| In situ sol-gel transition of beta-lactoglobulin (BLG) induced by heating, and concomitant changes in gel microstructure and rheological properties were investigated using confocal laser scanning microscopy (CLSM), small-amplitude oscillatory shear, uniaxial compression, and differential scanning calorimetry. The effects of four critical factors, pH (2, 5, and 7), protein concentration (5, 10, and 15%), salt concentration (NaCl 0, 0.1, and 0.3 M), and heating rate (1, 5, and 10°C/min) were studied.; Some basic techniques were developed to quantify and visualize the time-resolved, in situ two-dimensional (2D) and three-dimensional (3D) microstructural characteristics of BLG gels. The CLSM images were obtained continually during heating up to 95°C. The images were processed for correcting imaging errors such as z-axis alignment, light attenuation, noise, and uneven intensity of the micrographs. Subsequent 2D and 3D analyses of the images provided a number of objective image features such as area, perimeter, and volume of protein clusters, as well as gelation temperatures. These parameters were used as structural indices to represent the gel properties.; BLG molecules aggregated and formed a network during gelation. Shape and size of the BLG clusters were dependent on the gelation conditions. As BLG concentration increased, the morphological parameters such as average area and volume of protein clusters, elastic modulus (G'), and failure stress increased with protein content, whereas gelation temperatures (Ti, Thalf-max, T0, Tpeak, and Tf) and failure strain decreased. High electrostatic repulsions produced the stranded-clusters of the BLG molecules with small fractal dimension (Df), while less electrostatic repulsions provided the particulate shape of the BLG clusters with large Df. BLG gels formed at pH 7 were strong and deformable, whereas those formed at pH 2 were weak and brittle. At pH 2 and 7, the average area and volume of protein clusters increased with salt content adding particulate features. Different heating rates altered the effect of other factors on BLG gels. |
