Abstract
The objective of this study was to investigate the effects of different high-intensity ultrasonication (HIU) pretreatment on the structure and properties of soybean protein isolate (SPI) as well as enzymatic hydrolysis of SPI by bromelain and antioxidant activity of hydrolysates. The HIU-treated SPI fractions showed a decrease in the proportion of α-helices and β-turns and an increase in the content of β-sheets and random coils based on Fourier-transform infrared spectroscopy. Near-infrared spectra and fluorescence spectra analyses provided support for the changes in secondary and tertiary structures of SPI after ultrasound treatment. The particle size of SPI decreased from 217.20 nm to 141.23 nm and the absolute zeta potential increased. Scanning electron microscopy showed that HIU treatment changed apparent morphology. Dynamic and static light scattering of ultrasonicated samples showed that SPI structure had changed from hard-sphere to hollow-sphere or polydisperse and monodisperse gaussian coils. HIU pretreatment significantly increased the hydroxyl-radical scavenging and the degree of hydrolysis of the SPI hydrolysates.
Highlights
Protein is an important component of human nutrition and proteins play different roles in functional food
We studied the enhancement of enzymatic hydrolysis and antioxidant activities of Soybean protein isolate (SPI) hydrolysates due to high-intensity ultrasonication (HIU) treatment
NIR spectra revealed that the secondary structure of HIU-treated SPI was altered, especially the peak intensities of SH-related bands decreased after ultrasonication indicating that changes in the content of the sulfhydryl group in SPI can be determined by NIR spectra quickly
Summary
Protein is an important component of human nutrition and proteins play different roles in functional food. Soybean protein isolate (SPI) has been extensively used in functional and nutritional food ingredients on account of its low price and high nutritional value. The functional properties are “the chemical and physical properties that affect the interaction between protein and other compounds in the processing, storage, and consumption” [2,3]. These properties are influenced by various factors: heating, pH, ionic strength, and chemical, physical, or enzymatic modification. Most studies focus on combining various modification methods to improve the functional features of proteins [4,5,6]
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