title: Surface-directed structure formation of β-lactoglobulin inside droplets.
abstract: The morphology of β-lactoglobulin structures inside droplets was studied during aggregation and gelation using confocal laser scanning microscopy (CLSM) 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 β-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 β-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 β-lactoglobulin was situated both inside the droplets and at the interface between the droplets and the oil phase; when 2% PGPR was added, the β-lactoglobulin structure was concentrated to the inside of the droplets. The possibility to use the different morphological structures of β-lactoglobulin in droplets to control the diffusion rate through a β-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 β-lactoglobulin gel in which the diffusion rate was similar to that in pure water.
authors.affiliation: SIK, The Swedish Institute for Food and Biotechnology, SE-402 29 Göteborg, Sweden. camilla.ohgren@sik.se
authors.forename: Camilla
authors.initials: C
authors.lastname: Ohgren
authors.forename: Niklas
authors.initials: N
authors.lastname: Loren
authors.forename: Annika
authors.initials: A
authors.lastname: Altskar
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Hermansson
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000032:analysis; D002417:Cattle; D003692:Delayed-Action Preparations / Q000138:chemical synthesis* / Q000378:metabolism; D003911:Dextrans / Q000032:analysis; D004058:Diffusion; D016503:Drug Delivery Systems / Q000379:methods; D045703:Emulsifying Agents / Q000737:chemistry* / Q000378:metabolism; D004655:Emulsions / Q000737:chemistry* / Q000378:metabolism; D005229:Fatty Acids, Monounsaturated; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives / Q000032:analysis; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D010169:Palmitic Acids / Q000032:analysis; D010938:Plant Oils / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D000074262:Rapeseed Oil; D013050:Spectrometry, Fluorescence
chemical_list: C543305:4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-hexadecanoic acid; D001896:Boron Compounds; D003692:Delayed-Action Preparations; D003911:Dextrans; D045703:Emulsifying Agents; D004655:Emulsions; D005229:Fatty Acids, Monounsaturated; D005456:Fluorescent Dyes; D007782:Lactoglobulins; D010169:Palmitic Acids; D010938:Plant Oils; D000074262:Rapeseed Oil; C015219:fluorescein isothiocyanate dextran; D016650:Fluorescein-5-isothiocyanate