Polyphenolic Antioxidants in Lipid Emulsions: Partitioning Effects and Interfacial Phenomena

Abstract

The autoxidation of lipids in complex systems such as emulsions or biological membranes, although known to occur readily and to be associated with important pathological events, is lacking in quantitative data in spite of the huge efforts that have been made in attempting to unravel the complex mechanisms of lipid oxidation and its inhibition by antioxidants. Lipids are present as oil-in-water emulsions in many foods and pharmaceutical formulations, and the prevalent role of the interfacial region is critical to understand the antioxidant behavior and to correctly interpret antioxidant efficiencies. The aim of this review is to summarize the current knowledge on the chemical fate of antioxidants before they react with peroxyl radicals. Many researchers highlighted the predominant role of interfaces, and although some attempts have been made to understand their role, in most instances, they were essentially qualitative and based on putative hypotheses. It is only recently that quantitative reports have been published. Indeed, knowledge on the effects of relevant experimental variables on the effective concentrations of antioxidants is necessary for a successful design of alternate, effective antioxidative solutions.

Modeling Chemical Reactivity at the Interfaces of Emulsions: Effects of Partitioning and Temperature

“…Our research on antioxidants in fluid emulsions over the past decade demonstrates that the dynamic equilibrium condition holds provided that the emulsions are either kinetically stable or gently stirred after initial mixing because the intermolecular interactions between molecules and ions in emulsions are generally weak and their diffusivities should be orders of magnitude faster than the rates of thermal reaction [ 3 , 4 , 19 , 24 , 25 , 34 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ].…”

“…Conversely, very hydrophobic antioxidants (high values) are water insoluble and only partition between the oil and interfacial regions. Cautions must be taken, however, because values for food-grade oils cannot be extrapolated from the values in octanol–water binary systems (probably the most common system employed to determine the hydrophobicity of a molecule) because the solvents are totally different [ 3 , 19 , 24 , 90 ].…”

“…The effective H + concentration in the interfacial region (mole per liter of interfacial volume) should be reduced to approximately the same amount as the TBHQ and TBHQ − concentrations. Therefore, the decrease in k obs with increasing Φ I is caused by dilution of the TBHQ anion within the increasing volume of the totality of the interfacial regions of the emulsions droplets as in nonionic emulsions, Figure 7 A [ 3 , 19 , 85 ].…”

“…The three-dimensional interfaces between two immiscible liquids (oil and water) found in emulsions and other colloidal systems have been widely used as models of membrane function to mimic their behavior, as models of lipid-based foods and to model important (bio)chemical reactions such as the oxidation of lipids [ 1 , 2 , 3 , 4 ]. A variety of fundamental processes involved in biocatalysis, such as ion pumping, electron transport, membrane fusion, and photosynthesis, have all been investigated in such interfacial systems for further guidance in developing new biomaterials and medicines and to better understand life science [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ].…”

Effects of Surfactant Volume Fraction on the Antioxidant Efficiency and on The Interfacial Concentrations of Octyl and Tetradecyl p-Coumarates in Corn Oil-in-Water Emulsions

“…Control of the lipid oxidation reaction is, therefore, a challenge not only for the food industry but also for the pharmaceutical industry, where unsaturated lipids are employed in the formulation of products of interest, such as the nutritive emulsions employed in parenteral nutrition, and for the cosmetics industry, where they are widely used in the preparation of lotions, beauty creams, etc. One of the most effective ways of inhibiting the oxidation of lipid-based foods is the incorporation of antioxidants, AOs, which are molecules capable of donating H-atoms to lipid radicals to regenerate them [ 4 , 12 , 13 ]. The efficiency of the AOs in inhibiting lipid oxidation is usually assessed in terms of the rate of the chemical reaction between the AO and the lipid radical, which depends on, among others, the effective concentrations of the antioxidant in the interfacial region of the emulsions [ 13 , 14 , 15 , 16 , 17 , 18 ].…”