Evidence and characterization of complex coacervates containing plant proteins: application to the microencapsulation of oil droplets

Proteins, polysaccharides, and their complexes used as stabilizers for emulsions: alternatives to synthetic surfactants in the pharmaceutical field?

Emulsions are widely used in pharmaceutics for the encapsulation, solubilization, entrapment, and controlled delivery of active ingredients. In order to answer the increasing demand for clean label excipients, natural polymers can replace the potentially irritative synthetic surfactants used in emulsion formulation. Indeed, biopolymers are currently used in the food industry to stabilize emulsions, and they appear as promising candidates in the pharmaceutical field too. All proteins and some polysaccharides are able to adsorb at a globule surface, thus decreasing the interfacial tension and enhancing the interfacial elasticity. However, most polysaccharides stabilize emulsions simply by increasing the viscosity of the continuous phase. Proteins and polysaccharides may also be associated either through covalent bonding or electrostatic interactions. The combination of the properties of these biopolymers under appropriate conditions leads to increased emulsion stability. Alternative layers of oppositely charged biopolymers can also be formed around the globules to obtain multi-layered "membranes". These layers can provide electrostatic and steric stabilization thus improving thermal stability and resistance to external treatment. The novel biopolymer-stabilized emulsions have a great potential in the pharmaceutical field for encapsulation, controlled digestion, and targeted release although several challenging issues such as storage and bacteriological concerns still need to be addressed.

Complex coacervation of collagen hydrolysate extracted from leather solid wastes and chitosan for controlled release of lavender oil

In the world, approximately 600,000 metric tonnes of chromium-containing solid wastes are generated by the leather industry each year. Environmental concerns and escalating landfill costs are becoming increasingly serious problems to the leather industry and seeking solutions to these problems is a prime concern in much research today. In this study, solid collagen-based protein hydrolysate was isolated from chromium-tanned leather wastes and its chemical properties were determined. Microcapsules of collagen hydrolysate (CH) - chitosan (C) crosslinked with glutaraldehyde (GA) containing Lavender oil (LO) were prepared by complex coacervation method. The effects of various processing parameters, including the CH to C ratio, LO content, and GA, on the oil load (%), oil content (%), encapsulation efficiency (%) and release rate of LO from microcapsules were investigated. As the ratio of C present in the CH/C mixture and crosslinking density increased, the release rate of LO from microcapsules slowed down. Optical and scanning electron microscopy images illustrated that the LO microcapsules were spherical in shape. Fourier transform infrared spectroscopy (FTIR) studies confirmed that there was no significant interaction between CH/C complex and LO.

Effect of orange peel essential oil on oxidative stress in AOM animals

The processing parameters of pump speed, inlet air temperature, outlet air temperature and homogenization pressure were evaluated. Encapsulation efficiency is high with a satisfied releasing rate. Then, acute otitis media (AOM) animal model was built and diet containing orange peel essential oil microcapsules were administrated to AOM animals. Pharmacological test showed that orange peel essential oil treatment could decrease serum and cochlea malondialdehyde (MDA), immunoglobulins A (IgA), immunoglobulins G (IgG), immunoglobulins M (IgM) levels and increase antioxidant enzymes activities. It can be concluded that orange peel essential oil treatment could decrease oxidative injury in acute otitis media rats.

Protein/polysaccharide complexes and coacervates in food systems

Since the pioneering work of Bungenberg de Jong and co-workers on gelatin-acacia gum complex coacervation in the 1920-40s, protein/polysaccharide complexes and coacervates have received increasing research interest in order to broaden the possible food applications. This review focuses on the main research streams followed in this field during the last 12 years regarding: i) the parameters influencing the formation of complexes and coacervates in protein-polysaccharide systems; ii) the characterization of the kinetics of phase separation and multi-scale structure of the complexes and coacervates; and iii) the investigation of the functional properties of complexes and coacervates in food applications. This latter section encompasses various technological aspects, namely: the viscosifying and gelling ability, the foaming and emulsifying ability and finally, the stabilization and release of bioactives or sensitive compounds.

The adhesive properties of coacervated recombinant hybrid mussel adhesive proteins

Marine mussels attach to substrates using adhesive proteins. It has been suggested that complex coacervation (liquid-liquid phase separation via concentration) might be involved in the highly condensed and non-water dispersed adhesion process of mussel adhesive proteins (MAPs). However, as purified natural MAPs are difficult to obtain, it has not been possible to experimentally validate the coacervation model. In the present work, we demonstrate complex coacervation in a system including recombinant MAPs and hyaluronic acid (HA). Our recombinant hybrid MAPs, fp-151 and fp-131, can be produced in large quantities, and are readily purified. We observed successful complex coacervation using cationic fp-151 or fp-131, and an anionic HA partner. Importantly, we found that highly condensed complex coacervates significantly increased the bulk adhesive strength of MAPs in both dry and wet environments. In addition, oil droplets were successfully engulfed using a MAP-based interfacial coacervation process, to form microencapsulated particles. Collectively, our results indicate that a complex coacervation system based on MAPs shows superior adhesive properties, combined with additional valuable features including liquid/liquid phase separation and appropriate viscoelasticity. Our microencapsulation system could be useful in the development of new adhesive biomaterials, including self-adhesive microencapsulated drug carriers, for use in biotechnological and biomedical applications.

Intermolecular interactions during complex coacervation of pea protein isolate and gum arabic

The nature of intermolecular interactions during complexation between pea protein isolate (PPI) and gum arabic (GA) was investigated as a function of pH (4.30-2.40) by turbidimetric analysis and confocal scanning microscopy in the presence of destabilizing agents (100 mM NaCl or 100 mM urea) and at different temperatures (6-60 degrees C). Complex formation followed two pH-dependent structure-forming events associated with the formation of soluble and insoluble complexes and involved interactions between GA and PPI aggregates. Complex formation was driven by electrostatic attractive forces between complementary charged biopolymers, with secondary stabilization by hydrogen bonding. Hydrophobic interactions were found to enhance complex stability at lower pH (pH 3.10), but not with its formation.

1H NMR relaxation studies of protein-polysaccharide mixtures

NMR water proton relaxation was used to characterize the structure of plant proteins and plant protein-polysaccharide mixtures in aqueous solutions. The method is based on the mobility determination of the water molecules in the biopolymer environment in solutions through relaxation time measurements. Differences of conformation between pea globulin and alpha gliadin seem to control the water molecules mobility in their environment. As deduced from the study of complexes, the electrostatic interactions may also play a major role in the water molecule motions. The phase separation induced under specific conditions seems to promote the translational diffusion of structured water molecules whereas the rotational motion was more restricted.

Mesophase separation and probe dynamics in protein-polyelectrolyte coacervates

Protein-polyelectrolyte coacervates are self-assembling macroscopically monophasic biomacromolecular fluids whose unique properties arise from transient heterogeneities. The structures of coacervates formed at different conditions of pH and ionic strength from poly(dimethyldiallylammonium chloride) and bovine serum albumin (BSA), were probed using fluorescence recovery after photobleaching. Measurements of self-diffusion in coacervates were carried out using fluorescein-tagged BSA, and similarly tagged Ficoll, a non-interacting branched polysaccharide with the same size as BSA. The results are best explained by temporal and spatial heterogeneities, also inferred from static light scattering and cryo-TEM, which indicate heterogeneous scattering centers of several hundred nm. Taken together with previous dynamic light scattering and rheology studies, the results are consistent with the presence of extensive dilute domains in which are embedded partially interconnected 50-700 nm dense domains. At short length scales, protein mobility is unobstructed by these clusters. At intermediate length scales, proteins are slowed down due to tortuosity effects within the blind alleys of the dense domains, and to adsorption at dense/dilute domain interfaces. Finally, at long length scales, obstructed diffusion is alleviated by the break-up of dense domains. These findings are discussed in terms of previously suggested models for protein-polyelectrolyte coacervates. Possible explanations for the origin of mesophase separation are offered.

Conformational Modifications of α Gliadin and Globulin Proteins upon Complex Coacervates Formation with Gum Arabic as Studied by Raman Microspectroscopy

As a molecular model of gelatin-free coacervates, complexes of pea globulin and alpha gliadin proteins with gum arabic prepared at different acidic pH values are studied using Raman microspectrometry. Raman spectra confirm higher content of beta-sheets and random coils in pea globulin and dominating alpha-helical structures in alpha gliadin. For protein-gum arabic complexes, Raman data support the existence of specific pH conditions for optimal complex coacervation (pH 2.75 for globulin and pH 3.0 for gliadin(1)), when (i) pH-induced conformational perturbations of free protein structure are the strongest and (ii) compensation of these perturbations by gum arabic is the most pronounced. Conformations implied in the protein-gum complexes are mainly beta-sheets in pea globulin and alpha-helix in alpha gliadin. The role of electrostatic and non-Coulombic interactions (intermolecular hydrogen bonds) in stabilizing of protein-polysaccharide complexes is discussed in relation with the overall structure and the charge density profile of these two proteins.

Ibuprofen-loaded nanoparticles prepared by a co-precipitation method and their release properties

A co-precipitation method was established to fabricate nano-scale core-shell particles, by which poor water-soluble drugs can be effectively dispersed with rather good stability during storage. Exemplified with formation of ibuprofen (Ib) nanoparticles stabilized by DEAE dextran (Ddex), the process includes precipitation of Ib in a supersaturated solution and deposition of Ddex onto the precipitated Ib particles through electrostatic interaction. Characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and zeta potential, the core-shell structure of the particles formed at pH 6.0 with a Ddex/Ib weight ratio of 5:1 was identified with Ib being the core and Ddex being the shell. As a comparison, particles formed at other pH values and other Ddex/Ib ratios were also studied. Along with increase of the Ddex/Ib ratio or pH value of the final aqueous solution, the particle size was decreased, demonstrating that the particle sizes could be readily tuned by variation of the fabrication parameters. At conditions that the Ib concentration was lower than its supersaturated value, for example at higher pH value, instead of co-precipitation mechanism, forces such as electrostatic complexation dominate the formation of Ddex-Ib particles. Moreover, drug entrapment was mainly dependent on the Ib solubility regardless of the ratio between Ddex and Ib, while the drug content was decreased as a function of Ddex/Ib ratio. In vitro release studies showed that the loaded Ib could be again released in a burst manner during the initial stage, followed with a slow rate. The final released amount of Ib showed a positive correlation with the bulk pH value, e.g. approximately 60, 80 and 90% of the loaded Ib were released in pH 1.0, 5.8 and 7.4 buffered solutions after incubation for 40 h, respectively.

Plant protein-polysaccharide interactions in solutions: application of soft particle analysis and light scattering measurements

The soft particle analysis theory was applied to plant proteins and polysaccharides in solution, to determine the charge density of these polymers and the depth of the layer accessible by counterions according to pH conditions. In addition to the macromolecule shape characterized by light scattering measurements, these properties are also correlated with the optimum coacervation condition, so as to establish the prevalent plant protein-polysaccharide interactions governing the coacervate formation. Globulin was found to be highly charged and spherically shaped. The best coacervation condition was obtained at the pH value, which corresponds to the protein conformation with a dense and compact accessible layer. On the contrary, for the alpha gliadin, bearing a lower charge, a more extended conformation seems to be more favourable. For the plant proteins studied, the coacervation seems to be controlled by the structure of the counter polyanion used: from our model, it turns out that the rod-like structure of arabic gum observed at acidic pH allows the interaction with plant proteins to form coacervates, contrary to the highly charged and spherical structure of alginate.