The susceptibility of lipids to oxidation is a major cause of quality deterioration in food emulsions. The reaction mechanism and factors that influence oxidation are appreciably different for emulsified lipids than for bulk lipids. This article reviews the current understanding of the lipid oxidation mechanism in oil-in-water emulsions. It also discusses the major factors that influence the rate of lipid oxidation in emulsions, such as antioxidants, chelating agents, ingredient purity, ingredient partitioning, interfacial characteristics, droplet characteristics, and ingredient interactions. This knowledge is then used to define effective strategies for controlling lipid oxidation in food emulsions.

The official International Dairy Federation method for determination of the peroxide value of anhydrous milk fat was extended to poultry, meat, fish, and vegetable oils. The ferrous oxidation–xylenol orange method for determination of peroxide values of liposomes and lipoproteins was modified to make it simpler and more rapid. These 2 spectro-photometric methods were used successfully to determine the peroxide values of beef, chicken, butter, fish, and vegetable products. The results in most cases were consistent with those obtained by using the AOAC Official Method. The spectro-photometric methods have an assay time of less than 10 min, require ≤0.3 g fat, and are capable of determining peroxide values as low as 0.1 mequiv/kg of sample.

Proteins can inhibit lipid oxidation by biologically designed mechanisms (e.g. antioxidant enzymes and iron-binding proteins) or by nonspecific mechanisms. Both of these types of antioxidative proteins contribute to the endogenous antioxidant capacity of foods. Proteins also have excellent potential as antioxidant additives in foods because they can inhibit lipid oxidation through multiple pathways including inactivation of reactive oxygen species, scavenging free radicals, chelation of prooxidative transition metals, reduction of hydroperoxides, and alteration of the physical properties of food systems. A protein's overall antioxidant activity can be increased by disruption of its tertiary structure to increase the solvent accessibility of amino acid residues that can scavenge free radicals and chelate prooxidative metals. The production of peptides through hydrolytic reactions seems to be the most promising technique to form proteinaceous antioxidants since peptides have substantially higher antioxidant activity than intact proteins. While proteins and peptides have excellent potential as food antioxidants, issues such as allergenicity and bitter off-flavors as well as their ability to alter food texture and color need to be addressed.

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There is a pressing need for edible delivery systems to encapsulate, protect, and release bioactive lipids within the food, medical, and pharmaceutical industries. The fact that these delivery systems must be edible puts constraints on the type of ingredients and processing operations that can be used to create them. Emulsion technology is particularly suited for the design and fabrication of delivery systems for encapsulating bioactive lipids. This review provides a brief overview of the major bioactive lipids that need to be delivered within the food industry (for example, ω-3 fatty acids, carotenoids, and phytosterols), highlighting the main challenges to their current incorporation into foods. We then provide an overview of a number of emulsion-based technologies that could be used as edible delivery systems by the food and other industries, including conventional emulsions, multiple emulsions, multilayer emulsions, solid lipid particles, and filled hydrogel particles. Each of these delivery systems could be produced from food-grade (GRAS) ingredients (for example, lipids, proteins, polysaccharides, surfactants, and minerals) using simple processing operations (for example, mixing, homogenizing, and thermal processing). For each type of delivery system, we describe its structure, preparation, advantages, limitations, and potential applications. This knowledge can be used to facilitate the selection of the most appropriate emulsion-based delivery system for specific applications.

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In recent years, a number of studies have produced evidence to suggest that consuming carotenoids may provide a variety of health benefits including a reduced incidence of a number of cancers, reduced risk of cardiovascular disease, and improved eye health. Evolving evidence on the health benefits of several carotenoids has sparked interest in incorporating more carotenoids into functional food products. Unfortunately, the same structural attributes of carotenoids that are thought to impart health benefits also make these compounds highly susceptible to oxidation. Given the susceptibility of carotenoids to degradation, particularly once they have been extracted from biological tissues, it is important to understand the major mechanisms of oxidation in order to design delivery systems that protect these compounds when they are used as functional food ingredients. This article reviews current understanding of the oxidation mechanisms by which carotenoids are degraded, including pathways induced by heat, light, oxygen, acid, transition metal, or interactions with radical species. In addition, several carotenoid delivery systems are evaluated for their potential to decrease carotenoid degradation in functional food products.

Lipid oxidation is important to food manufacturers especially when they increase unsaturated lipids in their products to improve nutritional profiles. Unfortunately, the number of antioxidants available to food manufacturers to control oxidative rancidity is limited and the approval of new antioxidants is unlikely due to economic barriers in obtaining government approval for new food additives. Therefore, new antioxidant technologies are needed for food oils. This paper reviews the current knowledge of lipid oxidation in foods with emphasis on how physical properties of food systems impact oxidation chemistry. In particular, the role of association colloids in bulk oils on lipid oxidation chemistry is discussed in an attempt to understand mechanisms of oxidation. Increasing the understanding of how physical properties impact lipid oxidation could lead to the development of novel antioxidant technologies that not only protect the oil against oxidation and increase shelf-life but also allow food manufacturers to include more nutritionally beneficial fatty acids in their products.