Lipid oxidation metal-emulsions droplet

An important question to consider is where does metal catalysis takes place in multiphase systems In bulk oils systems, the hydrophilic metals would be oriented in the air-oil interface to catalyse lipid oxidation (Figure 10.7). In emulsions and liposomes, the metals would be in solution in the aqueous phases and oriented in either the oil-water or phospholipid-water interfaces, where they may have an affinity for the hydrated layer around the droplets (Figure 10.4). 

The interfacial thickness of emulsion droplets is an important parameter affecting lipid oxidation reaction rates. Increasing interfacial membrane thickness can conceivably hinder the physical interaction between aqueous phase prooxidants (e.g., transition metals) and emulsified lipids(Chaiyasit et al., 2000 Silvestre et al., 2000). For example, Silvestre and co-workers (2000) showed that iron-catalyzed cumenehydroperoxide reduction, as well as salmon oil-in-water emulsion oxidation, was slower when Brij 700 was used in place of Brij 76. Brij 700 and 76 are small molecule surfactants with identical hydrophobic tail group lengths (CHjlCH lj -), but vary only with respect to the size of their polar head groups Brij 700 and Brij 76 consist of 100 and 10 oxyethylene head groups, respectively. Lower hydroperoxide decomposition and lipid oxidation rates in Brij 700-stabilized emulsions suggest that a thicker interfacial layer was able to act as a physical barrier to decrease lipid-prooxidant interactions (Silvestre et al., 2000). 

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