Surface-Directed Structure Formation of beta-Lactoglobulin Inside Droplets
Journal article, 2011
The morphology of beta-lactoglobulin structures inside droplets was studied during aggregation and gelation using confocal laser scanning microscopy (CISM) equipped with a temperature stage and transmission electron microscopy (TEM). The results showed that there is a strong driving force for the protein to move to the interface between oil and water in the droplet, and the beta-lactoglobulin formed a dense shell around the droplet built up from the inside of the droplets. Less protein was found inside the droplets. The longer the beta-lactoglobulin was allowed to aggregate prior to gel formation, the larger the part of the protein went to the interface, resulting in a thicker shell and very little material being left inside the droplets. The droplets were easily deformed because no network stabilizes them. When 0.5% emulsifier, polyglycerol polyresinoleat (PGPR), was added to the oil phase, the beta-lactoglobulin was situated both inside the droplets and at the interface between the droplets and the oil phase; when 2% PGPR was added, the beta-lactoglobulin structure was concentrated to the inside of the droplets. The possibility to use the different morphological structures of beta-lactoglobulin in droplets to control the diffusion rate through a beta-lactoglobulin network was evaluated by fluorescence recovery after photobleaching (FRAP). The results show differences in the diffusion rate due to heterogeneities in the structure: the diffusion of a large water-soluble molecule, FITC-dextran, in a dense particulate gel was 1/4 of the diffusion rate in a more open particulate beta-lactoglobulin gel in which the diffusion rate was similar to that in pure water.