Front-face fluorescence spectroscopy study of globular proteins in emulsions: displacement of BSA by a nonionic surfactant.
The displacement of a globular protein (bovine serum albumin, BSA) from the surface of oil droplets in concentrated oil-in-water emulsions by a nonionic surfactant (polyoxyethylene sorbitan monolauarate, Tween 20) was studied using front-face fluorescence spectroscopy (FFFS). This method relies on measurement of the change in intensity (I(MAX)) and wavelength (lambda(MAX)) of the maximum in the tryptophan emission spectrum. A series of oil-in-water emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7.0) containing different molar ratios of Tween 20 to BSA (R = 0-131) were prepared. As the surfactant concentration was increased, the protein was progressively displaced from the droplet surfaces. At R > or = 66, the protein was completely displaced from the droplet surfaces. There was an increase in both I(MAX) and lambda(MAX) with increasing Tween 20 concentration up to R = 66, which correlated with the increase in the ratio of nonadsorbed to adsorbed protein. In contrast, there was a decrease in I(MAX) and lambda(MAX) with Tween 20 concentration in protein solutions and for R > or = 66 in the emulsions, which was attributed to binding of the surfactant to the protein. This study shows that FFFS is a powerful technique for nondestructively providing information about the interfacial composition of droplets in concentrated protein-stabilized emulsions in situ. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.
Rampon
V
V
Laboratoire d'Etude des Interactions des Molécules Alimentaires and Laboratoire de Physico-Chimie des Macromolécules, Institut National de la Recherche Agronomique (INRA), Rue de la Géraudière, 44316 NANTES Cedex 03, France.
Genot
C
C
Riaublanc
A
A
Anton
M
M
Axelos
M A V
MA
McClements
D J
DJ
D000327:Adsorption; D004655:Emulsions / Q000737:chemistry; D010316:Particle Size; D011136:Polysorbates; D012710:Serum Albumin, Bovine / Q000032:analysis / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013501:Surface-Active Agents / Q000032:analysis / Q000737:chemistry*; D014867:Water
D004655:Emulsions; D011136:Polysorbates; D013501:Surface-Active Agents; D014867:Water; D012710:Serum Albumin, Bovine