Valorization of brewer's spent grains (BSG) through alkaline hydrogen peroxide processing: Effect on composition, structure and rheological properties

Abstract

This study investigated the impact of alkaline processing with hydrogen peroxide (AHP) on the chemical composition, structure, and rheological properties of brewer's spent grains (BSG). Suspensions with different concentrations of BSG (2–8 %) and AHP (1–8 %) were subjected to different processing times (0–12 h). The BSG chemical composition, morphology, crystallinity, modifications of functional groups, and rheological behavior were evaluated over processing. Increasing the concentration of AHP in the suspension and the processing time improved the removal of proteins, lignin, and extractives from BSG into the suspension and, consequently, increased the cellulose and hemicellulose content in the processed BSG. On the other hand, higher concentrations of BSG in the suspension slightly reduced the removal efficiency of these components. AHP processing also induced thinning of the cell wall and changes in particle shape. These changes together with the increase in crystallinity of the processed BSG indicated the material destructuring. FTIR spectra showed reduced intensity of lignin and protein post-processing, indicating their removal, while peaks related to cellulose and hemicellulose increased in processed BSG. The flow curves of the suspensions were adjusted to the Herschel-Bulkley model, exhibiting non-Newtonian behavior with flow yield stress (1.529 Pa < τ₀ < 4.646 Pa) and pseudoplasticity (0.830 < n < 0.969) in all conditions. Flow resistance increased with increasing concentration of AHP, BSG, and processing time. Notably, the increase in processing time resulted in greater removal of BSG components, especially proteins, lignin, and extractives, which significantly contributed to the increase in both the flow yield stress and the consistency index of the suspensions. All this information is useful and will support the design of equipment and processes, especially those involving the extraction of proteins and the conversion of the BSG lignocellulose fraction into biofuels.