Protein bodies from hemp seeds: Isolation, microstructure and physicochemical characterisation

Protein bodies are naturally occurring storage organelles in plant seeds. Although the microstructure of protein bodies has been studied, their physicochemical behaviour and stability under different environmental conditions remain poorly understood. In this study, hemp seed protein bodies (HPBs) were obtained using a sonicationassisted aqueous enzymatic extraction method. Then, their microstructures were characterised using various microscopic techniques. Next, the protein composition was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Lastly, the influence of pH (2-13) on the colloidal stability and structural integrity of aqueous HPB dispersions was investigated. Detailed microscopic examination showed that the HPBs exhibited spherical shape with an average diameter of about 4.6 mu m. The structure consisted of a protein crystalloid and several phytin globoids, all surrounded by a proteinaceous matrix and a single membrane. Globulin edestin was the most abundant storage protein in the HPBs as revealed by SDS-PAGE. The HPB dispersions exhibited excellent colloidal stability only at neutral pH as opposed to their aggregation and/or solubilisation at other pH levels tested. The HPBs also showed irreversible structural changes in response to pH variation. Specifically, little to no swelling of the particles was observed at pH 5 (around the isoelectric point (pI) of the hemp protein). However, when the pH shifted away from the pI, swelling, rupture and eventual dissolution of the particles were pronounced under both extreme acidic and alkaline conditions. These physicochemical behaviours make the HPBs an interesting pH-sensitive material for food applications, which will be explored in subsequent studies.