Comparison of antioxidant efficiencies in oil-in-water emulsion using extracellular vesicles from olive co-products or liposomes as antioxidants carriers

Olive extracellular vesicles and synthetic liposomes were evaluated as carriers of antioxidants to stabilize oil-in-water emulsions against oxidative degradation. For this, hydroxytyrosol, rosmarinic acid and their lipophilic counterparts, (hydroxytyrosyl dodecanoate esters or eicosyl rosmarinate esters) were loaded into these carrier vesicles and the antioxidant efficiencies of these formulations were compared with those of the corresponding antioxidants alone. Using the conjugated autoxidizable triene assay (CAT assay), our results shows that loaded synthetic liposome mimicking the lipid membrane composition of olive extracellular vesicle allowed to enhance the antioxidant effect of the loaded antioxidant especially with the two lipophilic hydroxytyrosol and rosmarinic acid esters. On the contrary, the loading of the studied antioxidant into the olive extracellular vesicles did not result in an improvement of the antioxidant activity. The antioxidant effects of loaded vesicles were also evaluated in rapeseed oil (1% w/w)-in-water emulsions that were stored at 40°C for 21 days and for which oxidative status was monitored by the quantification of primary and secondary oxidation compounds. In that case, the boosting effect of liposomal carriers was not confirmed. This could be due to a different type of emulsions compared to the one used with the CAT assay as different surfactants and oxidation inducers were employed. Additionally, the limited physical stability of the carrier could be involved as liposomes loaded with the most lipophilic antioxidants, namely hydroxytyrosyl dodecanoate and eicosyl rosmarinate were shown to be instable for period exceeding 10 days of storage.