Effect Of High Intensity Ultrasonic Treatment On Structure And Emulsification Of Soy Protein Isolate

Soy protein isolate(SPI)has many excellent processing properties and is widely used in the food industry.According to research reports in recent years,the application of high intensity ultrasound technology can significantly improve the structure of soybean protein isolate,which in turn affects its functional properties.However,there are few studies on the structure changes of soybean protein isolates produced by different extraction processes,different concentrations of ultrasonic power under different powers,and their emulsification.(1)The experimental results in this paper show that the SPI extracted by the alkali-soluble acid precipitation method after ultrasonic treatment has significantly improved the solubility of all samples.The 5% SPI can produce higher solubility,but the ultrasonic treatment increases the solubility of the 3% SPI relatively more.After all samples were sonicated,the turbidity decreased significantly.The destruction of SPI extracted by the alkali-soluble acid precipitation method caused by ultrasonic treatment reduced the aggregates and the particle size.800 W ultrasound at 5% SPI makes the aggregates increase and the particle size increases.Circular dichroism,free sulfhydryl,electrophoresis,and scanning electron microscopy showed that ultrasound did not significantly affect the SPI structures.(2)The 200 W–800 W high intensity ultrasonic treatment used in this paper significantly improved the solubility of commercial SPI.When the ultrasonic treatment was performed at lower power(200 W and 400 W),the protein molecular aggregates were broken up and the average particle size became smaller.At the same time,the hydrophobic interaction weakens and the solubility increases.Higher power(600 W and 800 W)causes partial re-polymerization of protein molecules,enhanced hydrophobic interaction,particle size becomes larger,and solubility decreases.At 200 W and 400 W,3% SPI has higher solubility,and also has a higher solubility increase increment.After 600 W ultrasound,the solubility of the two concentrations of SPI is close to each other.After 800 W ultrasound,5% SPI has a higher solubility.Gel electrophoresis results showed that ultrasonic treatment did not damage the commercial SPI subunits at two concentrations.Scanning electron microscopy results showed that all lyophilized samples showed a similar sheet structure.(3)After adding commercial SPI as an emulsifier,the average particle size of the emulsion decreased overall.Droplets with a large particle size distribution decreased significantly,and droplets with a small particle size distribution increased significantly.The reason for the bimodal distribution of particle size distribution is that the particle size of SPI without ultrasonic treatment is uneven,and protein aggregates and protein molecules coexist in the system.At this time,the emulsion system formed by SPI has obvious aggregation and flocculation behavior.Low-power ultrasound(200 W and 400 W)significantly reduced the particle size of commercial SPI.After 600 W and 800 W ultrasonic treatment,the particle size of SPI increased significantly.The pictures given by AFM and CLSM confirm the results of the third chapter of this study,such as particle size and solubility.It also provides the theoretical basis of morphology for the further study of the effect of ultrasound on the emulsification of commercial SPI.