热诱导大豆蛋白纤维聚集体的分离及性质研究

酸性热处理条件下,随着大豆分离蛋白(SPI)自发形成纤维聚集体,仍有部分未自组装聚集的多肽分子存在其中,二者比例对蛋白功能性质产生较大影响。本文以超滤手段对热诱导大豆蛋白纤维聚集体和多肽进行大量分离,确定分离方法并研究两者的理化性质。结果表明:100 ku超滤膜反复分离两次即能获得较好的分离效果;SPI经热处理后,其等电点溶解度提高,但中性p H下溶解度变小,且蛋白水解致使其表面电位绝对值明显提高;分离所得纤维聚集体的氨基酸组成和表面电位与热处理蛋白相似,在等电点和中性p H溶解度更低;多肽则含有较少疏水氨基酸和较多负电氨基酸,在p H 2.0~9.0溶解度较好,其在酸性p H下电荷量和静电排斥力较低,导致其以无定形聚集体的形式存在,而中性p H其电荷量较高导致多肽分子间相互作用减弱,聚集体解离。

Properties of Isolated, Thermally Induced Soy Protein Fibrillar Aggregates

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.