Evaluation of canola protein functionality in mixed food systems

Abstract

Oilseed proteins contribute useful functionality to food systems. Knowledge of the molecular interactions between plant proteins such as commercial canola protein isolate (CPI) and hydrocolloids such as K-carrageenan (k-CAR) and guar gum will allow the manipulation of physical and textural properties of mixed biopolymers by adjusting the interaction in a desirable way. This research investigates the molecular interactions involved in gelation and emulsification of these CPI-hydrocolloid systems. The objectives were to: a) determine the functional and physicochemical properties of CPI-k-CAR and CPI-guar gum mixtures; b) determine the type and degree of interactions between CPI and k-CAR or guar gum based on protein conformational changes assessed by differential scanning calorimetry, fluorescence spectroscopy and microscopy; and c) establish optimum conditions for gelation and emulsification of these systems. Gelling characteristics and emulsifying properties were evaluated using dynamic rheology and spectroturbidimetry, respectively. This study has 1) characterized the gel properties of CPI-k-CAR and CPI-guar gum mixtures using dynamic rheology and microscopy; 2) optimized conditions for specific functional properties such as network and emulsion formation. Optimum conditions for gelation of CPI-k-CAR mixtures were pH 6, 3% (w/v) k-CAR, 0.05 M NaCl, 15% (w/v) CPI; whereas those for CPI-guar gum mixtures were pH 10, 1.5% (w/v) guar gum, 0.05 M NaCl, 20% (w/v) CPI. Electrostatic complexing and synergistic interaction contributed to the formation of strong and elastic CPI-k-CAR gels. The synergistic behaviour was supported by the microstructural data of gel networks. Furthermore, optimum conditions for CPI-k-CAR-stabilized emulsions were pH 6, 1% (w/v) k-CAR, 0.25 M NaCl, 10% (w/v) CPI; whereas those for CPI-guar gum-stabilized emulsions were pH 10, 3% (w/v) guar gum, 0.25 M NaCl, 10% (w/v) CPI; 3) confirmed that hydrophobic interactions, hydrogen bonding and disulfide linkages are the main molecular forces involved in the formation and stabilization of CPI-k-CAR and CPI-guar gum gels and emulsions; 4) reported improvements in the emulsifying properties and surface hydrophobicity of these CPI-hydrocolloid mixtures, when compared to CPI alone. Protein-polysaccharide interactions give a realistic indication of plant proteins behaviour in food systems and provide useful information for the development of functional canola protein products.