Background Considering the global rise of obesity and food-linked cardiovascular diseases, food industries are often challenged to produce low fat or fat-free products. Incorporation of water in the form of water-in-oil (W/O) emulsions to replace fat offers a promising strategy to address this research challenge. Scope and approach This review aims to provide succinct insights into the stabilization of W/O emulsions, focusing on interfacial design using surfactants, biopolymers, particles and/or combinations thereof that have been researched in the last decade. Particular emphasis has been given to particle (Pickering) stabilization of water droplets with bio-derived as well as non-bio-derived particles. In addition, the stabilization of W/O emulsions via viscosity modification is also briefly examined. Key findings and conclusions Although polyglycerol polyricinoleate (PGPR, E476) is considered as the ‘classic’ surfactant when it comes to stabilization of W/O emulsions, the focal point of current research has recently shifted towards the use of particle stabilizers that allow longer term stabilization against coalescence and Ostwald ripening. In particular, Pickering stabilizers that are derived from natural, biodegradable sources, such as zein, cellulose, lignin, starch and polyphenol crystals (curcumin and quercetin), with or without further modification, have attracted burgeoning attention due to the rising popularity of ‘clean-label’ products amongst consumers. Using such particles, or intelligently combining particles with biopolymers to stabilize high water volume fractions in oil continuous matrices, plus the use of biopolymers to gel the water phase, offer promising new applications in food and allied soft matter manufacturing areas in the future.

Water-in-oil emulsions stabilized by surfactants, biopolymers and/or particles: a review

Water-in-oil (W/O) emulsions can be used to encapsulate and control the release of bioactive compounds for nutrition fortification in fat-based food products. However, long-term stabilization of W/O emulsions remains a challenging task in food science and thereby limits their potential application in the food industry. To develop high-quality emulsion-based food products, it is essential to better understand the factors that affect the emulsions' stability. In real food system, the stability situation of W/O emulsions is more complicated by the fact that various additives are contained in the products, such as NaCl, sugar, and other large molecular additives. The potential stability issues of W/O emulsions caused by these encapsulated additives are a current concern, and special attention should be given to the relevant theoretical knowledge. This article presents several commonly used methods for the preparation of W/O emulsions, and the roles of different additives (water- and oil-soluble types) in stabilizing W/O emulsions are mainly discussed and illustrated to gain new insights into the stability mechanism of emulsion systems. In addition, the review provides a comprehensive and state-of-art overview of the potential applications of W/O emulsions in food systems, for example, as fat replacers, controlled-release platforms of nutrients, and delivery carrier systems of water-soluble bioactive compounds. The information may be useful for optimizing the formulation of W/O emulsions for utilization in commercial functional food products.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/1541-4337.12482

Review on the Stability Mechanism and Application of Water-in-Oil Emulsions Encapsulating Various Additives

In recent years, substantial consideration within the food industry has been aimed at the development of food-grade nanoemulsions (NE) as promising systems for encapsulating, stabilizing, and delivering bioactive compounds. Although numerous studies have revealed the critical potential of NE, there are still several challenges to overcome them. These include the extensive amounts of synthetic emulsifiers needed for NE formulation, which can potentially be toxic for human health. The interest in safety, and natural emulsifiers have stimulated food manufacturers to develop "label-friendly" formulations by replacing synthetic emulsifiers with natural alternatives. This review represents a critical and comprehensive summary of the application of natural emulsifiers as potential substitutes for synthetic emulsifiers in NE production, with particular emphasis on the newly identified natural emulsifiers. Some recent reports showed the excellent emulsifying properties of various natural emulsifier extracted from natural resources, to produce NE, and therefore, might be generalized for further industrial applications. Future trends are encouraged to identify novel natural emulsifiers from industrial food by-products that may demonstrate highly effective emulsifiers.

Nanoemulsions: Using emulsifiers from natural sources replacing synthetic ones-A review.

Influence of flaxseed gum and NaCl concentrations on the stability of oil-in-water emulsions

In this study, lemon verbena essential oil as a natural antioxidant was used to increase the stability of sunflower oil, and stabilization effects in terms of storage conditions were compared with synthetic antioxidant (BHT). For this purpose, the antioxidant activity of the essential oil was determined by DPPH assay and β-carotene bleaching method. Then, lemon verbena essential oil (0, 400, 800, and 1,600 ppm) was added to sunflower oil without synthetic antioxidant and stored at 60°C for 60 days. Results from different parameters (peroxide value, free fatty acid, iodine value, total polar compound, carbonyl value, conjugated dienes, and oxidative stability index) were in agreement with each other, suggesting that lemon verbena essential oil (1,600 ppm) could act better than BHT in inhibition of lipid oxidation in sunflower oil and can be used as predominant alternative of synthetic antioxidants.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/fsn3.637

Evaluation of antioxidant properties of lemon verbena (Lippia citriodora) essential oil and its capacity in sunflower oil stabilization during storage time.

Influence of formulation on the oxidative stability of water-in-oil emulsions

Characterization of lipid oxidation in plant oils by micro-calorimetry.

Hexadecane-in-water emulsions were fabricated by means of a microfluidizer using two types of protein stabilizers, sodium caseinate (NaCAS) and β-lactoglobulin (BLG). A study of the dependence of the mean droplet diameter and protein coverage on protein concentration was performed. At low protein concentrations, the emulsions were monodispersed and their mean droplet size was governed by the so-called limited-coalescence process. In this regime, the interfacial coverage was constant and was deduced from the linear evolution of the total interfacial area as a function of the amount of adsorbed proteins. In emulsions based on NaCAS, almost all of the initial protein contents were adsorbed at the interfaces. Emulsions formulated at very low protein content underwent unlimited coalescence after prolonged storage or when submitted to centrifugation. Additional NaCAS was incorporated in the continuous phase, right after the emulsification process, as a means of ensuring kinetic stability. The interfacial covera...

/pdf/monodisperse-oil-in-water-emulsions-stabilized-by-proteins-355ydxyzzh.pdf

Monodisperse Oil-in-Water Emulsions Stabilized by Proteins: How To Master the Average Droplet Size and Stability, While Minimizing the Amount of Proteins

Direct technique for monitoring lipid oxidation in water-in-oil emulsions based on micro-calorimetry.

We describe the fabrication, the osmotic resistance, and the texture of highly concentrated oil-in-water emulsions stabilized by sunflower proteins. Fine and dilute emulsions (∼20 vol%)with narrow size distributions were concentrated by centrifugation and/or water evaporation without being destroyed. The concentrated emulsions resembled pastes whose rheological features were continuously tuned from weak to hard gels by increasing the droplet volume fraction from 65 to 99 vol%. The osmotic resistance normalized by Laplace pressure, γ/R, with γ being the oil/water interfacial tension and R the average droplet radius, was much higher than that of emulsions stabilized by conventional surfactants. This property was discussed considering the specific properties of interfacial films comprising unfolded globular proteins. The emulsions were also submitted to freeze-drying, and the obtained powders were redispersible in water. This approach opens up the possibility to use vegetable oils and proteins as substitutes of hydrogenated oils and/or of saturated fats for the formulation of texturized foods. 

/pdf/chapter-1-concentrated-o-w-emulsions-stabilized-by-proteins-2jjtew3n.pdf

Wafa Dridi

Papers

Influence of formulation on the oxidative stability of water-in-oil emulsions

Characterization of lipid oxidation in plant oils by micro-calorimetry.

Monodisperse Oil-in-Water Emulsions Stabilized by Proteins: How To Master the Average Droplet Size and Stability, While Minimizing the Amount of Proteins

Direct technique for monitoring lipid oxidation in water-in-oil emulsions based on micro-calorimetry.

Chapter 1. Concentrated O/W Emulsions Stabilized by Proteins: A Route to Texturize Vegetal Oils Without Using Trans or Saturated Fats