Nanoemulsions fabricated from food-grade ingredients are being increasingly utilized in the food industry to encapsulate, protect, and deliver lipophilic functional components, such as biologically-active lipids (e.g., ω-3 fatty acids, conjugated linoleic acid) and oil-soluble flavors, vitamins, preservatives, and nutraceuticals. The small size of the particles in nanoemulsions (r<100 nm) means that they have a number of potential advantages over conventional emulsions-higher stability to droplet aggregation and gravitational separation, high optical clarity, ability to modulate product texture, and, increased bioavailability of lipophilic components. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This review article provides an overview of the current status of nanoemulsion formulation, fabrication, properties, applications, biological fate, and potential toxicity with emphasis on systems suitable for utilization within the food and beverage industry.

Food-grade nanoemulsions: formulation, fabrication, properties, performance, biological fate, and potential toxicity.

There is increasing interest within the food, beverage and pharmaceutical industries in utilizing edible nanoemulsions to encapsulate, protect and deliver lipophilic functional components, such as oil-soluble flavors, vitamins, preservatives, nutraceuticals, and drugs. There are a number of potential advantages of using nanoemulsions rather than conventional emulsions for this purpose: they can greatly increase the bioavailability of lipophilic substances; they scatter light weakly and so can be incorporated into optically transparent products; they can be used to modulate the product texture; and they have a high stability to particle aggregation and gravitational separation. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This tutorial review provides an overview of the current status of nanoemulsion fabrication, properties, and applications with special emphasis on systems suitable for utilization within the food industry.

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Edible nanoemulsions: fabrication, properties, and functional performance

As the continues to improve the nutritional content of their products, challenges in prevention of rancidity have increased due to the presence of more polyunsaturated fatty acids. In addition, consumer demand for all natural foods has limited the use of traditional methods to control lipid oxidation such as synthetic antioxidants and hydrogenation. To overcome these challenges a better understand the mechanisms of lipid oxidation are needed so that novel antioxidant technologies can be developed. Lipids in foods often exist as dispersions stabilized by emulsifiers that provide physical stability. Food emulsions contain an oil-water interface that has major impact on the lipid oxidation pathways by influencing the location and reactivity of prooxidative transition metals, lipid hydroperoxides, minor lipid components, free radical scavengers and metal chelators. Understanding how the physical properties of the lipid–water or lipid–air interface in food dispersions impacts oxidation chemistry has lead to new strategies to create lipid structures that slow down the development of rancidity by decreasing interaction between lipids in the emulsion droplet core with prooxidants and oxygen as well as increasing antioxidant concentrations at the site of oxidation.

Mechanisms of lipid oxidation in food dispersions

More polyunsaturated fats in processed foods and fewer additives are a huge demand of public health agencies and consumers. Consequently, although foods have an enhanced tendency to oxidize, the usage of antioxidants, especially synthetic antioxidants, is restrained. An alternate solution is to better control the localization of reactants inside the food matrix to limit oxidation. This review establishes the state-of-the-art on lipid oxidation in oil-in-water (O/W) emulsions, with an emphasis on the role of the interfacial region, a critical area in the system in that respect. We first provide a summary on the essential basic knowledge regarding (i) the structure of O/W emulsions and interfaces and (ii) the general mechanisms of lipid oxidation. Then, we discuss the factors involved in the development of lipid oxidation in O/W emulsions with a special focus on the role played by the interfacial region. The multiple effects that can be attributed to emulsifiers according to their chemical structure and their location, and the interrelationships between the parameters that define the physicochemistry and structure of emulsions are highlighted. This work sheds new light on the interpretation of reported results that are sometimes ambiguous or contradictory.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12097

Lipid Oxidation in Oil‐in‐Water Emulsions: Involvement of the Interfacial Layer

Antioxidant Role for Lipid Droplets in a Stem Cell Niche of Drosophila

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806±0.0690, 3.28±0.0660, or 10.7±0.106 μm (mean ± SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 μm were significantly lower than those in the emulsion with a mean droplet size of 12.8 μm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 μm were lower compared with those of the emulsion with a mean droplet size of 12.8 μm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by 1H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.

Effects of droplet size on the oxidative stability of oil-in-water emulsions

By conducing organoleptic analysis, the authors investigated the effect of oil droplet size on human preference to the taste of oil-in-water (o/w) emulsions to which several tastants were added. Two singly dispersed o/w emulsions, different in oil droplet sizes, consisting of 10% triacilglycerol purified from tuna, sardine or soybean oil, 0.5% emulsifier and water were prepared by ceramic membrane filtration. Organoleptic analysis showed that the impressions of sweetness, bitterness and umami, which were developed by addition of certain taste substances, were different between o/w emulsions with different oil droplet sizes. The results of two-bottle choice tests, which were carried out using olfactory-blocked mice, showed that o/w emulsions with 1.00-μm droplets, with added sweet or bitter substances, were preferred to emulsion with 5.50-μm droplets. These results suggest that the droplet size of o/w emulsion remarkably influences certain taste impressions created by added taste substances.

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Kyoko Nakaya

Papers

Effects of droplet size on the oxidative stability of oil-in-water emulsions

Effect of oil droplet sizes of oil-in-water emulsion on the taste impressions of added tastants