Abstract: In order to improve the functional properties of oleosin, the effects of alkali and ultrasonic treatments alone and in combination on the structure, solubility and emulsifying properties of oleosin were studied. The mechanism of structural changes of protein aggregates under different treatment conditions was also discussed. The microstructure, hydrodynamic radius, internal structure and spatial structure of modified oleosin were studied by atomic force microscopy, dynamic laser scattering, fluorescence spectroscopy and circular dichroism microscopy. The results showed that ultrasonic treatment could promote the transformation of oleosin from insoluble aggregates to soluble ones, and the solubility of oleosin subjected to ultrasonic treatment alone or in combined with alkali treatment increased by 124% and 162% compared to the control, respectively (P < 0.05). Circular dichroism and fluorescence spectroscopy showed that both ultrasonic and alkali treatments could promote the unfolding of protein structure, thus promoting the exposure of more hydrophobic groups such as tyrosine and tryptophan. Compared with the control group, the α-helix content of oleosin increased by 17.7% and the β-folding content decreased by 9.2% after the combined treatment. At the same time, the particle size decreased (286.0 nm) and the emulsifying properties improved (emulsion stability index of 575.0 g/m2, and emulsifying activity index of 605.4 min). This study provides a reference for improved functions of oleosin.

Key words: oleosin, functional properties, ultrasonic, protein structure