EFFECTS OF PROCESSING CONDITIONS AND INGREDIENTS ON THE PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF PEA PROTEIN ISOLATE GELS

The main objectives of this project were to study the rheological and textural properties of heat-induced pea protein isolate (PPI) gels and the effects of processing conditions and microbial transglutaminase (MTGase)on the gels, using chemical and instrumental methods. Physicochemical and gelation properties of commercial pea protein isolate were compared to laboratory prepared PPI with minimal denaturation (designated as native) and to homologoussoy protein isolates (SPI).Four studies were carried out in this research. In the first study, solubility and thermal properties of native and commercial PPI were investigated. Native PPI exhibited higher nitrogen solubility index (NSI) values compared to commercial PPI at pHs higher and lower than the isoelectric point. Differential scanning calorimetry (DSC) of native PPI slurries (10% protein concentration)revealed a single endothermic peak for the globulin fraction. SPI showed separate peaks for conglycinin (7S) and glycinin (11 S). By increasing the NaCI concentration from 0% to 2% (w/w),the denaturation temperature (Td) of the globulin fraction of native PPI was shifted from 85 to 93°C and the Td of the 7S and 11 S fractions of native SPI were increased from 75 to 82°C and from 93 to 100°C, respectively. The globulin protein fractions in commercial PPI and SPI were probably denatured, as DSC of commercial PPI and SPI showed no endothermic peak for the globulin protein fraction and no response to presence of NaCl. When the heating temperature was increased from 82 to 92°C (i.e. higher than the Td of native PPI globulin with 1 % NaCI, w/w, 90°C),a considerable increase in the shear stress of native PPI gels (19.6% protein, 1% NaCI concentration, w/w)was observed. Native PPI gels exhibited lower shear stress and higher shear strain than commercial PPI gels. Slurries of native PPI and SPI (10% protein, w/w) showedno structure development during small oscillation dynamic rheometry when heated from 35 to 75°C. Native PPI showed lower storage modulus (G')values (i.e. less solid-like)after 75°C than did native SPI. Commercial SPI slurries exhibited higher G' values during the complete heating process with a higher degree of initial structure development, than was observed for commercial PPI slurries. In the second study, the effects of process conditions (heating temperature, pH and NaCl level) on the gelation properties of commercial PPI were evaluated using a rotatable response surface design. As heating temperature increased from 79 to 95°C, there was a significant increase in gel shear stress and hardness. Shear strain and cohesiveness of gels were considerably increased (P