Valorization of brewer's spent grain for sustainable food packaging

The accumulation of petroleum-based plastics causes economic and environmental concerns which necessitate a comprehensive search for biodegradable packaging materials. Brewer's spent grain (BSG) is an interesting by-product, which is one of the main wastes of beer production in Europe. BSG could offer added value in the food packaging sector owing to the significant amount generated annually, high biomaterials content, and low market value. Herein, the significance of various biorefinery techniques (physical, chemical, and biological) for the extraction of high-value products (such as protein, cellulose, hemicellulose, lignin, and phenolic compounds) from the BSG are comprehensively examined. BSG-derived biodegradable films and coatings for food packaging are critically evaluated. Finally, techno-economics, environmental impacts, energy consumption, regulations, challenges, and prospects are also critically evaluated. The best biorefinery system necessitates a balance between extraction efficiency, energy consumption, environmental impact, tangible upscaling, and operating cost. The mechanical dewatering of BSG before extraction, including the physical pretreatments, utilization of green solvents, the integration of the solvent recovery system, and the combination of two or more biorefinery techniques could reduce the energy requirements, greenhouse gas emissions, and increase the recovery yield of biomaterials. Cellulose, lignin, xylitol, and arabinoxylan are recommended as the most promising components from BSG for food packaging applications.