Jan Alsins

Competitive protein adsorption between bovine serum albumin and β-lactoglobulin during spray-drying

Abstract Competitive adsorption between bovine serum albumin (BSA) and β-lactoglobulin (β-Lg) during spray-drying was studied and the results were compared to the adsorption of single protein at the powder surface. The study was performed with a new method using fluorescence quenching of pyrene labelled proteins at the powder surface. Comparing the single adsorption of the two proteins during spray-drying showed a similar adsorption behaviour with little preferential adsorption of one protein over the other. Analysis of the powder surface after spray-drying a mixture of BSA and β-Lg in a dextran matrix indicated that β-Lg adsorbed to the surface in preference to BSA at lower concentrations, but at higher concentrations the effect was less pronounced. When one of the proteins was spray-dried in a surplus of the second protein the adsorbed amount of the protein studied showed a strong decrease in apparent surface load at higher concentrations. However, at lower concentrations the adsorption seemed to be independent of the other protein present. This was the case for both BSA and β-Lg. In the single adsorption study of β-Lg the apparent surface load of β-Lg was measured to be 1.1xa0mg/m 2 at a concentration of 10% β-Lg in the powder.

A fluorescence method for quantitative measurements of specific protein at powder surfaces

Abstract A new method using fluorescence labelled proteins was developed to determine the quantitative amount of specific protein at the powder surface. The method is based on steady-state fluorescence measurements of pyrene labelled proteins with oxygen gas phase quenching at the powder surface. The surface load of protein was measured for spray-dried dextran powders containing bovine serum albumin (BSA). The results show a patchwise surface load of about 1.3 mg m−2 at a concentration of 0.33% (dry weight) BSA in the powder. The patchwise surface load stays constant with increased BSA concentration in the powder.

Structure and photophysical properties of novel ruthenium(II) complexes containing 6-substituted bipyridines

A series of novel tris(bpy) ruthenium(II)-type complexes (where bpy = 2,2-bipyridine) Ru(bpy)(2)(6-carboxylato-2,2-bpy) hexafluorophosphate, Ru(bpy)(2)((2,2-bpy-6-yl)-acetic acid) dihexafluorophosphate, Ru(bpy)(2)(6-methoxycarbonyl-2,2-bpy) dihexafluo

Competitive protein adsorption between b-casein and b-lactoglobulin during spray-drying: effect of calcium induced association

Competitive adsorption between -casein and -lactoglobulin (-Lg) during spray-drying was studied by the new surface sensitive technique using fluorescence quenching of pyrene labelled protein at the powder surface. The difference in competitiveness of -casein when present as monomers and as associated into micellar like structures were studied. Results were compared with the adsorption of single proteins at the powder surface. The adsorption of monomeric -casein alone gave an apparent surface load of ≈1 mg/m2 at a protein concentration of 0.3% dry weight and then remained constant with an increasing protein concentration. In the presence of Ca2+, associated -casein gave a lower affinity adsorption than monomeric -casein and did not reach a plateau value, instead it continued to increase with an increasing protein concentration. -Lg showed a low-affinity adsorption during spray-drying compared to monomeric -casein, although not as low as associated -casein. Competitive adsorption between monomeric -casein and -Lg resulted in a higher apparent surface load of -casein than -Lg at both protein concentrations studied (total 0.3 and 3.3% dry weight). However, in an associated form -casein was less competitive than -Lg. At a low bulk protein concentration (0.3% dry weight) -Lg dominated the powder surface, whereas at a higher concentration (3.3% dry weight) there was little difference between the proteins. The results indicate that the competitiveness of a protein during spray-drying is highly influenced by the ability of the protein to attach and rearrange at the droplets air–water interface during the spray-drying process. (Less)

Dimer formation of a stilbenesulphonic acid salt in aqueous solution

The steady-state and time-resolved fluorescence and H-1 NMR spectra of a stilbenesulphonic acid salt, commonly used as an optical brightening agent, was studied as a function of concentration in aqueous solution. The aggregates, formed at higher concentra

Effects of dimensionality on diffusion-controlled deactivation of excited species

The kinetics of diffusion-controlled deactivation processes is strongly affected by confinement of the reacting species in a space kept at molecular dimensions in at least one direction. In globular micelles the confinement is in all three dimensions, and the well-known kinetics is determined by a first-order rate constant representing the frequency of encounters of a pair of reactant molecules in the micelle, and the statistics of distribution of the reactants over the micelles. If the confinement is allowed to grow in one dimension into rods, or two dimensions into monolayers or bilayers, or in all three dimensions to a homogeneous solution, the deactivation kinetics is determined by one-, two-, or three-dimensional diffusion. Experimental examples of these cases are presented. Further complications occur on timescales where migration of the reactants between the dimensionally restricted structures must be considered. Of particular interest are systems which comprise clusters of small micelles, where the exchange between the micelles in a cluster is rapid. Experimental results for such a system composed of reversed AOT micelles is presented.

Diffusion-Controlled Fluorescence Quenching in Micelles

The overall decay of fluorescence from an ensemble of small micelles containing fluorescent probes and quenchers is adequately described by a wellknown model due to Infelta et al.(Infelta PP, Gratzel M, Thomas JK (1988) J Phys Chem 78:190). It is determined mainly by the statistics of distribution of the quenchers: in micelles containing quenchers the decay is rapid, whereas the decay from probes excited in micelles without quenchers is slow and equal to that of the unquenched excited state, if no migration occurs.