Reduced-pressure alkaline pretreatment as an innovative and sustainable technology to extract protein from brewer's spent grain

One of the bottlenecks related to the extraction of protein from lignocellulosic biomass is the development of an efficient, selective, economical, and environmentally friendly process. This study investigated the reduced-pressure alkaline pretreatment (RPAP) as an innovative approach for protein extraction from brewer's spent grain (BSG). Experiments were carried out at different temperatures (30–70 °C), pressures (150–1025 mBar), times (1–7 h), and NaOH concentrations (20–180 mM) to obtain a high-yield and selective protein extraction associated with low CO₂ emissions and high processing capacity per batch. Protein concentration, total CO2 emissions per protein extracted, selectivity (related to sugars), and processing capacity were the responses considered for optimization. The optimum condition (T = 70 °C; P = 455 mBar, t = 1 h, and [NaOH] = 180.00 mM) was able to extract 80% of the total protein present in BSG composition. This condition was also selective (76.8%) and had a low carbon footprint (0.43 g CO₂ g _{protein extracted}⁻¹). Glutamic acid was the most abundant amino acid in both raw BSG (22.9%) and protein hydrolysate (23.4%), followed by leucine (9.3% and 7.0%, respectively), proline (8.3% and 11.2%, respectively), and aspartic acid (8.8% and 7.6%, respectively). RPAP was demonstrated to be an efficient and sustainable technology for protein extraction from BSG. This opens up new opportunities for BSG and other protein-rich lignocellulosic materials valorization in a biorefinery.