Nissim Garti

Double emulsions : scope, limitations and new achievements

Abstract Multiple emulsions are complex systems, termed “emulsions of emulsions”, i.e. the droplets of the dispersed phase contain even smaller dispersed droplets themselves. Each dispersed globule in the double emulsion is separated from the aqueous phase by a layer of oil-phase compartments. Double emulsions have significant potential in many applications since, at least in theory, they can serve as an entrapping reservoir for active ingredients that can be released from the inner phase to the outer phase by a controlled and a sustained mechanism. Many of the potential applications are in pharmaceuticals. In practice, double emulsions are thermodynamically unstable systems with a strong tendency for coalescence, flocculation and creaming. Most double emulsions consist of relatively large droplets, cannot withstand storage regimes and have a strong tendency to release the entrapped matter in an uncontrolled manner. Much work has been devoted in the last decade in order to the improve the stability of the multiple emulsions and the control of the release rates of the addenda. The most recent achievements are: Use of polymeric emulsifiers to improve interface coverage and to better anchor into the dispersed phases; Reduce droplets size by improving methods of formation: improved understanding of the release mechanisms and use of various additives to control the release via the reverse micellar mechanism.

Protein-Polysaccharide Interactions for Stabilization of Food Emulsions

ABSTRACT Proteins, polysaccharides and their blends, as examples of natural biopolymers, are surface active materials. Biopolymers may be considered as amphiphilic macromolecules that play an essential role in stabilizing food formulations (foams, emulsions and dispersions). Under specific conditions (such as protein-to-polysaccharide ratio, pH, ionic strength, temperature, mixing processing), it has been stated that proteins and polysaccharides form hybrids (complexes) with enhanced functional properties in comparison to the proteins and polysaccharides alone. Different protein-polysaccharide pairs are reviewed with particular attention to the emulsification capability of their mixtures. In the case of uncomplexed blends of biopolymers, competitive adsorption onto hydrophobic surfaces is generally reported. Conversely, electrostatic complexation between oppositely charged proteins and polysaccharides allows better anchoring of the new-formed macro-molecular amphiphile onto oil-water interfaces. Moreover, improved thermal stability and increased resistance to external treatment (high pressure) involved in food processing are obtained. This review presents basic and applied knowledge on protein-polysaccharide interactions in aqueous medium and at the oil-water interface in food emulsion systems. Electrostatic interactions and thermodynamic incompatibility in mixed biopolymer solutions are correlated to the functional properties (rheology, surface hydrophobiciry, emulsification power) of these interesting blends. Basic and industrial selected systems of different families of hydrocolloids (as gum Arabic, galactomannans, pectins) and protein (caseins, whey, soya, gelatin) mixtures are reviewed.

Double emulsions: Progress and applications

Research work and progress on several major issues related to double emulsions have taken place recently. Such developments include the intrinsic thermodynamic instability derived from the droplets size of the double emulsion; how the release of active ingredients entrapped within the inner phase can be prolonged and controlled; new advanced methods for investigating the structure and nature of double emulsion droplets and their interfaces; new possible applications of double emulsions for sustained and prolonged release of active ingredients in cosmetics, food, agriculture and pharmaceuticals; double emulsions as intermediate systems in the preparation of microspheres or nanospheres; and the scope and limitations of possible new applications of multicompartment microspheres prepared from double emulsions.

Phase behavior of microemulsions based on food-grade nonionic surfactants: effect of polyols and short-chain alcohols ☆

Abstract The improved water and oil solubilization in the presence of polyols (propylene glycol, PG, and glycerol, Gly) and short-chain alcohol (ethanol) in U-type nonionic W/O and O/W food microemulsions was investigated. The phase behavior of systems based on Tweens (ethoxylated sorbitan esters) was compared with non-food-grade systems based on C18:1E10 (Brij 96v). Short-chain alcohol (ethanol in food-grade systems) together with polyols (glycerol and propylene glycol) when added to a three component system (oil–surfactant–water) induce the formation of both water-in-oil (W/O) and oil-in-water (O/W) microemulsions. Alcohols and polyols destabilize the liquid crystalline phase and extend the isotropic region to higher surfactant concentrations. The total monophasic area, AT, at R(+)-limonene/ethanol of 1/1 (w/w) and aqueous phase of water/PG of 1/1 (w/w), was 73 and 64% of the total area of the phase diagram for Brij 96v and Tween 60, respectively. The transition from a W/O microemulsion into an O/W microemulsion happens gradually, and continuously without any phase separation. The total monophasic area depends also on the type of the oil, on the composition of the polar and apolar phases, and on the nature of the polyol. The results are discussed in terms of BSO equation, spontaneous curvature, H0, film flexibility, κ and κ , surfactant oil and surfactant cosolvent compatibility and the participation of the polyol at the interface. The difference in temperature sensitivity of PG-based microemulsions vs. temperature sensitivity of Gly-based is demonstrated and explained.

Crystallization processes in fats and lipid systems

Crystallization processes polymorphism and phase transitions of fatty acids and acylglycerols morphological connected net roughening transition theory - application to beta-2 crystals of triaclglycerols nucleation and growth in the solid-solid phase transitions of n-alkanes molecular interactions and phase behaviour of polymorphic fats the roles of emulsifiers in fat crystallization crystallization of oil-in-water emulsions fat crystal networks lipid crystallization and its effect on the physical structure of ice cream crystallization of palm oil and its fractions advances in milk fat fractionation - technology and applications crystallization properties of cocoa butter influences of colloidal state on physical properties of solid fats separation and crystallization of oleaginous constituents in cosmetics - sweating and blooming crystallization properties and lyotropic phase behaviour of food emulsifiers - relation to applications.

Double emulsions stabilized by macromolecular surfactants

Abstract Multiple emulsions are emulsions within emulsions, stabilized traditionally by monomeric emulsifiers both at the inner and outer interface. Double emulsions are thermodynamically unstable and fast coalescence, as well as fast release of markers and drugs, have been the main drawbacks of this technology. Polymeric synthetic emulsifiers, as well as natural macromolecules in combination with monomeric emulsifiers, have recently been studied and evaluated. The review brings new results on the use of amphiphilic proteins such as BSA and casein along with monomeric emulsifiers in relation to improved stability and release properties. Kinetic results are brought to demonstrate the role of BSA as the inner emulsifier and the outer emulsifier. Diffusion controlled mechanisms are suggested. Synthetic block copolymers based on silicon backbones and polyethylene oxide side-chains have also been studied. Double emulsions with relatively small droplets (5 μm) are formed and excellent stability (to storage, sheer and dilution) is obtained. Release data indicates that the newly designed double emulsions have longer shelf-life and very slow rates of release of markers. Such emulsions are good candidates for agricultural formulations.

What can nature offer from an emulsifier point of view: trends and progress?

Abstract The most complex emulsions are those of foods and, therefore, are difficult to stabilize. An infinite number of microstructures of combinations of proteins, carbohydrates, fats and lipids are present in food systems. There is an increasing awareness of many investigators to the relevance of the principles of colloid and surface science to many of the technological problems related to advanced foods. Amphiphilic molecules play a key role in the stabilization of many of the food colloids. It is, therefore, very important to understand the interfacial behaviour of these molecules and to select the proper ones for the proper activity. Synthetic surfactants and emulsifiers are widely used in many of our foods, but, it becomes very important to replace them by natural molecules with good health records. The following review discusses the main natural ocurring molecules that are in use today and the future trends in this area. Monomeric emulsifiers such as mono and mono-diglycerides, lecithins and lysolecithins are still key players. Glycolipids are present only in very minor concentrations in plants and animals and therefore are not commercially available. Saponins are a very interesting group of materials with increasing potential. The polymeric amphiphilic compounds are “native” and enzymatically modified proteins. However, in situ products chemically modified by a Maillard reaction can also be used as emulsifiers. The most interesting new emulsifiers are some selected hydrocolloids that exhibit surface properties and emulsification capabilities. Enzymatically modified hydrocolloids show significant promise. Biosurfactants have also been studied and considered as emulsifiers, but are not food grade products. New trends and progress will also be discussed.

HYDROCOLLOIDS AS EMULSIFYING AGENTS FOR OIL-IN-WATER EMULSIONS

Abstract Hydrocolloids are water-soluble biopolymers consisting of high molecular weight polysaccharides. For generations, these biopolymers were also termed gums or stabilizers imparting viscosity, gelification and long-term stability to food systems. Some hydrocolloids were also considered as emulsifying agents, since they help to form and stabilize oil-in-water emulsions. Only in the last two decades questions have been raised as to the mode of their action in low viscosity and low concentrations dispersed systems consisting of oil and water. Gum Arabic is the only gum in use in dilute emulsion systems which was proved to be a good emulsifier - adsorbing onto oil-water interfaces and imparting steric stabilization. However, other gums have been known to reduce surface and interfacial tensions, to adsorb onto solid surfaces and to improve stability of oil-in-water emulsions. Only recently attention has been paid to the structure-surface activity relationship between the gums and their emulsification abi...

Microemulsions as microreactors for food applications

Major recent advances. Structured self-assembled liquids have been considered as efficient microreactors for organic and enzymatic reactions. Only recently scientists learned to use food-grade cosolvents and coemulsifiers together with hydrophilic non-ionic surfactants and to construct U-type phase diagrams with large isotropic regions ranging continuously from the oil-rich corner to the water-rich corner without any phase separation. The U-type microemulsions facilitate triggering and control of certain reactions by changing water activities. Maillard thermal degradation between sugars and amino acids is the main, and almost the only, chemical reaction that has been studied in food-grade microemulsions. Some examples of recent studies include: Maillard processes in binary structured fluids composed of monoglycerides of fatty acids and water forming microemulsions and lyotropic liquid crystalline structures; pseudoternary and pseudoquaternary W/O microemulsions; U-type microemulsions (W/O, O/W and bicontinuous microemulsions); enzymatic reactions aimed to prepare other surfactants such as sugar esters, monoglycerides and lysolecithins or triglycerides. Reactions in microreactors lead to unique new products. The reaction products and rates are controlled by the hydrophilicity/lipophilicity of the reagents (guest molecules), their molar ratios, type of oil phase, nature of surfactants and oil/surfactant ratios, nature of curvature and its elasticity (adjusted by cosolvent and coemulsifier) and by the water activity. The field is in its infancy and will need work of many more model reactions before it will be used in industrial food applications. Enzymatic reactions in non-food microemulsions are common practice but only few examples of food microemulsions as enzymatic microreactors have been extensively studied.

A DSC study of water behavior in water-in-oil microemulsions stabilized by sucrose esters and butanol

Abstract Sub-zero temperature differential scanning calorimetry (SZT-DSC) has been applied to a model nonionic water-in-oil microemulsion system based on: sucrose esters/water/1-butanol/ n -alkanes (C 12 –C 16 ). The maximum water solubilization was 40, 56 and 80 wt.% for the systems containing n -dodecane, n -tetradecane and n -hexadecane as the oil phase, respectively. Two types of solubilized water have been detected. The so-called ‘bulk’ (free) water present in the core of the microemulsion and the ‘interfacial’ (bound) water attached at the interface to the surfactant (and/or butanol). The internal distribution of the water within the microemulsions was determined along two dilution lines (with 32 and 43 wt.% of the initial surfactant). It was found that for the n -dodecane system the maximum ‘interfacial’(bound) water is 12 and 14 wt.% along the two dilution lines, respectively. Above this water content a core of ‘bulk’ (free) water is formed. The type of the oil and the butanol interfacial participation strongly affect the water internal distribution. Both the temperature of fusion, T f , of the ‘bulk’ (free) water and of the ‘interfacial’ (bound) water are strongly affected by the butanol and the oil. The nature of the surfactant, its fatty chain length and its HLB also affect the binding capabilities and capacity of water in microemulsion systems. For both n -dodecane and n -hexadecane, 11–13 molecules of water can be bound to the surfactant at the interface.