| A study was carried out aimed at developing a stand-alone, pilot-scale, hydrothermal process that may significantly modify some functional properties of wheat gluten under typical industrial processing conditions. Wheat gluten isolate (WGI), the purest commercially-available form of wheat gluten (>90% protein) was used. Four processing variables were investigated in a split-split-split-plot design: Slurry concentration (9.1%, 12.3%, and 15.3% w/w); processing temperature (121.1°, 135.0°, and 148.9°C); residence time (34 s, 64 s, and 92 s); and method of drying (Spray-Drying, and Freeze-Drying) were the whole plot, sub-plot, sub-sub-plot, and sub-sub-sub-plot, respectively. Each slurry, a blend of WGI with distilled water, was jet-cooked at a desired temperature, held at that temperature for a desired residence time, and cooled rapidly (within 20 s) to 37.8°C. The slurries were then dried to a final moisture content of 5–6% (w.b.), and freeze-dried samples were ground to powder form. Three functional properties: viscosity; water-solubility; and emulsifying capacity (EC); were used to compare treatments.; HPLC profiles of the processed samples revealed polymerization of gliadin molecules (through aggregation and/or cross-linking) to give glutenin or glutenin-like molecules, the extent of polymerization depending on process severity. Viscosity, partly dependent on hydrodynamic properties of the dissolved molecules, and partly on volume fraction, swelling, stiffness and cohesion of undissolved particles, was maximum when a 15.3% w/w WGI slurry was processed at 148.9°C for 92 s and spray-dried. Solubility and EC, both dependent on surface-related properties of the molecules, were maximum when a 9.1% w/w WGI slurry was processed at 148.9°C for 34 s and spray-dried. Under these optimum conditions, viscosity increased significantly by 213.7% compared to the control, control taken as 100% in all comparisons. However, solubility increased insignificantly by 14.4% compared to the control, while EC increased slightly, but statistically significantly, by 5.9% compared to the control. It was concluded that, with minor improvements and refinements, the developed process is capable of offering a simple and user-friendly alternative of modifying some functional properties of wheat gluten isolate. |
