Effect of vortex fluidic device and its combined treatment with ultrasonication on the conformational changes of soy protein isolate.

Enhancing the functional properties of Soy Protein Isolate (SPI) is critical for its effective application in the food industry. The present study explored SPI modification through twomethods: (1) varying the rotational speed of a Vortex Fluidic Device (VFD) between 2000 and 8000 rpm, and (2) integrating Ultrasound (US) treatment (40 kHz, 220 V; 10-50 min) in combination with VFD operation at 8000 rpm. VFD treatment reduced substantial particle size (from 1732 nm to 591.6 nm) and increased the denaturation temperature (Tp) to 109.56 °C, indicating enhanced thermal stability. While the secondary structure was largely stable, a specific conformational shift occurred at VFD6000, marked by a ∼6.7 % decrease in β-turns and a ∼2.9 % increase in β-sheets. In contrast, the synergistic USVFD treatment induced more pronounced structural changes; the US30VFD8000 condition increased β-sheet content by ∼7.4 % and promoted re-aggregation (particle size ∼761.5 nm vs. 623.1 nm for VFD8000), albeit with a slight reduction in Tp to 107.79 °C. Thermogravimetric analysis (TGA) confirmed that USVFD accelerated degradation, increasing mass loss to ∼36.7 % (vs. ∼29.4 % for native SPI) and reducing final residue to ∼21.2 % (vs. ∼25.3 % for VFD8000). SEM imaging clearly illustrated these trends, revealing fragmented structures after VFD and uniform aggregates with clusters following USVFD treatment. These findings demonstrate that VFD treatment primarily unfolds and fragments SPI, while USVFD promotes re-aggregation into a modified structure. This provides a strategic basis for tailoring SPI functionality, VFD for thermal stability and USVFD for improved hydration, enabling targeted applications in food design.