The influence of phytase on the solubility of storage proteins in rapeseed press cake

Rapeseed (Brassica napus subsp. napus) protein is gaining attention as a sustainable alternative protein source to animal derived proteins. Its utilization as a food ingredient for human consumption is hindered by the presence of phytic acid, or inositol hexaphosphate, an anti-nutritional factor that binds minerals and reduces protein solubility. This study investigates the effect of enzymatic hydrolysis of phytic acid, using phytase (12 U/mL) and phosphatase (0.44 U/mL), on the solubility of the two primary rapeseed storage proteins, cruciferin and napin. Rapeseed press cake was extracted in water (1:20 w/v) and incubated with enzymes for 60 min at 40 °C, followed by pH adjustment across a pH range of 4-9. Reversed-phase HPLC analysis confirmed that phytase treatment significantly (p ≤ 0.05) improved cruciferin solubility at pH 4 by up to 600 % by disrupting protein-phytate complexes, while napin solubility showed a minor, non-significant increase (p > 0.05). Additionally, ICP-OES analysis of minerals (Ca, K, Na, Mg, P and S) showed that phytase hydrolysis significantly increased soluble phosphorus, enhancing its bioavailability. These findings suggest that phytase treatment enhances the functional properties of rapeseed protein, improving its dispersion and solubility, and positioning it as a promising candidate for use in plant-based food formulations.