Effect of Ultrasound Treatment on the Physicochemical and Functional Properties of Brewer’s Spent Grain Protein Extracted by Fast Alkali Extraction

Justification: Brewer’s spent grain (BSG), a protein-rich by-product of the brewing industry, offers a sustainable alternative to animal proteins, which raise ethical concerns. However, its functional properties must be modified for industrial use. This study employs fast alkali extraction and ultrasound treatment to enhance BSG protein functionality, making it suitable for plant-based meat applications and meeting the growing demand for sustainable protein sources.

Objective: To assess the effectiveness of fast alkali extraction technique combined with ultrasound treatment in enhancing the functional and structural properties of BSG protein (BSGP).

Methods: BSG was autoclaved, dried at 60°C, milled, and sieved through a 40-mesh screen. After defatting and delignification, it was treated with 0.18% NaOH (w/v) at a 1:15 ratio, stirred at 1000 rpm at 30°C, centrifuged, and protein was precipitated at pH 4.5, and freeze-dried. The BSG protein (BSGP) was characterized for yield and proximate composition. A 6% (w/v) dispersion of freeze-dried BSGP was prepared and underwent ultrasound treatment (20 kHz, 100 W, 4°C, 2s on/1s off) for 5, 15, and 25 minutes. The ultrasound-treated BSGP (US-BSGP) was collected, freeze-dried, and analyzed for FTIR, water retention capacity (WRC), oil retention capacity (ORC), emulsifying activity index (EAI), and emulsifying stability index (ESI).

Results: The yield of BSGP was 4.8±1.2 g protein per 100 g of BSG, with a proximate protein content of 52.2±2.1%. FTIR analysis showed notable differences between untreated and treated BSGP but minimal variation among US-BSGP. The highest WRC (6.91±0.87 g water/g), ORC (2.57±1.07 g oil/g), EAI (82.33±0.61 m²/g), and ESI (13.41±0.82 min) were observed at 15 minutes of ultrasound treatment showing a significant effect of ultrasound treatment on BSGP functional properties.

Significance: Ultrasound enhances BSGP’s functional properties, offering a sustainable, allergen-free protein for plant-based meats, aligning with the AOCS mission to advance eco-friendly protein solutions.