Effect of ubiquinol-10 on citral stability and off-flavor formation in oil-in-water (O/W) nanoemulsions

The effects of different concentrations of ubiquinol-10 (Q ₁₀H₂) on citral's stability were systematically investigated and compared in citral-loaded oil-in-water (O/W) nanoemulsions. Solid phase microextraction gas chromatography (SPME-GC) was employed to monitor the degradation of citral and the formation of off-flavor compounds throughout storage at 25 and 45 C. The optimum concentration of Q₁₀H₂ in the current formulation was determined to be around 0.10 wt % in the system (Q₁₀H₂/citral ratio 1:1), which can effectively protect citral from chemical degradation and oxidation. Results suggested, however, that a low concentration of Q₁₀H₂ may induce the majority of the ubisemiquinone (Q₁₀^•-)/ubiquinone (Q ₁₀) redox transition, which possibly endowed Q₁₀H ₂ with pro-oxidant properties. Further increase in Q ₁₀H₂ concentration beyond a certain value also hindered its effect due to the complex properties of radicals involved and the overall environment encountered. With appropriate concentrations of Q₁₀H ₂ presented in the system, major citral oxidation off-flavor compounds (p-cresol, α,p-dimethylstyrene, p-methylacetophenone), and some of the lipid degradation products can be inhibited to lower levels. In contrast, ubiquinone-10 (Q₁₀) had a negligible effect on citral's chemical stability and off-flavor generation.