Characterization of rapeseed protein supramolecular structures obtained by aqueous extractions

Aqueous extraction of rapeseed has the potential to produce mildly refined yet functional protein ingredients. However, the colloidal structures of these mildly refined ingredients are still not fully understood. Therefore, the aim of this work was to examine the structures present in rapeseed extracts by analyzing their scattering characteristics across different length scales. Rapeseed protein concentrates were obtained after aqueous extractions at acidic (pH 5.7) or alkaline (pH 8.5) conditions. The structures were investigated using complementary techniques, cryo-transmission electron microscopy, small angle X-ray scattering and small angle neutron scattering. To understand the scattering contribution of various components at characteristic length scales, D₂O contrast variation was performed, and SAXS analysis for extracts at pH 5.7 treated with pectinase were compared to those untreated. All suspensions contained globular proteins within a network of soluble polysaccharides as observed by Cryo-TEM. SANS analysis with different D₂O/H₂O ratios demonstrated that at low q, both proteins and polysaccharide contributed to scattering, suggesting the presence of large complexes containing both. The signal for pH 8.5 suspensions was mainly attributed to oleosomes. SAXS measurements agreed with the SANS data, and pH 5.7 suspensions measured after pectin hydrolysis revealed that the complexes were formed by rapeseed globulins (∼4 nm) and polysaccharide chains. This research highlights the importance of understanding the protein-polysaccharide interactions occurring in rapeseed aqueous extracts, to fully utilize these less refined fractions as value-added ingredients in future sustainable foods.