Abstract
This study investigated the preparation and properties of corn oil nanoemulsions stabilized by peanut protein isolate (PPI), rice bran protein isolate (RBPI), soybean protein isolate (SPI), and whey protein isolate (WPI). The mean droplet diameter of four protein-stabilized nanoemulsions prepared via ultrasound method was less than 245 nm. PPI-stabilized nanoemulsions showed better stability for 4 weeks, while the mean droplet diameter of RBPI-stabilized nanoemulsions had exceeded 1000 nm during the third week of storage. Fourier transform infrared and interfacial tension (IT) analysis showed that the higher level of disordered structure and lower IT of proteins made the stability of nanoemulsions better. Moreover, bivariate correlation analysis discovered that α-helix (p < 0.01) and β-turn (p < 0.05) of proteins were related to the mean droplet diameter of nanoemulsions, the random coil (p < 0.05) was related to the zeta potential of nanoemulsions. This study provided new idea for the relationship between the structure of protein and properties of protein-stabilized nanoemulsions.
Highlights
Nanoemulsions are composed by minute oil droplets which are maintained in the aqueous phase
It should be noticed that there was followed by another increase trend of mean droplet diameter (MDD) when the concentration of protein further increased to a certain degree. This phenomenon was attributed to the fact that the numbers of interfacial sites were insufficient for the large number of protein molecules and unabsorbed protein molecules led to the aggregation in aqueous phase [30]
The results indicated that peanut protein isolate (PPI) and rice bran protein isolate (RBPI) were more efficient at debasing particle size of nanoemulsions when they were at lower protein concentrations (2% w/v)
Summary
Nanoemulsions are composed by minute oil droplets (average droplet diameter less than 500 nm) which are maintained in the aqueous phase. Each nanoemulsion oil droplet is usually stabilized by emulsifier molecules. Nanoemulsions have acted as an excellent system for the encapsulation and delivery of bioactive compounds which are lipophilic in nature. The nanoemulsions characteristics, such as the droplet size distribution, optical and rheological stability, are governed by emulsification technologies and emulsifier types [5]. High and low energy emulsification approaches are usually employed for nanoemulsions preparation. Spontaneous emulsification (microemulsion dilution and solvent diffusion) and phase transition (by adjusting component or temperature) are two commonly used low energy emulsification approaches [6]. Compared with low energy emulsification methods, high energy approaches are more frequently utilized to produce nanoemulsions, especially in large scale production of food industry. The ultrasonic cavitation can increase diffusion rates and Nanomaterials 2019, 9, 25; doi:10.3390/nano9010025 www.mdpi.com/journal/nanomaterials
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