Relation between the gel structure and the mobility of tracers in globular protein gels

Abstract

Diffusion of fluorescent-labeled dextran with different molecular weights was investigated in β-lactoglobulin (β-lg) solutions and gels over a wide range of salt and protein concentrations at pH 7 by combining confocal laser scanning microscope (CLSM) with fluorescence recovery after photobleaching (FRAP). Effects of the protein concentration, the salt concentration and the tracer size were investigated in detail. Diffusion in turbid heterogeneous gels formed at 0.2M NaCl depended weakly on the probe size and the protein concentration and remained close to that in unheated solutions. A strong decrease of the diffusion coefficient with increasing tracer size and protein concentration was observed in more homogeneous gels formed at lower salt concentrations. Larger dextran chains were trapped in transparent gels formed at NaCl concentration below 0.1M. The present investigation complements an earlier study of tracer diffusion of larger spherical probes in β-lg gels using multi-particle tracking.