Development of brewer’s spent grain-derived bio nanocomposites through a multiproduct biorefinery approach for food packaging

Brewer's spent grain (BSG), the by-product of the brewery, serves as a significant reservoir of lignocellulose and protein. In the present work, three fractions rich in protein-lignin (Pr-Lig), hemicellulose (HC), and nanocellulose (NC) were extracted from BSG through a sequential biorefinery process. Then, two distinct composites of Pr-Lig or HC containing various NC content (3, 5, and 7 % wt) were fabricated. The composite properties including surface/chemical structures, moisture sensitivity, tensile, optical, and bioactive properties were then assessed. Results showed that HC-based film possessed higher tensile strength (5.2 MPa), Youngs’ modulus (45 MPa), water vapor permeability (0.83×10−10 g m−1 s−1 Pa−1), and water solubility (79.75 %) than Pr-Lig-based composites. Conversely, the Pr-Lig-based composite exhibited higher ultraviolet barrier, DPPH scavenging activity (47.71 %), and antibacterial activity against Escherichia coli (21.03 %) and Staphylococcus aureus (63.67 %) due to the presence of polyphenolic lignin. The inclusion of NC resulted in significant improvements in water vapor barrier (18.07 and 41.30 %), water solubility (16.13 and 14.83 %), tensile strength (57.21 and 61.90 %), and Young’s modulus (201.84 and 170.13 %) of both HC and Pr-Lig composites, respectively due to the crystalline nature of NC and the potential hydrogen bonding. Nevertheless, the elongation of the Pr-Lig nanocomposite was reduced by 45.83 % after the inclusion of NC. Investigation of the freshness indexes of blueberries coated by BSG-derived composites indicated a significant preservation effect by delaying fruit decay and prolonging the shelf life for 12 days. This study contributes to advancing the sustainable materials and packaging domain by highlighting a cascade biorefinery of lignocellulosic biomass and showcasing the potential of BSG as a valuable resource to develop active packaging. Further investigations into environmental assessments at various stages of biorefinery, fabrication, and end-of-life, compared to conventional plastics, along with safety analyses, can contribute to broadening the application of BSG-derived composites in various fields.