Plant-Based Colloidal Delivery Systems for Bioactives

The supplementation of plant-based foods and beverages with bioactive agents may be an important strategy for increasing human healthiness. Numerous kinds of colloidal delivery systems have been developed to encapsulate bioactives with the goal of improving their water dispersibility, chemical stability, and bioavailability. In this review, we focus on colloidal delivery systems assembled entirely from plant-based ingredients, such as lipids, proteins, polysaccharides, phospholipids, and surfactants isolated from botanical sources. In particular, the utilization of these ingredients to create plant-based nanoemulsions, nanoliposomes, nanoparticles, and microgels is covered. The utilization of these delivery systems to encapsulate, protect, and release various kinds of bioactives is highlighted, including oil-soluble vitamins (like vitamin D), ω-3 oils, carotenoids (vitamin A precursors), curcuminoids, and polyphenols. The functionality of these delivery systems can be tailored to specific applications by careful selection of ingredients and processing operations, as this enables the composition, size, shape, internal structure, surface chemistry, and electrical characteristics of the colloidal particles to be controlled. The plant-based delivery systems discussed in this article may be useful for introducing active ingredients into the next generation of plant-based foods, meat, seafood, milk, and egg analogs. Nevertheless, there is still a need to systematically compare the functional performance of different delivery systems for specific applications to establish the most appropriate one. In addition, there is a need to test their efficacy at delivering bioavailable forms of bioactives using in vivo studies.     

Emulsification using micro porous glass (MPG): surface behaviour of milk proteins

To investigate the emulsifying properties and adsorption behaviour of high molecular amphiphilic substances such as proteins, it is important to maintain the native status of the used samples. The new method of micro porous glass (MPG) emulsification could offer an opportunity to do this because of the low shear forces. The oil-in-water emulsions were produced by dispersing the hydrophobic phase (liquid butter fat or sunflower oil) through the MPG of different average pore diameters (d_p=0.2 or 0.5 μm) into the flowing continuous phase containing the milk proteins (from reconstituted skim milk and buttermilk). The emulsions were characterised by particle size distribution, creaming behaviour and protein adsorption at the hydrophobic phase. The particle size distribution of protein-stabilised MPG emulsions is determined by the pore size of MPG, the velocity of continuous phase (or wall shear stress σ_w) and the transmembrane pressure. A high velocity of =2 m s⁻¹ (σ_w=13.4 Pa) and low pressure (pressure of disperse phase slightly exceeded the critical pressure Δp_TM=4.5 bar of 0.2 μm-MPG) led to the smallest droplet diameter. As a consequence of average droplet diameters of d₄₃>3.5 μm creaming was observed without centrifugation in all MPG emulsions after 24 h, but no coalescence of the oil droplets occurred. The study of protein adsorption showed that the MPG emulsification at low shear forces resulted in lower protein load values (2.5±0.5 mg m⁻²) than pressure emulsification (11.5±1.0 mg m⁻²). In addition, the various emulsification conditions (MPG or pressure homogenization) led to differences in the relative proportions of casein fractions, whey proteins and milk fat globule membranes (MFGM) at the fat globule surfaces.     

A chiral axial next nearest neighbour xy-model for antiferroelectric liquid crystals

We describe a chiral axial next nearest neighbour xy-model to account for the various subphases exhibited by antiferroelectric liquid crystals made of chiral rod-like molecules. The assumed form of the interlayer interactions is based on physical processes which are discussed. Using a discrete model, the predicted sequence of transitions is SmA-SmC-SmC-FI_H-FI_I-FI_L-SmC ^* A, where FI stands for a ferriphase, as seen in many compounds. The ferri and SmC phases are characterized by relatively large angles between the c-vectors of successive layers and occur only when the compounds have high optical purity. The calculated field induced structures exhibit a plateau of the apparent tilt angle at , where is the tilt angle of the molecules in the ferriphase. The conoscopic figures in the presence of a field and ellipsometric parameters in the absence of a field have also been generated, which agree extremely well with the experimental results. Recent anomalous X-ray scattering studies prove the xy-character of the configurations, though the commensurate structures that are found in the ferriphase require an extension of the model to include lock-in terms. Received 23 August 1999     

Solubility of highly charged anionic polyelectrolytes in presence of multivalent cations: Specific interaction effect

Studies performed on strong polyelectrolytes and on a weak polyelectrolyte, sodium poly(acrylate), show that their stability in presence of multivalent cations depends on the chemical nature of the charged side groups of the polymer. For sulfonate groups (SO₃ ^-) or sulfate groups (OSO₃ ^-) phase separation generally occurs in presence of inorganic cations of valency 3 (as La³⁺) or larger and a resolubilization takes place at high salt concentration. The interactions of the polyelectrolyte with multivalent cations are of electrostatic origin and the phase diagrams are weakly dependent on the chemical nature of the polymer backbone and on the specificity of the counterions. For acrylate groups, (COO^-), the phase separation was observed with inorganic cations of valency 2 (as Ca²⁺) or larger without resolubilization at high salt concentration. The phase separation is due to a chemical association between cations and acrylate groups of two neighboring monomers of the same chain. This chemical association creates a hydrophobic complex by dehydrating both monomer and cation. With organic trivalent cation, as spermidine ⁺H₃N(CH₂)₄NH₂ ⁺(CH₂)₃NH₃ ⁺, where no chemical association occurs with the charged side groups COO^- or SO₃ ^- of the polyelectrolyte, similar phase diagrams were observed whatever was the polyelectrolyte with a resolubilization at high trivalent cation concentration. Received 3 March 1999 and Received in final form 2 September 1999     

Droplet coalescence in the shear flow of model emulsions

During the flow of an emulsion, droplets of the dispersed phase can deform, break up, coalesce or migrate to other regions within the flow field. Understanding these different processes is relevant to morphology development in immiscible polymer blends. Here, emulsions of castor oil in silicone oil were employed to study shear-induced coalescence alone; the conditions chosen were such that drop breakup and drop migration did not occur. A cone-and-plate device and tubes of varying length were used to examine the influence of the average shear rate, the time of shearing, concentration of the dispersed phase, and temperature on the average droplet size. It was found that the extent of “demixing” was not influenced by the spatially non-homogeneous nature of flow in a tube; results correlated very well with the average shear rate. On the other hand, coalescence was significant even when the concentration of the dispersed phase was as low as 0.5%, and it became more important as the concentration was increased. Other results were that the extent of coalescence could be promoted by lowering the shear rate. In quantitative terms, it was found that available coalescence theory gave the correct order of magnitude for the average steady-state droplet size as a function of the imposed shear rate, but the actual variation of drop size with shear rate was gentler than that predicted by theory. An unusual observation was that, under some circumstances, the droplets did not coalesce but simply stuck to each other and maintained their separate identity. Received: 25 March 1999/Accepted: 22 July 1999     

Water droplets in a spherically confined nematic solvent: A numerical investigation

Recently, it was observed that water droplets suspended in a nematic liquid crystal form linear chains [Poulin et al., Science 275, 1770 (1997)]. The chaining occurs, e.g., in a large nematic drop with homeotropic boundary conditions at all the surfaces. Between each pair of water droplets a point defect in the liquid crystalline order was found in accordance with topological constraints. This point defect causes a repulsion between the water droplets. In our numerical investigation we limit ourselves to a chain of two droplets. For such a complex geometry we use the method of finite elements to minimize the Frank free energy. We confirm an experimental observation that the distance d of the point defect from the surface of a water droplet scales with the radius r of the droplet like .When the water droplets are moved apart, we find that the point defect does not stay in the middle between the droplets, but rather forms a dipole with one of them. This confirms a theoretical model for the chaining. Analogies to a second order phase transition are drawn. We also find the dipole when one water droplet is suspended in a bipolar nematic drop with two boojums, i.e., surface defects at the outer boundary. Finally, we present a configuration where two droplets repel each other without a defect between them. Received 11 December 1998     

Pickering乳液在功能高分子材料研究中的应用

功能高分子材料制备的瓶颈问题是如何解决多重材料的相容性问题,传统的物理共混技术和聚合添加技术无法保证材料的稳定性及均一性。 Pickering乳液具有成本低、毒性小、环境友好、稳定性好、制备的多重材料结构稳定等优点,在制备功能高分子材料的应用中越来越受到人们的重视。 本文详细介绍了Pickering乳液在功能性高分子材料制备中的应用研究进展,提出了Pickering乳液聚合制备功能高分子材料面临的一些问题,并结合本课题组的研究方向,对其发展前景进行了展望。     

疏水缔合聚合物稳定乳状液的研究*

本文综述了近年来疏水缔合聚合物稳定乳状液的研究进展。论述了疏水缔合聚合物水溶液的性质,由于其较复杂的分子结构以及其分子主链上疏水基团的缔合作用,使其水溶液增稠的能力比小分子表面活性剂的增稠能力强的多。另外,对疏水缔合聚合物单独稳定乳状液的研究现状进行了介绍,其稳定乳状液的机理与小分子表面活性剂不同。同时讨论了疏水缔合聚合物与表面活性剂的相互作用,此类聚合物可与小分子表面活性剂通过静电和疏水缔合发生强烈的相互作用形成复合体系,并评述了其复配体系稳定乳状液的情况。最后总结了疏水缔合聚合物稳定乳状液的机理。     

Polyoxyalkylenated amines for breaking water-in-oil emulsions: effect of structural variations on the demulsification efficiency

In the present work, different aliphatic and aromatic amines were ethoxylated after a previous propoxylation (PPPEA) with different degrees of propoxylation and ethoxylation in order to obtain polymeric surfactants having different hydrophilic–lipophilic balance (HLB) values. The influence of the structural variations in the prepared PPPEA on their efficiency as demulsifiers for water-in-oil emulsions was investigated. Synthetic water-in-benzene emulsions stabilized by petroleum asphaltenes was utilized for the completion of this study. The actual propylene oxide (PO)–ethylene oxide (EO) ratios of the PPPEA under investigation was elucidated via ¹H NMR spectroscopy. It was found that each demulsifier practices a maximum demulsification efficiency at an optimum concentration. At this concentration, the demulsifiers’ molecules were believed to form a monolayer by adsorbance at the benzene–water interface. The influences of the number of aromatic rings in the molecule, the degree of substitution in the aromatic rings, the number of amine groups, the number of PO–EO chains and HLB on the demulsification efficiency were accomplished. © 1998 John Wiley & Sons, Ltd.     

基于离聚体的自乳化型水基微乳液研究进展

：本文对近几十年来的以离聚体为基的两亲型高聚物水基微乳液的研究状况进行了综述，介绍了这类方法的特点，总结了影响相反转因素、影响微乳液性质的因素等。对水基微乳液的性能和应用前景等也作了简要介绍。