Emulsifying properties of collagen fibers: Effect of pH, protein concentration and homogenization pressure

The emulsifying properties of collagen fibers were evaluated in oil-in-water (O/W) emulsions produced under different conditions of pH, protein content and type of emulsification device (rotor-stator and high-pressure homogenizer). The stability, microstructure and rheology of the O/W emulsions were measured. The phase separation and droplet size of the emulsions prepared using the rotor-stator device (primary emulsion) decreased with protein concentration and reduction in pH, allowing the production of electrostatically stable emulsions at pH 3.5. In contrast, emulsions at higher pH values (4.5, 5.5 and 7.5) showed a microscopic three-dimensional network responsible for their stability at protein contents higher than 1.0% (w/w). The emulsions at pH 3.5 homogenized by high pressure (up to 100 MPa) showed a decrease in surface mean diameter (d(32)) with increasing pressure and the number of passes through the homogenizer. These emulsions showed droplets with lower dispersion and d(32) between 1.00 and 4.05 mu m, six times lower than values observed for primary emulsions. The emulsions presented shear-thinning behavior and lower consistency index and viscosity at higher homogenization pressures. In addition, the emulsions showed a less structured gel-like behavior with increase in homogenization pressure and number of passes, since the pressure disrupted the collagen fiber structure and the oil droplets. The results of this work showed that the collagen fiber has a good potential for use as an emulsifier in the food industry, mainly in acid products. (C) 2010 Elsevier Ltd. All rights reserved.