Upcycling sorghum grain waste to fabricate a bioactive and biodegradable composite film for food packaging

Abstract The growing environmental burden caused by non-degradable plastics, particularly in food packaging, underscores the urgent need for the development of biodegradable alternatives that can help mitigate pollution. Sorghum grain waste (SGW), a polyphenol-rich residue from the extraction of 3-deoxyanthocyanidins, was incorporated into polyvinyl alcohol (PVA) to fabricate packaging films. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the presence of strong intermolecular hydrogen bonding between SGW and PVA. Scanning electron microscopy (SEM) revealed favorable interfacial compatibility within the composite structure, endowing the film with high thermal stability and considerable tensile strength (tensile strength: 6.37–9.70 MPa; elongation at break: 25.7%–58.3%). The PVA/SGW-20% film exhibited the lowest water vapor permeability (9.34 g/(m·h·Pa)) and water absorption rate (44.31%). The inherent polyphenols within SGW imparted potent bioactive functionalities to the films. The optimized PVA/SGW films exhibited antioxidant activity (62.38% against DPPH; 69.24% against ABTS+) and demonstrated significant antibacterial activity against common foodborne pathogens. Furthermore, the PVA/SGW-20% film had a biodegradation ratio of 56.24% within 15 d in soil. Fresh-cut apple preservation tests demonstrated that the PVA/SGW film significantly extended shelf life by more effectively inhibiting enzymatic browning and moisture loss compared with the pure PVA films. This work provides supporting data for the upcycling of agricultural waste.