Fabrication and Characterization of Kafirin Microparticles Made Using Ionic Gelation Vibrational Jet Flow Technology: Influence of Processing Parameters on Physicochemical Properties

Kafirin is a protein from sorghum grain or its high-protein byproducts, including dried distillers' grain with solubles (DDGS) from bioethanol production. This highly hydrophobic and slowly digestible protein has demonstrated self-assembly properties, indicating its high potential for the manufacture of microparticles. In this study, DDGS kafirin microparticles were prepared using ionic gelation vibrational jet flow technology (IGVJFT). The effects of nozzle diameter (µm), integrated electrode voltage (V), internal frequency/vibration (Hz), gelation solution concentration (CaCl₂ [% w/v]), and kafirin concentration (% w/v) were evaluated. A fractional factorial design (2^5-1) of 16 processing runs was applied to model the influence of processing parameters on the microparticle physicochemical properties in terms of volume-weighted mean microparticle size (µm) and zeta potential (mV). The production runs yielded microscale particles with a volume-weighted mean microparticle size of 522-937 µm and zeta potentials ranging from -32.8 to -12.3 mV. Scanning electron microscopy revealed differences in the morphological microstructure. At lower protein concentrations, spherical particles with porous structures formed, whereas higher concentrations produced oval-shaped microparticles with an open, matrix-like architecture. Overall, IGVJFT produced DDGS kafirin microparticles with reproducibility, uniformity, and high-speed production. The kafirin concentration, nozzle diameter, integrated electrode voltage, and internal frequency were identified as the most significant parameters affecting DDGS kafirin microparticle size and zeta potential. This study provides a foundation for the use of IGVJFT by identifying its significant processing parameters required for large-scale optimization of kafirin microparticle production.