Singlet oxygen quenching activity of furan fatty acids: Kinetic and thermodynamics study

We have undertaken a detailed study of the reactivity of furan fatty acids (F-acids) with singlet oxygen (¹O₂) produced by thermal decomposition of endoperoxide and photosensitizer reaction of rose bengal in ethanol. Accordingly, we measured the second order rate constant (k_Q) for the reaction of F-acids with ¹O₂. As a result, the reactivity of F-acids against ¹O₂ exhibited a decrease in the order tetra-alkyl F-acid (F₃) > tri-alkyl F-acid (F₂) > di-alkyl F-acid (NMF). In addition, we also employed the density functional theory (DFT) and quantum chemical calculations to predict the chemical reactivity, stability, and thermodynamic properties of F-acids with respect to the quenching ¹O₂. In consequence, it is clear that log k_Q values of F-acids correlate with the energy level of the highest occupied molecular orbital (E_HOMO), and HOMO of F-acids may react with the lowest unoccupied molecular orbitals (LUMO) of ¹O₂. Moreover, the reaction of F-acids with ¹O₂ proceeds spontaneously in ethanol based on the calculation by thermodynamics method. These results suggest that the F-acids may contribute to the protection of oxidative damage in animals by quenching ¹O₂.     

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

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.