Impact of interfacial barriers onthe oxidative stability of lipophilicbioactive compounds in oil-in-wateremulsions - The case of lutein

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An In-Depth Guide to Oil-in-Water Emulsions


Oils, which consist of fatty acids (FA), are dispersed in the aqueous phase of food emulsions. Under food processing conditions (e.g., high heat, shear forces), and in the presence of oxygen, polyunsaturated fatty acids (PUFA) may become oxidized. It is generally accepted that the interfacial region, which is the contact region between the oil phase and the aqueous phase, represents a critical area in the emulsion system with regard to the development of oxidation. A better understanding of the relationship between the interfacial region (oil droplet size) and interfacial composition (emulsifier type) may allow the creation of stable food emulsions against oxidation. Emulsifiers work by stabilizing oils suspended in water, and this is achieved electrostatically. A part of an emulsifier is attracted to water while its other part is attracted to the oil. The effects of emulsifiers in limiting the transport of free radicals across the emulsion interface and its impact on the oxidative stability of lipophilic bioactive compounds is an area of active research. The transport of free radicals across the emulsion interface can be measured using a peroxide method. The free radicals are generated in the aqueous phase using 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH). The peroxide method can reveal the barrier properties of emulsifiers towards a water-soluble radical initiator (AAPH) in emulsion systems. Lutein, a xanthophyll carotenoid, was selected as a lipophilic bioactive compound (phytonutrient) model to evaluate the interfacial barrier properties of emulsifiers in an emulsion-based delivery system prepared with corn oil, which is high in PUFA. The lutein-loaded emulsions were formulated with the following emulsifiers: bovine casein; caprine casein (αs1-I); and caprine casein (as1-II). The peroxide value (PV) demonstrated that lutein-loaded emulsions stabilized with caprine casein (αs1-II) provided a significantly (p < 0.05) enhanced interfacial barrier limiting the transport of peroxyl radicals across the oil-water interface. In agreement with PV measurements, chemical (color) stability results showed that lutein was most stable (p<0.05) under the photo-oxidative conditions when emulsions were stabilized by caprine casein (αs1-II). The better interfacial barrier properties exhibited by caprine casein (αs1-II) can be used to create lutein-loaded emulsion formulations with improved chemical (color) stability for food and beverage applications. Â

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