Assembled structure and interfacial properties of oleosome-associated proteins from Camellia oleifera as natural surface-active agents

A very low content of oleosome-associated proteins (OAPs) allows for long-term stability of oleosomes in mature seeds, but there is limited knowledge on these interfacial behaviors. Here, the effect of extraction solvents on the composition, structure, and interfacial properties of OAPs from Camellia oleifera were investigated. After lipid removal by cold acetone/ether (AE) and chloroform/methanol (CM), the OAPs-AE exhibited a white lumpy morphology, but the OAPs-CM was a transparent film. The major components of OAPs-AE and OAPs-CM were similar, including oleosin, Ole Ⅰ, Ole Ⅱ, Ole Ⅳ, and Ole Ⅴ. The OAPs-CM had more α-helix (∼60%) and β-sheet (∼15%) structures than that of OAPs-AE, while the OAPs-AE had a higher denaturation temperature (∼90.9 °C). The residual phospholipid content in OAPs-AE was 21.5 times that of OAPs-CM. The OAPs-AE displayed an impressive ability to increase surface pressure at the air–water interface (∼32 mN/m at 4000 s) and oil–water interface (∼12 mN/m at 4000 s), even at a very low concentration (0.04 mg/mL). For the air–water interface, the diffusion rate of OAPs-AE was faster than that of OAPs-CM at all of the investigated pH values. These results provide a better understanding of OAPs as novel natural surface-active agents.