Abstract:

The aim of this study was to compare the effects of ultrasonic treatments at three different power levels (150,
300 and 450 W) for different durations (12 and 24 min) on the structural and functional properties of soybean protein
isolate (SPI)-phospholipid composite system. Scanning electron microscope observation and rheology experiments showed
that ultrasonic treatments at low and medium powers were suitable to generate compact and uniform gel with high elastic
modulus. When the ultrasonic condition remained at 300 W for 24 min, the sample showed the best gel properties. It was
confirmed that gel properties were influenced by the conformation of soybean protein-phospholipid composite system.
Raman spectra showed that ultrasonic treatment could change the secondary structure of SPI. The microenvironment of tryptophan
and tyrosine residues was changed at the same time. The interactions between SPI and lecithin easily occurred because of the
exposure of hydrophobic groups. Low and medium power ultrasonication had a stronger effect on the composite system. Insoluble
protein aggregates occurred when ultrasonic power increased to 450 W, and the functional properties of the composite system
decreased because the interactions between soybean protein isolate and lecithin became weaker.

Key words: ultrasonic treatment, soybean protein isolate-phospholipid composite system, fluorescence spectroscopy, Raman spectroscopy, spatial structure