Surface topography of heat-set whey protein gels by confocal laser scanning microscopy

Extensive research works have been carried out in investigating the microstructure of heat-set whey protein gels and their fractal nature, but little has been done on the surface studies of these systems due to the lack of suitable technique for surface characterization of wet and deformable food gels. This work intended to explore the possibility of applying confocal laser scanning microscope (CLSM) for surface characterization of such delicate systems. Surfaces of heat-set whey protein gels (14 wt%) have been investigated with and without the presence of salt (0 and 200 mM NaCl). High quality surface images across X–Z plane were obtained. These images were further analysed for their surface roughness, periodic length scale, and fractal nature. The roughness of these surfaces was quantified in terms of root-mean-square surface roughness (Rq) and arithmetic surface roughness (Ra). It was found that the protein gel without salt addition had a very smooth surface with Rq of 0.20 and 0.18 μm, respectively, but the gel containing 200 mM NaCl had a much rougher surface with large Rq and Ra (2.39 and 1.91 μm, respectively). The fractal nature of the surface was also revealed for this gel and a fractal dimension of 1.15 was obtained.