Enzymatic cross-linking chemical modification and ultrasound to improve the structural and functional properties of soy protein isolate.

Soy protein isolate (SPI) is widely used as a plant protein ingredient. This study modified SPI by ultrasound-assisted laccase treatment (U + La; 150, 300, 450, and 600 W), evaluated its functional properties, and further analyzed the related physicochemical and structural changes. SPI treated with 300 W ultrasound and laccase (UL3) showed the best overall functionality, with the highest water-holding capacity (93.39%), emulsion stability index (42.60 ± 2.24 min), and foaming capacity (169.29%). UL3 also showed a relatively small particle size (362.80 nm) and the highest absolute zeta potential (27.78 mV). Electrophoretic and chromatographic analyses indicated increased high-molecular-weight aggregates after U + La treatment. Spectroscopic and microstructural results suggested that moderate U + La treatment was associated with SPI conformational changes and a compact gel network. Overall, UL3 improved SPI model functionality and showed application potential as a modified plant protein ingredient.