Valorizing brewers' spent grain into sustainable stabilizers for food-grade Pickering emulsions: effect of sonication on physicochemical and rheological properties

Abstract

Brewers' spent grain, the primary residue obtained after wort extraction in beer manufacturing, represents an underutilized resource with potential for upcycling into functional food materials. Emerging green technologies such as ultrasonication can modify the structural and interfacial properties of plantbased materials, enhancing their functionality in complex food systems. This study investigated the use of whole brewers' spent grain particles as sustainable stabilizers for Pickering emulsions, with a focus on their structure–function relationships. Brewers' spent grain flour was characterized for chemical composition, and aqueous dispersions were prepared, either untreated (BSG) or ultrasonicated (BSG-S). Both dispersions were evaluated for particle size, ζ-potential, soluble protein content, and microstructure. Coarse oil-in-water Pickering emulsions were formulated using 5%, 7%, and 9% (w/v) BSG or BSG-S as stabilizing particles. Ultrasonication significantly modified the physicochemical features of brewers' spent grain, reducing particle size, increasing surface charge, and enhancing the release of soluble proteins, thereby improving interfacial functionality. Emulsions stabilized with BSG-S displayed smaller and more uniform droplets, with droplet size decreasing as the stabilizer concentration increased. These systems also exhibited a lower creaming index and maintained physical stability for over 24 h. Rheological measurements confirmed a shear-thinning behavior, with increased viscosity at higher particle concentrations, which contributes to the emulsion's structuring. This work highlights minimally processed brewers' spent grain as a low-cost, upcycled, and efficient Pickering stabilizer, offering a promising route toward the development of sustainable food materials and circular economy practices.