Improved Solubility and Functional Properties of Flaxseed Protein Through pH-Shifting Combined With Heat or Ultrasound.

Flaxseed protein (FP), an emerging high-quality plant protein valued for its nutrition, suffers from low solubility at neutral pH. This study employed alkaline (pH 12)-heat treatment (40°C-100°C) or alkaline (pH 12)-ultrasonication (20 kHz, 600 W) to modify FP. The pH-shifting plus ultrasound treatment (20 min; FP12U20) achieved the highest solubility (25.51 ± 0.78 mg/mL), a 144.6% increase over untreated FP (10.43 ± 0.22 mg/mL). In contrast, pH-shifting alone (FP12) yielded 15.02 ± 0.16 mg/mL, and the optimal alkaline-heat treatment (H40T40) reached 16.46 ± 0.54 mg/mL. Modifications also enhanced emulsification and foaming properties, evidenced by increased values for EAI (FP12U20: 50.84 ± 0.45 m²/g; FP: 16.24 ± 0.34 m²/g), ESI at 10 min (FP12U20: 90.51 ± 0.60%; FP: 72.86 ± 0.63%), FA (FP12U20: 113.3 ± 1.12%; FP: 28.66 ± 0.98%), and FS (FP12U20: 97.1 ± 2.86%; FP: 86.04 ± 1.34%). Analysis revealed decreased particle size (FP12U20: 77.21 ± 2.54 nm; FP: 126.22 ± 0.67 nm), increased surface hydrophobicity (FP12U20: 4183 ± 38.11; FP: 1082 ± 138.38), decreased α-helix content (FP12U20: 35.6 ± 1.23%; FP: 46.4 ± 0.88%), and increased β-sheet content (FP12U20: 20.7 ± 0.99%; FP: 13.8 ± 0.69%), suggesting that protein unfolding and hydrophobic exposure were associated with improvements in solubility and functionality. This work establishes a foundation for FP modification using pH-shifting and ultrasound treatments.