Multiresponse Surface Optimization of Ionic Gelation Vibrational Jet Flow Technology to Fine-Tune Kafirin Microparticles Extracted From Sorghum Dried Distiller's Grain.

Sorghum dried distiller's grain with solubles (DDGS), a protein-enriched byproduct of sorghum bioethanol production, is predominantly used as a low-cost animal feed. However, unutilized DDGS is mainly discarded as waste, containing approximately 40% of the prolamin protein kafirin. Kafirin's high hydrophobicity, low digestibility, evaporation-induced self-assembly, and strong disulfide cross-linking offer potential for biomaterial applications. This study used ethanol extraction and acid precipitation to purify kafirin protein from sorghum DDGS. The extracted protein was then used to prepare microparticles using ionic gelation vibrational jet flow technology (IGVJFT). This technology enables reproducible, uniform, scalable, high-speed microparticle production compared to existing methodologies. The integrated electrode voltage (V), internal frequency/vibration (Hz), and DDGS kafirin concentration (% [w/v]) used in the IGVJFT process were evaluated against key microparticle physicochemical response factors of volume-weighted mean microparticle size (% [w/v]), zeta potential (mV), and fracture frequency (mechanical strength) (%). Optimization of microparticle formation was performed by a response surface methodology (RSM) central composite design. Under different processing parameters of the RSM, the resulting DDGS kafirin microparticles possessed spherical morphology, volume-weighted mean particle sizes from 406.7 to 656.4 µm, zeta potential in the range of -38.2 to -18.1 mV, and fracture frequency (mechanical strength) of 23%-57%. Optimal conditions for producing microparticles with minimal size, high negative zeta potential, and low fracture frequency were identified and validated. These findings highlight the potential of DDGS kafirin as a sustainable material for large-scale microparticle applications and demonstrate the efficacy of IGVJFT for assembling hydrophobic proteins into microparticles with tailored physicochemical properties.