Abstract:

Ultrasonic treatments with different power (150, 300 and 450 W) for different durations (12 and 24 min) were
applied on soybean protein isolate-phospholipid system to evaluate their effects on the composite system. Functional
properties of the composite system as a function of ultrasonic conditions were explored at the same time. Circular dichroism
spectrum, particle size distribution, Zeta-potential, solubility and emulsibility were determined. The results showed that
ultrasonic treatment for 12 min with medium power (300 W) had the greatest impact on the composite system. The content
of α-helix decreased obviously, and the solubility and emulsibility were higher than those of the untreated sample. When
the ultrasonic treatment time increased to 24 min, low ultrasonic power could significantly increase emulsifying properties
of the system. Particle size decreased from 16.87 μm to 6.49 μm and the absolute value of Zeta-potential increased. The
content of α-helix decreased to 7.6%, and the solution had homogeneous distribution and stable properties. But various
functional properties of the composite system reduced when ultrasonic power increased to 450 W due to the occurrence of
insoluble protein aggregate. Thus, the interaction between soybean protein isolate and lecithin became weaker, indicating
that ultrasonication had an impact on soybean protein isolate-phospholipid interaction. Ultrasonic processing at appropriate
intensity would promote the functional properties of the composite system.

Key words: ultrasonic processing, soybean protein isolate, phospholipid, spatial structure, functional properties