Will lipid oxidation influence the physiochemical stability and bioaccessibility of rare ginsenoside PPD nanoemulsions?

Rare ginsenosides have many pharmacological functions; however, their bioaccessibility is quite limited owing to the poor solubility. Emulsion-based delivery systems provide a good solution to this; however, the effects of lipid oxidation in emulsions have not been well studied. In this study, ginsenoside PPD nanoemulsions were prepared by using soybean oil oxidized by heating at 60 °C for 3, 5, and 7 days (defined as low, medium, and high oxidation degree oxidation) and investigated the effect of lipid oxidation on the physicochemical and gastrointestinal digestion characteristics of ginsenoside nanoemulsions. The results showed that lipid oxidation had no significant effect on particle size, ζ-potential, centrifugal stability and turbidity of ginsenoside nanoemulsions. The pH value and freeze-thaw stability of emulsions decreased as the oxidation degree increased; moreover, lipid oxidation significantly decreased encapsulation rate and bioaccessibility of ginsenoside PPD in the nanoemulsions. In details, the encapsulation rate of ginsenoside PPD decreased from 90.05 ± 0.40% to 84.41 ± 0.99% as the lipid oxidation increased. Low lipid oxidation degree has no obvious effects on the fatty acid release rate and bioaccessibility of ginsenoside during digestion process, while higher lipid oxidation decreased the release of fatty acids and ginsenoside bioaccessibility from 64.15 ± 0.59% to 55.40 ± 0.97%. The results of this study shed lights on improving the bioavailability of rare ginsenosides, and provided a guidance for the selection of lipid criteria in emulsion delivery systems.