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The nanoemulsions of soy protein isolate-phosphatidylcholine (SPI-PC) with different emulsion conditions were studied. Homogenization pressure and homogenization cycle times were varied, along with SPI and PC concentration. Evaluations included turbidity, particle size, ζ-potential, particle distribution index, and turbiscan stability index (TSI). The nanoemulsions had the best stability when SPI was at 1.5%, PC was at 0.22%, the homogenization pressure was 100 MPa and homogenization was performed 4 times. The average particle size of the SPI-PC nanoemulsions was 217 nm, the TSI was 3.02 and the emulsification yield was 93.4% of nanoemulsions.

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Ultrasound treatment and high-pressure homogenization were used to prepare soybean protein (SP)-phosphatidylcholine (PC) nanoemulsions in this study. Nanoemulsions prepared by high-pressure homogenization were more stable. The structural changes of SP and PC under ultrasound treatment and high-pressure homogenization treatment were investigated by Raman spectroscopy. It could be concluded that ultrasound and high-pressure homogenization treatments increased both the content of α-helix and unordered structure but decreased that of β-structures of SP, while the interaction between SP and PC decreased α-helix content and also reduced unordered structure and β-sheet structure. Ultrasound treatment and high-pressure homogenization exposed more tryptophan and tyrosine residues to promote hydrophobic interaction between SP and PC, which was beneficial for stabilizing the nanoemulsion. The SP-PC interaction exerted a more significant effect on side chain structure than those observed under ultrasound treatment and high-pressure homogenization. The dominant g-g-t vibrational mode of the disulfide bond of soybean protein was not appreciably changed by the two preparations. High-pressure homogenization increased the disorder of lipid chains of PC, promoting SP-PC interaction and thereby increasing the stability of the nanoemulsion. The structural change provided a theoretical basis for preparation of two nanoemulsions.

The variations in average particle size, zeta potential, free fatty acids (FFA) release rate, and the bioavailability of menthol under in vitro simulated digestion conditions of peppermint oil nanoemulsion were investigated. 3D confocal laser scanning microscopy and Cryo-scanning electron microscopy were used to observe the microstructure characteristics of peppermint oil nanoemulsion, which indicated that soybean protein was completely adsorbed at the oil-water interface of the nanoemulsion and presented a core shell structure. And the results indicated that FFA release rate and menthol bioavailability of peppermint oil nanoemulsion prepared by using high-pressure homogenization were much higher. In the simulated gastric digestion phase, the average particle size and the zeta potential of the nanoemulsion increased, and droplet polymerization appeared. After the simulated intestinal, the interfacial protein of nanoemulsion was hydrolyzed, and the oil droplets were digested, which resulted in the decreased particle size and increased absolute value of zeta potential.