Phase separation in amorphous hydrophobically modified starch-sucrose blends: Glass transition, matrix dynamics and phase behavior.

The phase behavior and matrix dynamics of amorphous blends of octenyl succinic anhydride (OSA) modified starch and sucrose was studied as function of blend composition and water content. Phase separation into two amorphous phases, one enriched in OSA starch and the other in sucrose, was confirmed by differential scanning calorimetry (DSC). DSC and 1H solid-state NMR show that the phase separation is only partial. The glass transition temperature (Tg) of the OSA starch-rich phase was found to be ∼30-100 K higher than the Tg of the sucrose-rich phase, depending on blend composition and water content. A novel type of coupling between changes in physical state of the sucrose-rich phase and plasticizer redistribution is proposed, leading to an unexpected increase of the glass transition temperature of the modified starch-rich phase at higher matrix water contents. A quantitative model for the phase separation of the anhydrous blends into two amorphous phases is presented. The model predicts that, with increasing blend sucrose content, the weight fraction of the sucrose-rich phase decreases, while the sucrose content of both the OSA starch-rich phase and the sucrose-rich phase increases. This novel phenomenon is relevant in the understanding of the stability and performance of multiphase food and pharmaceutical components.

Influence of surfactant composition on physical and oxidative stability of Quillaja saponin-stabilized lipid particles with encapsulated ω-3 fish oil.

The purpose of this study was to investigate the potential of a saponin-rich extract of Quillaja saponaria to replace bile salts in the surfactant formulations for stabilization of nanostructured lipid carriers (NLC). The influence of Quillaja extract and/or high-melting lecithin at different concentrations on physical and oxidative stability was evaluated in (i) NLC containing tristearin and ω-3 fish oil, (ii) ω-3 fish oil-in-water emulsion, and (iii) solid lipid nanoparticles (SLN) containing tristearin. Best physical, polymorphic and oxidative stability of NLC were achieved with a surfactant combination of 2.4% (w/w) Quillaja extract and 0.6% (w/w) high-melting lecithin. The results showed that encapsulation of ω-3 fish oil into NLC inhibited the formation of lipid hydroperoxides, propanal and hexanal by 72, 53 and 57%, respectively, compared to the fish oil-in-water emulsion prepared with the same surfactants. This indicated that the low oxidation observed in NLC cannot be due to potential antioxidative effects of the surfactant combination itself. Evidence is accumulating that tristearin is able to form a protective shell around the ω-3 fish oil, when crystallization is induced via high-melting phospholipids in the solidified interfacial layer.

Engineering of layer-by-layer coated capsules with the prospect of materials for efficient and directed electron transfer.

Intermolecular electron transfer is investigated in a dye-doped polyelectrolyte (PE) multilayer film. Hollow PE capsules, with a mean diameter of 2 microm, were prepared by stepwise adsorption of a pyrene (PY)-labeled polyanion and various polycations onto charged colloids and subsequent dissolution of the colloidal core. The high concentration of dye molecules within the capsule wall and the control of the medium polarity on a nanometer length scale are proposed to facilitate light-induced charge separation over distances of a few nanometers. In particular, a PY-labeled poly(styrene sulfonate) (PSS-PY) has been synthesized and used as polyanion for the polyelectrolyte capsule preparation. A polarity gradient across the wall of the PE shells is assumed to be achieved by adsorbing diverse polycations at different film positions. The high effective film area followed by high optical density of the PE capsule solution enables time-resolved optical spectroscopy. Using pulsed excited state absorption (ESA) the transient absorption peaks of the radical anion and cation state of pyrene were measured, respectively. In the presence of additional electron donor (or acceptor) molecules in the capsule solution the pyrene anion (cation) is observed in the ESA spectra, while both transient states are seen if no additional molecules are present. These results are interpreted as an electron transfer from pyrene to the donor (acceptor) molecule or between two pyrene molecules. An asymmetry of the electron donor and electron acceptor efficiency was observed when multilayer shells were used that are supposed to carry an internal polarity gradient.