Extraction Techniques for Brewer's Spent Grain Protein: A Comparative Review of Efficiency, Purity, and Functionality

Brewer's spent grain (BSG), the primary by-product of beer production, represents a promising and sustainable source of plant-based protein. This review provides a comprehensive overview of extraction techniques for brewer's spent grain protein (BSGP), encompassing conventional methods-such as alkaline, hydrothermal, ethanol, and enzymatic extraction-as well as emerging green approaches, including ultrasound-assisted, microwave-assisted, subcritical water, and deep eutectic solvent extraction. The influence of key extraction parameters on protein yield, purity, and structural integrity is critically examined, along with the resultant alterations in functional properties such as solubility, emulsifying capacity, foaming ability, and gelation behavior. Although through parameter optimization and the application of novel technology, the existing research has been able to increase the protein extraction rate and achieve better functional properties, the challenges of obtaining higher protein purity and extracting proteins on a larger scale remain. Collectively, these findings underscore the considerable potential of BSGP as a multifunctional ingredient in next-generation sustainable food formulations.