Subunit composition affects formation and stabilization of o/w emulsions by 11S seed storage protein cruciferin
Citation
Withana-Gamage, T.S., Hegedus, D.D., McIntosh, T.C., Coutu, C., Qiu, X., Wanasundara, J.P.D. (2020). Subunit composition affects formation and stabilization of o/w emulsions by 11S seed storage protein cruciferin. Food Research International, [online] 137 http://dx.doi.org/10.1016/j.foodres.2020.109387
Plain language summary
The major seed storage protein of Brassica oilseeds is cruciferin and it is composed of 6 subunits expressed by multiple genes. Experiments of this study used cruciferin expressed in Arabidopsis mutant lines carrying a single gene type therefore all 6 subunits of the protein are of same type. In Arabidopsis, three genes are primarily responsible for expressing three types of subunits, namely A, B and C. Cruciferin of these three mutant lines were separated and isolated to study their behavior in oil-water interfaces in order to predict their oil emulsification properties. Cruciferin composed of A or B subunits showed more or less emulsifying ability and stabilization at neutral pH. Cruciferin consisted of C subunits showed good oil emulsifying ability and emulsion stabilization ability when pH was as low as 2. Investigations support that at low pH (pH 2) cruciferin C subunits go though structural changes exposing more hydrophobic areas and allow binding of oil therefore improve emulsion stability. This information is useful in selecting genetic composition of cruciferin storage protein for improving low pH emulsification ability of protein.
Abstract
The 11S globulin cruciferin is the major storage protein in Brassicaceae/Cruciferae seeds and exists as a hexamer in its natural configuration. Arabidopsis thaliana cruciferin is composed of CRUA, CRUB and CRUC subunits. Wild type (WT) cruciferin and cruciferins composed only of identical CRUA, CRUB and CRUC subunits were examined for their ability to form and stabilize oil-in-water (o/w) emulsions. All proteins (0.9% at pH 7.4 and 2.0), except CRUC, formed stable canola oil or triolein emulsions with a dispersed phase volume fraction of 22–23%. A fine emulsion was formed by CRUB at pH 7.4 with droplet sizes of 6.8 and 8.6 μm for canola oil and triolein, respectively. The presence of 0.5 M NaCl reduced the level of adsorbed protein and protein load at the interface at pH 7.4, and resulted in emulsions that were less stable. Emulsions of CRUA and CRUB (pH 7.4, zero ionic strength, canola oil or triolein) had higher stability than emulsions with WT cruciferin up to 15 days after formation. CRUC formed a stable emulsion only at pH 2.0. The low solubility, low surface hydrophobicity and compact structure of the CRUC protein may contribute to its inferior emulsifying properties at neutral pH; however, acidic pH-induced dissociation of the hexameric assembly improved these properties. The abundance and exposure of hydrophobic residues in the hypervariable regions, extended loop regions, and solvent exposed surfaces of cruciferin are critical factors affecting o/w interface stabilization.