Solubility, Heat-Induced Gelation and Pepsin Susceptibility of Cruciferin Protein as Affected by Subunit Composition

摘要

This study examined the solubility, heat-induced gel formation ability, and pepsin susceptibility of cruciferin with mixed (wild type, WT) or identical subunits (CRUA, CRUB, or CRUC). All cruciferin species exhibited minimal solubility at pH 4.0 and slight solubility between pH 7.5 and 8, which was not influenced by the presence of NaCl. Increasing temperature to 90 A degrees C did not affect the solubility of CRUC, but affected the solubility of other cruciferins between pH 4.0 and 8.0. Changes of secondary structure of cruciferins in a range of pH suggested structural alterations of the hexameric assembly might occur at pH 2.0. Near neutral pH was suitable to form heat-induced gels of WT, CRUA, and CRUB species. Although pH 2.0 was suitable for CRUC to form a strong gel, the same pH inhibited CRUB gel formation. High salt content (0.5 M NaCl) at neutral pH did not change the gel formation ability of WT, CRUA, or CRUB, but affected the gel characteristics. All cruciferins were hydrolyzed by pepsin, but the CRUC was degraded at a slower rate than the others. Trimer surface characteristics and the orientation and interaction of the HVR-I region of the hexameric assembly could be main structural factors for these property differences. Although the CRUC subunit showed properties that deviated from other species, the influence of CRUA and CRUB subunits seemed more prominent in the mixed subunit hexamer of WT.