Effects of High Pressure and Heat Treatments on Physicochemical and Gelation Properties of Rapeseed Protein Isolate

High pressure (HP, 200, 400, and 600 MPa)- and heat (60, 80, and 100 A degrees C)-induced gelation, aggregation, and structural conformations of rapeseed protein isolate (RPI) were characterized using gel permeation-size-exclusion chromatography, differential scanning calorimetry, and circular dichroism (CD) techniques. HP treatments significantly (p < 0.05) increased the content of soluble protein aggregates and surface hydrophobicity of RPI. In contrast, heat treatments at 80 and 100 A degrees C led to significant (p < 0.05) decreases in the amount of soluble protein aggregates. At pressure treatment of 200 MPa, there was a significant (p < 0.05) increase in free sulfhydryl group content of RPI, whereas 400- and 600-MPa treatments as well as temperature treatments (60-100 A degrees C) caused significant decreases. Protein denaturation temperature was increased by about 6 A degrees C by HP and heat treatments. The far-UV CD spectra revealed increases in alpha-helix content of RPI after HP treatments with 400 MPa producing the most increase. Near-UV data showed that HP and heat treatments of RPI led to increasing interactions among the aromatic amino acids (evidence of protein aggregation), and between aromatic amino acids and the hydrophilic environment, which indicates protein unfolding. Least gelation concentration of RPI was significantly (p < 0.05) reduced by HP and heat treatments, but HP-treated RPI produced gels with better textural properties (hardness increased from similar to 7.7 to 81.1 N, while springiness increased from similar to 0.37 to 0.99). Overall, pressure treatments (200-600 MPa) were better than heat treatments (60-100 A degrees C) to modify the structure and improve gelation properties of RPI.