a lower molecular weight dispersity (D̅) than that of debranched starch (from 2.18 to 1.36 for CSM and from 2.04 to 1.59 for ASM), indicating a narrower molecular weight distribution and more densely arranged molecular chains. The crystallinity of conventional starch microspheres was generally lower than that of native starch because the ordered structure of starch molecules was destroyed during the microsphere formation process. Whereas, the SMs prepared in this work exhibited a significant increase in crystallinity compared with native starch (from 18.7 to 58.52% for CSM and from 25.8 to 69.67% for ASM), which was significantly higher than that of starch microspheres reported in previous papers. DSC proved that the gelatinization temperatures of SMs were higher than 90 °C, indicating that our SMs were difficult to gelatinize under conventional conditions. Because of the controllable particle sizes, the SMs prepared in this study had a narrow molecular weight distribution, extremely high crystallinity, and resistance to gelatinization, thus having broad application prospects in food, medicine, and other material fields.