Emulsifying properties of canola and flaxseed protein isolates produced by isoelectric precipitation and salt extraction

The emulsifying (emulsion capacity (EC), emulsion activity/stability indices (EAI-ESI) and creaming stability (CS)) and physicochemical (surface charge/hydrophobicity, protein solubility, interfacial tension, and droplet size) properties of canola (CaPI) and flax (FlPI) protein isolates produced by isoelectric precipitation and salt extraction were investigated relative to whey protein isolate (WPI). Both protein source and method of production were found to have significant effects on the physicochemical and emulsifying properties of both protein isolates. All proteins carried a net negative charge at neutral pH, whereas surface hydrophobicity for CaPI and FlPI (~120.6) was found to be significantly higher than that of WPI (~61.9). CaPI and FlPI produced by salt extraction showed higher solubility and interfacial activity compared to those produced by isoelectric precipitation. CaPI showed significantly higher EC (~515.6g oil/g protein) than FlPI (~498.9g oil/g protein) which was comparable to WPI (520.0g oil/g protein). However, EAI and ESI values for CaPI and FlPI were significantly lower than that of WPI. The mean EAI value for FlPI was higher (~40.1m²/g) than CaPI (~25.1m²/g) however, ESI values of CaPI and FlPI were similar. Creaming stability of emulsions stabilized by CaPI and FlPI ranged between 86.1 and 96.6%, which was comparable to WPI-stabilized emulsions (90.8%). The mean droplet diameter for FlPI-stabilized emulsions (~11.7μm) was smaller than that of CaPI-stabilized emulsions (~14.8μm). The EC of CaPI and FlPI was related to their solubility, surface characteristics and ability to reduce interfacial tension, while emulsion stability was a function of solubility, surface characteristics and droplet size. These results suggest that CaPI and FlPI have emulsion forming properties; however their stability is low when compared to WPI.