Bruno Leuenberger

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.

Influence of encapsulated functional lipids on crystal structure and chemical stability in solid lipid nanoparticles: Towards bioactive-based design of delivery systems

We investigated the influence of physicochemical properties of encapsulated functional lipids--vitamin A, β-carotene and ω-3 fish oil--on the structural arrangement of solid lipid nanoparticles (SLN). The relationship between the crystal structure and chemical stability of the incorporated bioactive lipids was evaluated with different emulsifier compositions of a saponin-rich, food-grade Quillaja extract alone or combined with high-melting or low-melting lecithins. The major factors influencing the structural arrangement and chemical stability of functional lipids in solid lipid dispersions were their solubility in the aqueous phase and their crystallization temperature in relation to that of the carrier lipid. The results showed that the stabilization of the α-subcell crystals in the lattice of the carrier lipid is a key parameter for forming stable solid lipid dispersions. This study contributes to a better understanding of SLN as a function of the bioactive lipid.

Miscibility of Quillaja Saponins with other Co-surfactants under Different pH Values

The miscibility behavior of mixed surfactant systems and the influence of extrinsic parameters are crucial for their application as emulsifiers. Therefore, the objective of this study was to evaluate the miscibility behavior of mixed systems composed of commercial Quillaja saponin and a co-surfactant, namely sodium caseinate, pea protein, rapeseed lecithin, or egg lecithin. These mixtures were evaluated macro- and microscopically at different concentration ratios (maximum concentration 5% w/v) at pH 3, 5, and 7 at 25 °C. The individual ingredients were also assessed for their charge properties and surface hydrophobicity. The results showed that Quillaja saponin-caseinate mixtures were miscible only at pH 7, and showed aggregation and precipitation at lower pH due to increasing electrostatic attraction forces. Rheological measurements showed that Quillaja saponin-pea protein mixtures formed gelled structures at all tested pH values mainly via association of hydrophobic patches. Quillaja saponins mixed with rapeseed lecithin were miscible at all tested pH values due to electrostatic repulsion. Quillaja saponin-egg lecithin mixtures aggregated independent of pH and concentration ratio. The microscopic analysis revealed that the lower the pH and the higher the Quillaja saponin ratio, the denser were the formed Quillaja saponin-egg lecithin aggregates. The results are summarized in ternary phase diagrams that provide a useful tool in selecting a surfactant system for food applications.

Influence of heat on miscibility of Quillaja saponins in mixtures with a co-surfactant

Thermal treatment of mixed surfactant systems can have a major impact on their phase behavior through modified interactions between the surfactants. In this study, we investigated the miscibility behavior of aqueous binary surfactant systems composed of Quillaja saponin extract and sodium caseinate, pea protein, rapeseed lecithin, or egg lecithin at different concentration ratios (0-5% w/v) at pH3, 5, and 7 upon heat treatment (25-75°C). The results revealed that the heat-treated Quillaja saponin-sodium caseinate mixtures at pH7 remained miscible when the ratio of Quillaja saponins was equal or higher to the ratio of caseinate, otherwise the mixtures flocculated due to increased hydrophobic interactions. At pH3, the aggregation of Quillaja saponin-sodium caseinate structures was intensified by heating mainly through self-association of casein molecules. In Quillaja saponin-pea protein mixtures as well as in pure pea protein samples heating led to weakening of the gel structures at all tested pH values. In contrast, heating did not affect Quillaja saponin-rapeseed lecithin mixtures, which stayed miscible independent of pH due to electrostatic repulsive forces. Furthermore, the flocculated (pH5, 7) or aggregated (pH3) Quillaja saponin-egg lecithin mixtures were only slightly affected by heating. These results are important for understanding the interactions of binary surfactant systems when subjected to heating, which is a common processing step in many food applications.

Flow-through cross-polarized imaging as a new tool to overcome the analytical sensitivity challenges of a low-dose crystalline compound in a lipid matrix

Assessing the physical state of a low-dose active compound in a solid lipid or polymer matrix is analytically challenging, especially if the matrix exhibits some crystallinity. The aim of this study was first to compare the ability of current methods to detect the presence of a crystalline model compound in lipid matrices. Subsequently, a new technique was introduced and evaluated because of sensitivity issues that were encountered with current methods. The new technique is a flow-through version of cross-polarized imaging in transmission mode. The tested lipid-based solid dispersions (SDs) consisted of β-carotene (BC) as a model compound, and of Gelucire 50/13 or Geleol mono- and diglycerides as lipid matrices. The solid dispersions were analyzed by (hyper) differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and microscopic techniques including atomic force microscopy (AFM). DSC and XRPD could analyze crystalline BC at concentrations as low as 3% (w/w) in the formulations. However, with microscopic techniques crystalline particles were detected at significantly lower concentrations of even 0.5% (w/w) BC. A flow-through cross-polarized imaging technique was introduced that combines the advantage of analyzing a larger sample size with high sensitivity of microscopy. Crystals were detected easily in samples containing even less than 0.2% (w/w) BC. Moreover, the new tool enabled approximation of the kinetic BC solubility in the crystalline lipid matrices. As a conclusion, the flow-through cross-polarized imaging technique has the potential to become an indispensable tool for characterizing low-dose crystalline compounds in a lipid or polymer matrix of solid dispersions.

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.