Mechanism for refunctionalizing heat‐denatured soy protein by alkaline hydrothermal cooking

Abstract

AbstractUsing extrusion heat‐denatured soy protein isolate (SPI) as a model, the mechanism for refunctionalizing heat‐denatured soy protein by hydrothermal cooking (HTC) with alkali was studied. Heating causes soluble protein to form insoluble protein aggregates. Treating heat‐denatured soy protein with alkali dispersion without HTC increased solubility and viscosity by dissolution of a portion of the protein aggregates and swelling of the large protein particles. This suspension was more stable to solid separation than that of the original untreated heat‐denatured protein, but it was less stable than the protein suspensions that were refunctionalized by water dispersion with HTC or alkali dispersion with HTC. Water dispersion with HTC disrupted the large aggregates into smaller aggregates. The viscosity and total number of particles in the system also increased dramatically. The most significant effect was achieved with alkali dispersion (0.6 mmol NaOH/g) with HTC. The solubility increased from 4 to about 80% at neutral pH, and viscosity (at zero shear rate) increased by more than 1,000 times compared with extrusion heat‐denatured SPI. Alkali dispersion (0.6 mmol NaOH/g) with HTC dissolved most of the protein particles, decreasing the particle number by a factor of almost 100. The suspensions of heat‐denatured soy protein became much more stable after HTC as shown by particle settling velocities. The most effective treatment was alkali dispersion (0.6 mmol NaOH/g) with HTC, followed by water dispersion with HTC. The soy protein slurry refunctionalized by alkali dispersion (0.6 mmol NaOH/g) with HTC formed soft, translucent gels.