Valorization of Brewing By-Products for Sustainable Active Material

Brewer's spent grain (BSG), the main by-product of the brewing industry, is an abundant lignocellulosic residue that remains underused. In this study, antioxidant-rich extracts were obtained from BSG using pressurized liquid extraction (PLE) and subsequently incorporated into thermoplastic starch (TPS) films for sustainable food packaging applications. The phenolic profile analysis revealed 13 compounds, with caffeic acid and its hexoside as the most abundant. Extraction conditions were optimized using response surface methodology (RSM) to maximize yield and total phenolic content, showing that temperature had a significant positive effect. The selected extract had a total phenolic content of 3.19 mg/g dw and exhibited notable antioxidant activity. It was then incorporated into the polymer matrix, and the resulting films were analyzed for their structural, thermal, and antioxidant properties. The incorporation of BSG extracts improved the film antioxidant activity. Additionally, the release of phenolic compounds was evaluated and successfully described using a diffusion model based on Fick's law, which allowed the calculation of a diffusion coefficient D = 2.63 × 10^-8 cm²/s. Overall, the findings indicate that BSG-based extracts may represent promising functional additives for biodegradable polymer films, and the developed TPS films serve as proof-of-concept active packaging materials from renewable agro-industrial residues.