Sustainable Extraction of Bioactive Peptides from Brewery Spent Grain

Brewery spent grain (BSG), the primary by-product of beer production, accounts for 85% of brewing waste. Composed of residual husks, pericarp, and seed coats, BSG is rich in dietary fiber, proteins, and bioactive compounds. While traditionally used as animal feed, it is now being explored for sustainable and circular economy applications, including food, bioethanol, biogas, and bioplastics production. As part of the AGRILOOP EU project, this study investigated BSG for the recovery of proteins and bioactive peptides for food and packaging. Protein analysis with the Kjeldahl method revealed 28% (w/w) protein content in dried BSG. To enhance protein recovery, enzymatic digestions were carried out using Bromelain, Protamex®, and Trypsin at a ratio of 5% (w/w) enzyme/gDW of BSG. Protease treatments and control thermal digestion significantly improved protein release compared to the undigested sample. Additionally, protein solubilizations were conducted under alkaline (NaOH, pH 11) or neutral (phosphate buffer, pH 7.2) conditions, followed by acidic precipitation (pH 3). The low protein precipitation and high peptide concentrations detected in the supernatant suggest that they originate from hydrolysis during the beer malting process. Further analyses on digestates evaluated total phenolic and reducing sugar contents, as well as antioxidant and anti-tyrosinase activities. This study highlights BSG as a valuable source of proteins and bioactive peptides with potential applications across various industries. Transforming BSG into high-value products could contribute to reduce waste and promote circular bioeconomy practices, enhancing sustainability within the brewing industry.