Ulla M. Elofsson

Surface composition of spray-dried milk protein-stabilised emulsions in relation to pre-heat treatment of proteins.

Several important technical properties of spray-dried food powders depend on particle-liquid interactions (e.g. wettability, dispersability) and particle-particle interactions (e.g. flowability). It can be assumed that the chemical composition of the surface layer of the particles to a large extent determine these properties. The present study has been aimed to investigate the relation between the surface composition of spray-dried milk protein-stabilised emulsions and pre-heat treatment of the proteins. Solutions of WPC were heat-treated at low (60-90 degrees C) and high (140 degrees C) temperature and the degree of denaturation was determined, prior to the preparation of emulsions with rapeseed oil. The surface composition of the dry powders were established by using ESCA (electron spectroscopy of chemical analysis). The emulsions were characterised by droplet size distribution before spray drying and after dissolution of the powders. Also free fat extractions and estimations of wettability (dissolution rates) were performed. The powder surface coverage of protein decreased with increasing degree of protein denaturation before the emulsification, whereas the emulsion droplet size increased both before spray drying and after reconstitution of powders. The free fat extraction as well as the dissolution rate, whereof the latter decreased with increasing surface fat coverage, correlated well with the fat coverage of the powder surface.

Heat induced aggregation of b-lactoglobulin studied by dynamic light scattering

The in situ heat-induced aggregation of commercial β-lactoglobulin as such, or after further purification, was followed to a z-average hydrodynamic diameter of 15–20 nm at 59–63 °C by dynamic light scattering. In this temperature range, measurable increase of hydrodynamic diameter occurred after an apparent lag period, which was strongly dependent on heating temperature, pH and initial protein concentration. The changes in time scale of the aggregation process agreed with changes in amount of unfolded β-lactoglobulin, assuming a two-state model of the denaturation. The pH dependence reflected the midpoint unfolding temperature and not the sulphydryl group reactivity, suggesting that this reactivity was not rate limiting in the aggregation. The aggregation process was modelled numerically with FuchsSmoluchowski kinetics.

Adsorption of lysozyme, beta-casein and their layer-by-layer formation on hydrophilic surfaces: Effect of ionic strength

The adsorbed amount and layer structure of lysozyme, beta-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and beta-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though beta-casein and silica are negatively charged at the pH used. No beta-casein remained adsorbed after rinsing with a 150mM buffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. beta-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and beta-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/beta-casein layers contain higher amounts of protein compared to those of pure lysozyme or beta-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and beta-casein. The protein layers are probably highly interpenetrated with no clear separation between them.

Salivary protein adsorption onto hydroxyapatite and SDS-mediated elution studied by in situ ellipsometry

Whole unstimulated saliva from two donors was investigated both with respect to adsorption characteristics and SDS‐induced elutability. Salivary protein adsorption onto hydroxyapatite (HA) discs was studied by means of in situ ellipsometry in the concentration range 0.1–20% saliva. The adsorbed amounts on HA were found to be similar to those on silica, but the rates of adsorption were lower. Protein adsorption was virtually unaffected by the presence of Na+, whereas Ca2+ induced nucleation of calcium phosphate at the surface, the deposition rate being influenced by the pellicle age but not by the presence of saliva in bulk solution. The SDS elutability of adsorbed pellicles was determined on HA as well as on silica surfaces. Desorption from both surfaces was found to occur in the same SDS concentration range, although a residual layer was observed on HA. The slight net positive charge and lower charge density of HA as compared to the strongly negatively charged silica, may, at least partly, account for this observation by causing a reduction in the repulsive force between protein‐surfactant complexes and the surface. Inter‐individual differences, observed in the adsorption as well as elution experiments, are thought to relate to the compositional differences observed by SDS‐PAGE.

Adsorption of β-lactoglobulin A and B: Effects of ionic strength and phosphate ions

Abstract The effect of ionic strength in phosphate buffer and in pure NaCl solution on the adsorption onto hydrophilic and methylated silica surfaces for β-lactoglobulin A and B was studied by in-situ ellipsometry. On hydrophilic silica, increased absorbed amounts as well as faster kinetics were found for β-lactoglobulin (β-lg) B with increasing ionic strength in pure NaCl solution. The absorber plateau values obtained for the A variant were seen to be unaffected by ionic strength both in pure NaCl solution (on methylated silica) and in the presence of phosphate (on methylated as well as on hydrophilic silica). A decrease in adsorbed amounts, for β-lg B on the two types of surface and for a 1:1 mixture of the A and B variants on methylated silica in the presence of phosphate at high ionic strength (I = 0.17) suggested a specific interaction with phosphate ions for the B variant. The interaction takes place only at higher ionic strength and probably gives rise to increased dissociation of the dimers.

Studies on the exchange of early pellicle proteins by mucin and whole saliva

Adsorption of small pellicle proteins statherin or proline-rich protein 1 (PRP1), respectively, and subsequent adsorption of human whole saliva (HWS) or salivary mucin MUC5B, respectively, was studied using ellipsometry and total internal reflectance fluorescence. Differences in elution (using sodium dodecyl sulphate (SDS) solutions) between mixed and single protein films were also investigated. On both hydrophilic and hydrophobized surfaces HWS and MUC5B were found to adsorb to pre-adsorbed layers of statherin and PRP1, respectively. Statherin adsorption on both substrate types showed no or minor exchange by HWS or MUC5B and no change in SDS elution between mixed and single protein films. Small amounts of PRP1 were exchanged by HWS on both surface types and the SDS elutable fractions were similar or larger for mixed films compared to single protein films. PRP1 and MUC5B in sequence showed minor exchange of PRP1 on hydrophilic surfaces, while no exchange could be established on hydrophobized substrates. SDS elutable fractions decreased for PRP1 and MUC5B mixed films compared to single protein films. In conclusion, minor amounts of statherin and PRP1 are exchanged during the time course of the experiments, which indicates that these proteins may to a large extent remain incorporated in the pellicle.

Stability of spray-dried protein- stabilized emulsions—effects of different carbohydrate additives

Stability of spray-dried protein-stabilized emulsions : Effects of different carbohydrate additives

Adsorption Studies of Interaction Between Water-Extractable Nonstarch Polysaccharides and Prolamins in Cereals

ABSTRACT Adsorption of cereal storage protein and nonstarch polysaccharides onto methylated silica surfaces, as measured by ellipsometry, was used to study possible interactions between those components. All fractions, rye secalin, wheat gliadin, rye arabinoxylan, and wheat arabinogalactan peptide, were surface-active to some degree. Sequential adsorption of rye arabinoxylan and wheat arabinogalactan peptide on top of gliadin and secalin, respectively, indicated that an interaction occurred. As ionic strength and pH influenced both the adsorption and the interaction of the components studied, these phenomena are believed to be of electrostatic nature.