Effect of ultrasound treatment on the properties of lotus seed protein gel.

Lotus seed protein, as a plant protein, has high nutritional and functional value but limited gelation ability. So, the structure and gelation properties of lotus seed protein gel (LSPG) treated using ultrasound were investigated. Structural properties were analyzed through surface hydrophobicity, free sulfhydryl groups, electrophoresis, Fourier transform infrared spectroscopy and intermolecular forces. Gelation properties were evaluated through rheology, water-holding capacity (WHC), texture and scanning electron microscopy (SEM). Hydrophobic interactions and disulfide bonds played crucial roles in LSPG formation. Surface hydrophobicity of LSP increased from 484.3 to 1601 AU, but free sulfhydryl content of LSPG decreased from 1.35 (control) to 0.62 μmol g-1 (300 W) with increasing ultrasound power (0-300 W). SDS-PAGE analysis showed that LSPG had eight distinct protein bands of 24, 28, 34, 53, 57, 62, 70 and 140 kDa, of which that at 28 kDa was dominant. Ultrasound treatment did not alter protein subunit composition. Additionally, a shift in secondary structure was observed, with an increase in β-sheet content from 22.21% to 23.48% and a decrease in α-helix content from 28.07% to 26.16%. Observation using SEM indicated that ultrasound-treated LSPG microstructure became denser and more uniform than control. Ultrasound treatment also enhanced the textural properties and WHC of LSPG. Among ultrasound powers of 60, 120, 180, 240 and 300 W, the highest storage modulus (1.61 × 106 Pa), hardness (2556.1 g), chewiness (2129.9), springiness (0.983), cohesiveness (0.864) and WHC (96.2%) were at 180 W. This study provides a theoretical basis for applying LSPG in food processing.