Properties of Isolated, Thermally Induced Soy Protein Fibrillar Aggregates
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Abstract:
Soy protein isolate (SPI) spontaneously forms fibrillar aggregates under acidic heat treatment; however, certain peptides still do not self-assemble into aggregates and the ratio between fibrillar aggregates and peptides has a great impact on functional properties of the protein. Fibrillar aggregates and peptides were separated in bulk by ultrafiltration, in order to study their physicochemical properties. The results showed that 100 ku ultrafiltration membrane can produce a good separation effect after two separation cycles. After heat treatment, SPI solubility at the isoelectric point increased, but that at neutral pH decreased. Additionally, protein hydrolysis caused the absolute value of the surface potential to increase. Amino acid composition and surface potential of fibrillar aggregates were similar to those of heated SPI, but its solubility at isoelectric point and neutral pH decreased significantly. Peptides contained fewer hydrophobic amino acids and more negatively charged amino acids; solubility at pH 2.0 to 9.0 was relatively higher, while the electric charge and electrostatic repulsive force were lower at acidic pH, leading to the amorphous formation of aggregates. Thus, high charge at neutral pH results in weakened interactions among peptides and the dissociation of amorphous aggregates.
