Formation of kafirin microparticles by phase separation from an organic acid and their characterisation

Protein microparticles (microspheres) have numerous food and pharmaceutical applications. However, generally preparation of prolamin protein microparticles involves aqueous ethanol as a solvent. An ethanol-free method of making microparticles from kafirin with a novel structure was devised. Glacial acetic acid or other organic acids were used as kafirin solvent and the microparticles formed by phase separation on addition of water. The kafirin microparticles were characterised by light microscopy, scanning electron microscopy and transmission electron microscopy and their size distribution was measured. The kafirin microparticles prepared by phase separation from organic acid were spherical or irregular shaped, between 1 and 10 μm in diameter, with rough, porous outer surfaces and many internal holes or vacuoles. The holes seem to be the footprint of air bubbles which were entrapped during microparticle preparation. With an increase in the final concentration of acetic acid, the structure of the microparticles changed from porous spheres to an open matrix, with a concomitant change in kafirin secondary structure from α-helical to β-sheet, indicative of protein aggregation. These highly vacuolated and open matrix type microparticles appear to have potential as encapsulating agents and support structures.