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 m ² /g; FP: 16.24 ± 0.34 m ² /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.