Emulsions stabilized by heat-treated collagen fibers

The emulsifying properties of collagen fiber were modified by heat treatment at temperatures ranging from 50 to 85 degrees C for 20 or 60 min. In addition to heat treatment, the influence of pH (3.5 and 9.2) and the emulsifying process (rotor-stator device and high-pressure homogenizer) were evaluated on oil-in-water emulsions stabilized by collagen fiber through visual analysis (stability), microstructure and rheological measurements. Emulsions homogenized using solely the rotor-stator device showed phase separation and a larger mean droplet size (d(32)), except for the emulsion composed by non-heated collagen fiber. The alkaline emulsions showed lower kinetic stability, since collagen fibers have a lower net charge (zeta potential) at higher pH values, decreasing the electrostatic stability process. Heat treatment slightly decreased the protein charge and significantly reduced the insoluble protein content, suggesting a decrease in the emulsifying properties of the collagen fiber. The use of high-pressure homogenization (20-100 MPa) made it possible to produce acid emulsions with a reduced droplet size and distribution. At 20 MPa, the emulsions showed a higher d(32) value (between 3.17 and 1.18 mu m), while at 60 and 100 MPa the emulsions presented lower d(32) values (between 0.74 and 0.94 mu m) without any significant variation between the different heat-treated collagen fibers, but showing a noticeable decrease in emulsion viscosity and elasticity with increases in the homogenization pressure and heat treatment. (C) 2011 Elsevier Ltd. All rights reserved.