Ultrasound-assisted fabrication and stability evaluation of okra seed protein stabilized nanoemulsion

The structure and functional properties of okra seed protein (OSP) were characterized, the ultrasonic homogenization process of OSP nano-emulsion was optimized by response surface methodology (RSM), and its stability was also evaluated in this study. The results suggested that OSP was a high-quality plant protein, rich in glutamic acid. The molecular weight of its main subunits distributed in the range of 10-55 kDa, and some subunits were connected by disulfide bonds. Although the water and oil holding capacities of OSP were inferior to those of soy protein isolate (SPI), its emulsifying ability was superior to that of SPI. And the OSP concentration, ultrasonic time and ultrasonic power had obvious effects on the droplet size of nanoemulsion. The optimum process of OSP emulsion was determined as follows: OSP concentration 2.4 %, ultrasonic power 600 W, ultrasonic time 340 s. Under these conditions, the median droplet size of the nanoemulsion was 192.03 ± 3.48 nm, close to the predicted value (191.195 nm). And the obtained nano-emulsion exhibited high stability to the changes of pH, temperature and ionic strength in the environment. Our results can provide reference for the application of OSP, and promote the development of plant protein-based nanoemulsions.

Interaction mechanism of okra (Abelmoschus esculentus L.) seed protein and flavonoids: Fluorescent and 3D-QSAR studies

The binding capacity of 10 flavonoids with okra seed protein (OSP) was studied by fluorescence spectroscopy. The structure of flavonoids had an obvious impact on binding performance. The binding ability of flavanone was lower than that of flavone, isoflavone and dihydrochalcone. The binding capacity of flavonoid glycoside was superior to that of the corresponding flavonoid aglycone. The binding ability was positively correlated with the number of phenolic hydroxyl groups on the B ring. The steric field and electrostatic field model constructed by 3D-QSAR method could well explain the above interaction behavior. Thermodynamic analysis suggested that the quenching mechanism of OSP caused by flavonoids was static quenching, and the binding-site number was 1. In addition, hydrogen bonding and van der Waals force dominated this interaction. The 3D and synchronous fluorescence spectra showed that there was no significant change in the polarity of the environment around tryptophan and tyrosine residues during binding.