Removal of sinapine from canola protein isolates through washing with adsorbent resins as determined by Diffusion-Ordered Spectroscopy – Nuclear Magnetic Resonance (DOSY - 1H NMR)

Justification
The flavour profile of plant-based proteins is a major limiting factor that impairs their use as ingredients or additives in food applications. Sinapine is a major phenolic compound (>80%) found in canola and a contributing factor to the bitter taste present in the meals and protein. Hence, the removal of this compound could improve the quality of canola protein and expand its use as ingredient in food applications.

Objective
The aim of our study was to remove sinapine from canola proteins isolate (CPI) by washing with three macroporous absorbent resins namely Amberlite-XAD16N, Sepabeads-SP207 and Diaion-HP20. The impact of resin treatment on the proximate composition, functional properties and sinapine content was determined and compared with the unwashed CPI (control).

Methodology
Canola protein isolate was extracted and deflavoured via alkaline extraction - isoelectric precipitation (AE-IP). Deflavouring of the protein was carried out after the solubilization step by washing the solutions with adsorbent resins in a shaker for 2.5h (1:4 solid to liquid) at room temperature. Subsequently, the resins were removed by vacuum filtration, the proteins precipitated at pH 5.0 and freeze dried. The proximate composition and functional properties of the pre- and post-washed CPIs were determined and sinapine content of the samples analyzed using Proton - NMR and DOSY-NMR.

Results
Sinapine content in the washed CPIs reduced by ~99% ( <50 ppm) when compared to the control (1200 ppm). Similarly, the protein content, protein yield and solubility was enhanced by ~6%, 30% and 5% respectively. The results showed that adsorbent resin washing of CPI had no adverse effect on techno-functional properties such as emulsification, foaming, water and oil holding capacity when compared with the control (p>0.05).

Significance
The outcome of this study shows that coupling adsorbent resin washing with protein extraction could produce bland CPI with preserved or enhanced functionalities.