Brewery Waste to Functional Food: Alkaline and Ultrasonic Recovery of Brewer's Spent Grain Protein and Its Application in Croissant Fortification

Brewer's spent grain (BSG) is the primary solid by-product of beer production, constituting approximately 85% of total brewery waste yet containing 15–30% protein on a dry weight basis. Despite its nutritional potential BSG is largely directed to low-value applications. This study aimed to valorize BSG through systematic protein extraction and functional food application. This study investigated alkaline and ultrasonic assisted (UAE) techniques to improve protein recovery from BSG.  Alkaline extraction process was performed with sodium hydroxide (NaOH) and potassium hydroxide (KOH) different concentrations (0.1–8 M) while the UAE was carried out under sonication amplitude (20–60 µm) and time (5–25 mins). Recovered proetins extracts were chacterized for protein concentration (Bradford assay), crude protein content (combustion method), and functional properties including water/oil holding capacity and  emulsification properties. The optimizied UAE protein extract was incoporated into two croissnt formulations containing and lacking yeast, while two corresponding control formulations without protein extract were prepared. Croissants were evaluated for protein, moisture, ash, fat, carbohydrate, and energy content usisng standard AOAC methods. Results were analyzed using one-way analysis of variance (ANOVA) for extraction, functional property, and compositional data, with satistical significance established at p < 0.05.  Moderate alkali concentrations (0.1 M KOH and NaOH) produced the highest protein recovery (49 and 59%), whereas 4 M KOH yielded the highest protein concentration (2.35 mg/mL). Further increase in alkalinity reduced protein recovery, likely due to protein degradation. Ultrasound-assisted extraction (UAE) at modified conditions (50 µm amplitude, 15 min) achieved protein recovery of 98% with a crude protein content of 24.04%. UAE-extracted proteins demonstrated excellent functional properties , with a  WHC of 5.77 g/g, OHC  of 4.88 g/g, and EAI of 46 m²/g, and ESI of 98%. Fortification of croissants with UAE derived BSG protein extract (15 g per 200 g flour) significantly increased (p< 0.05) protein content from 4.28 g to 8.39 g and doubled ash content from 0.6 g to 1.2 g. Carbohydrate content declined from 56.02 g to 48.44 g due to protein dilution and yeast-mediated fermentation during processing. These findings establish a scientifically grounded, scalable pathway for converting brewery waste into functional food ingredient with significant implications for sustainable food systems and protein security.