The gelation properties of rapeseed proteins are barely affected by co-extracted phenolic compounds

Rapeseed proteins are a promising alternative to animal-based proteins that can form gels to provide structure in foods. However, in the case of plant proteins, co-extracted impurities, such as phenolic compounds, may interfere with the protein network. Phenolic compounds in rapeseeds are found mainly in the form of sinapic and ferulic acid in the kernels and as proanthocyanidins in the hulls. These can be co-extracted with the proteins and may affect the protein gel properties. Therefore, the current study elucidates this potential effect of phenolics on the protein gel properties. An extracted rapeseed protein isolate was mixed with sinapic and ferulic acid or with proanthocyanidins in a natural ratio at pH 7 or 9, and the effects of the phenolic compounds on the rheological properties of the gel obtained after heating were quantified. The gels made by mixing proteins and phenolic compounds were compared with gels made up of natural protein extracts where sinapic acid, ferulic acid, and proanthocyanidins were naturally present. Shear rheometry revealed only minor differences in the rheological behaviour of the gels with protein-phenolic blends. Furthermore, only minor differences in protein dispersibility or cross-linking were observed before gelation, regardless of the environmental pH, indicating weak interactions between proteins and phenolics. In contrast to common practice, phenolic compounds do not need to be removed from the protein extracts, which enables protein extraction in more simple steps, thereby making the protein extraction process more efficient, in terms of costs and energy.