Emulsions Stabilized by Gum Arabic: Composition and Packing within Interfacial Films

Gum arabic is a heterogeneous natural hydrocolloid commonly used in the agro-food industry to provide metastability to oil-in-water emulsions. Since aqueous solutions of gum arabic contain a complex mixture of protein/polysaccharide conjugates, the composition of interfacial films is expected to differ from the bulk composition. Here, we investigate the composition of interfacial films in oil/water emulsions stabilized by gum arabic at various concentrations, pH and salinity. Using both size exclusion and hydrophobic interaction chromatography separations, we show that the interface is enriched in protein-rich species displaying a broad range of sizes. These species are irreversibly adsorbed as monolayers at the oil/water interface. We observe that the surface coverage density, or packing, of the adsorbed species at oil/water interfaces drastically increases with both the increasing gum concentration and decreasing ionic repulsions, through increasing the ionic strength or decreasing the pH. Strikingly, these packing changes correspond to only minor composition changes in the adsorbed layer. We thus conclude that the key parameter modified in different formulations is the conformation of the adsorbed species rather than their composition distribution. These findings can be readily used to adjust the amount of gum arabic necessary to produce metastable emulsions

Gum Arabic in solution: Composition and multi-scale structures

Gum Arabic is a natural acacia tree exudate containing hyperbranched polysaccharides and proteins. Here, we perform a dual chromatographic separation together with small-angle X-ray and neutron scattering structural characterizations. We show that the different species present in Gum Arabic can not be easily classified in distinct families. They are rather build from various combinations of two building blocks that are evidenced by a mismatch between small-angle X-ray and neutron scattering. One block corresponds to hyperbranched polysaccharides, which we describe as three-dimensional multi-scale porous colloids possessing three length scales of 7, 2 and 0.7 nm. The other block corresponds to protein chains that organize as Gaussian chains in solution and are prone to aggregation. A large array of polysaccharide/protein conjugates was identified, which differs in size, hydrophobicity and amino-acid content. Still, their structure is always the juxtaposition of the two building blocks structures. Additionally, small-angle neutron scattering reveals that large-scale structures are ubiquitous in Gum Arabic solutions and originate from the self-association of both free and conjugated polypeptide chains. Despite its compositional complexity, Gum Arabic solutions thus possess a robust multi-scale structure that is mainly impacted by concentration and ionic repulsions

Effect of tyramine, a dietary amine, on glycerol and lactate release by isolated adipocytes from old rats

Amine degradation by adipocyte amine oxidases leads to the production of metabolites that interact with lipid and glucose metabolisms and their hormonal regulations. To further investigate these interactions, we determined the effect of a dietary amine, tyramine (TYR), on glycerol and lactate releases , respectively taken as indices of lipolytic and glycolytic activities of isolated adipocytes. Old male Wistar rats were used to prepare adipocytes by collagenase dissociation of retroperitoneal fat pads. The two tested doses of tyramine (10 µM and 1 mM) had no effect on basal glycerol release. On the other hand, TYR, at the highest dose tested (1 mM), weakly but significantly increased basal lactate release, which was elevated in adipocytes from old rats. Norepinephrine (NE), highly stimulated adipocyte lipolysis with a submaximal effect at 1 µM which was slightly but significantly inhibited by TYR 1 mM. Insulin 1 nM (INS) also poorly inhibited the NE-stimulated lipolysis in adipocytes isolated from old rats. TYR was able to potentiate the poor antilipolytic efficiency of INS. Under similar conditions, a high dose of NE greatly reduced lactate production and TYR (1 mM) reversed this inhibition of lactate release. INS was also able to totally reverse the inhibitory effect of NE on lactate release, but there was no potentiation between insulin and tyramine effects. It can be concluded that high doses of TYR interact with norepinephrine and insulin, at least on the control of glycerol and lactate release, by counteracting catecholamine effects and by mimicking insulin actions.La degradación de aminas por las amino-oxidasas del tejido adiposo produce metabolitos capaces de influir sobre los metabolismos lipídico y glucídico y su regulación hormonal. Para investigar acerca de estos efectos, se ha estudiado el efecto de la tiramina (TIR), una amina presente en la dieta, sobre la producción de glicerol y de lactato, como índice respectivo de la lipolisis y de la glicolisis. A partir de tejidos adiposo perirrenal de viejos machos de rata Wistar se aislaron adipocitos tras digestión con colagenasa. Se estudió in vitro el efecto de la tiramina a dos concentraciones, 10 µM y 1 mM sobre la liberación de glicerol y de lactato. Ninguna de ellas modificó la liberación basal de glicerol, pero la mayor estimuló la liberación basal de lactato,, ya bastante elevada. La norepinefrina (NE) estimuló fuertemente la lipolisis con un efecto submáximo a 1 µM, que fué inhibido parcial pero significativamente por TIR 1 mM. La producción basal de lactato se redujo por dosis elevadas de NE y esta inhibición se anuló por adición TIR 1 mM. Ademas, la tiramina fue capaz de reforzar la débil acción antilipolítica de la insulina en los adipocitos estimulados por norepinefrina de ratas viejas. Por otra parte, la insulina anuló el efecto inhibidor de la NE sobre la producción basal de lactato sin que se observara potenciación por la presencia de TIR. Estos resultados parecen indicar que la tiramina, a dosis elevadas, puede reemplazar parcialmente el efecto de la insulina e influir sobre el control de la liberación de glicerol y de lactato por la norepinefrina

Emulsions Stabilized by Gum Arabic: How Diversity and Interfacial Networking Lead to Metastability

International audienceGum arabic is a natural hydrocolloid composed of adiversity of amphiphilic species consisting of protein chains covalently linked to multiscale porous polysaccharides. Gum arabic is notably used as a food additive (E414) to provide metastability to oil-in-water emulsions, even after extensive dilution. Here, we investigate the mechanism underlying the emulsion stabilizing properties of gum arabic, using a combination of scattering and chromatographic analyses and the design of a harvesting method to collect adsorbed species. Increasing the interfacial packing of amphiphilic species leads to their irreversible interfacial aggregation, which is driven by hydrophobic interactions between protein chains. This aggregation is promoted by the size diversity of amphiphilic species, with smaller species first aggregating at intermediate interfacial packings, followed by larger species at higher packings. The resulting adsorbed layer can be considered as a shell composed of a two-dimensional protein network, irreversibly cross-linked through hydrophobic interactions, which is covalently linked to hyperbranched polysaccharide chains displaying severe conformational changes compared to their bulk structure. This shell is strongly anchored at the oil−water interface by the protein network and provides steric repulsions through the hydrated polysaccharides. Consequently, if such a shell is adequately formed during emulsification, emulsions stabilized by gum arabic may resist extensive mechanical stresses and display a long-term metastability even after drastic environmental changes. This paves the way toward more rational uses of gum arabic as an emulsion stabilizer in formulations and processes

J Physiol Biochem

Stilbenes are secondary metabolites belonging to the polyphenol family. Those compounds are derived from the glycosylation, prenylation, methoxylation, hydroxylation, or also oligomerization of the well-known trans-resveratrol. One of them, trans-epsilon-viniferin (ε-viniferin), is a trans-resveratrol dimer that arouses the interest of researchers in the field of human health. The biosynthesis of this molecule in various plant species, particularly high in the Vitaceae family, explains its presence in some red wines, which represent the main source of ε-viniferin in the human diet. Although bioavailability studies have shown poor absorption and high metabolism of this stilbene, multiple studies demonstrated its biological properties. The ε-viniferin exhibits strong activities against inflammatory and oxidative stress. Moreover, various studies have reported great activity of this compound not only in a wide range of disorders and diseases, such as cancer, obesity, and its associated disorders, but also in vascular diseases and neurodegeneration, for which the pathophysiology is closely related to the state of oxidation and inflammation. This review provides a state of art of the main activities of ε-viniferin demonstrated in vitro and in vivo, highlighting that this resveratrol dimer could be a promising candidate for future functional foods or supplement foods used for the management of many chronic diseases of concern in terms of public health

<i>Trans</i>-ε-Viniferin Encapsulation in Multi-Lamellar Liposomes: Consequences on Pharmacokinetic Parameters, Biodistribution and Glucuronide Formation in Rats

Trans-ε-viniferin (εVin) is a resveratrol dimer exhibiting promising biological activities for human health. Its bioavailability being low, the development of encapsulation methods would be used to overcome this issue. The aim of this study was to measure the consequences of the encapsulation of εVin in multilamellar liposomes on its pharmacokinetic parameters, metabolism and tissue distribution in rats. After oral administration of εVin (20 mg/kg body weight), either as free or encapsulated forms, plasmas were sequentially collected (from 0 to 4 h) as well as liver, kidneys and adipose tissues (4 h after administration) and analyzed by LC-HRMS. The glucuronide metabolites (εVG) were also produced by hemisynthesis for their quantification in plasma and tissues. The encapsulation process did not significantly modify the pharmacokinetic parameters of εVin itself. However, a significant increase of the T1/2 was noticed for εVG after administration of the encapsulated form as compared to the free form. An accumulation of εVin and εVG in adipose tissues was noticed, and interestingly a significant increase of the latter in the mesenteric one after administration of the encapsulated form was highlighted. Since adipose tissues could represent storage depots, and encapsulation allows for prolonging the exposure time of glucuronide metabolites in the organism, this could be of interest to promote their potential biological activities