Impact of canola seed dehulling and pressing temperature on the microstructure of canola meals, protein structure within the meals, and protein isolate extraction and properties

Abstract

Canola hulls are rigid structures rich in lignocellulosic polymers and tannins. With the growing demand for sustainable proteins and advances in dehulling technology and hull utilization, dehulling canola seeds before pressing could be a viable way to improve meal and protein quality. This study examined the combined effects of dehulling and pressing temperature (40, 80, and 120 ℃) on canola meals and their derived protein isolates. The removal of ~80-85% of hulls reduced heat-induced aggregation and preserved more of the meal’s native microstructure during pressing, especially at 120 °C. Moreover, the secondary and the tertiary structure of meal proteins were better preserved, particularly under higher treatment temperatures. These improvements were attributed to the reduction of friction-induced effects and covalent modifications of proteins during the press resulting from dehulling. The above-mentioned observations directly corresponded with protein extraction efficiency values under alkaline (pH 11) and salt (0.8 M NaCl) conditions. Dehulling significantly increased extraction efficiency of alkaline and salt isolates by an average of 10.49% and 8.12%, respectively, with the differences between non-dehulled and dehulled meals becoming more pronounced as the pressing temperature increased. The observed improvements were associated with higher extraction of unfolded cruciferins and aggregates from dehulled meals, particularly under alkaline conditions. Dehulling also improved isolate protein content, however, its effects on isolate color, protein structure and aqueous solubility were more nuanced. Overall, dehulling can be an effective technique for preserving the structure of canola meal, increasing protein thermal stability during pressing, and improving isolate extraction efficiency and protein content.