Structuring and functionalization of dispersions containing egg yolk, plasma and granules induced by mechanical treatments
Résumé
In this study, the impact of mechanical treatments on the physicochemical and emulsifying properties of hen egg yolk and its fractions plasma and granules has been assessed. Yolk, plasma, and granule dispersions at pH 4.0 and 0.75 M NaCl were subjected to rotor-stator and high-pressure pretreatments at different dynamic pressure levels: 30, 100, and 200 bar at 20 degrees C. Physicochemical characteristics (protein solubility, rheological behavior, and micro- and ultra-structures) and emulsifying properties (oil/water 60:40 emulsions: droplet size and flocculation, protein adsorption) of control dispersions and dispersions subjected to mechanical pretreatments (rotor-stator or high pressure) were compared. Homogenization at high pressures (100 and 200 bar) led to a decreased protein solubility and to an increase in apparent viscosity of yolk and plasma dispersions. These pressures certainly disrupted low-density lipoproteins (LDL) particles and generated aggregates of protein! s liberated from LDL and livetins in the plasma fraction, and led to a moderated reorganization of the microstructure of granules. Despite the modifications observed in the pretreated plasma and granules dispersions, the oil droplet diameter and the bridging flocculation obtained in emulsions made with these dispersions were similar to that obtained with untreated dispersions. Results concerning interfacial protein adsorption suggested that preformed or natural aggregates at least partially persist at the oil-water interface.