From brewer's spent grain protein to edible coatings: Extraction, characterization and application in blueberry preservation

Brewer's spent grain (BSG) is a protein-riched by-product with high utilization potential. Herein, this study developed a sequential extraction strategy (integrating enzymatic pre-treatment with ultrasound-assisted alkaline extraction) to facilitate the high-efficiency recovery of BSG protein (BSGP). The impact of various operating parameters on the structural, functional and film-forming properties of extracted proteins was evaluated. Under the optimal extraction conditions (alkali-extracted at pH 12.5, 60 °C, acid-precipitated at pH 4.0, ultrasound at 450 W for 30 min, and an enzyme blender of endo-protease, β-glucanase and xylanase), BSGP with the highest protein yield and purity (78.6% and 75.0%, respectively) was achieved. Structural characterization revealed that ultrasound improved hydrophobicity and emulsifying stability, while enzymolysis enhanced solubility and antioxidant activity. Edible films prepared from ultrasound-extracted BSGP (S3) exhibited a relatively smoother surface, lower water vapor permeability and greater total phenolic content. When applied as coatings, the BSGP-based films notably reduced weight loss, microbial growth and decay incidence of blueberries during storage.