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.

In this study, the structural changes and reconstruction mechanism of sesame protein-derived amyloid fibrils under varied digestive parameters (pepsin concentration, digestive pH and ionic strength) during gastric digestion were investigated, and the effect of fibril reconstruction on the gastric digestion stability of β-carotene nanoparticles was also explored. The results demonstrated that amyloid fibrils underwent a three-stage dynamic process of enzymatic hydrolysis, regeneration and degradation during gastric digestion. The pepsin concentration of 2 mg/mL was found to promote the balance between fibril hydrolysis and regeneration. The fibrils displayed a pronounced regenerative capacity at pH values of 1.5 and 2.5, whereas at pH 3.5, which was proximal to the isoelectric point of protein, aggregation and precipitation were observed. Furthermore, it was found that 10 mM NaCl exerted minimal influence on fibril stability, whereas the higher concentrations of salt ions were shown to obstruct regeneration and promote aggregation. Analyses through SDS-PAGE, GPC, and MALDI-TOF-MS revealed a gradual reduction in the molecular weight of the fibrils during gastric digestion, with certain fragments reaggregating to form new fibril structures. The fibril-based delivery system formed a stable protective structure for β-carotene nanoparticles, which not only prevented their aggregation but also facilitated their release in the small intestine.