Corn Starch-Based Bio-Composite Films Reinforced with Sunflower Seed Hull Powder and Thyme Essential Oil: Enhanced Mechanical, Antioxidant, and Antibacterial Performance for Sustainable Active Food Packaging

Abstract

Engineering biodegradable sheets with inherent bioactivity is a crucial advancement for next-generation active packaging systems. Corn starch-based bio-composite films were enhanced with sunflower seed hull (SSH) powder as a phenolic-rich reinforcement, glycerol as plasticizer, vinegar as an acidic formulation ingredient and thyme essential oil as a bioactive antimicrobial component, facilitating concurrent antioxidant and antibacterial efficacy. Films were produced using solution casting with differing SSH concentrations (0.25-1g). SSH incorporation improved the physicochemical, mechanical, antioxidant, and antibacterial properties of the developed films. Film thickness progressively increased from 0.024 mm to 0.042 mm in SSHT4, density decreased from 0.78 g/cm3 to 0.58g/ cm3 with increasing filler concentration and moisture content reduced from 13.44% to 8.89% in SSHT4, indicating reduced hydrophilicity of the films. Water absorption after 3h immersion reduced from 89.84% to 62.56% in SSHT4, demonstrating reduced water uptake. Tensile strength peaked at 15.94 MPa and elongation at break reached 42.67% in SSHT2 film. SEM- based morphological study demonstrated enhanced dispersion and structural integrity at modest filler loading; ATR-FTIR spectroscopy demonstrated intermolecular interaction and hydrogen bonding between the starch matrix and the SSH component. Antibacterial activity against Staphylococcus aureus and Escherichia coli, showed maximum inhibition zones of 14.5± 1.23mm and 12.5±0.62mm, at SSHT2. DPPH antioxidant activity increased from 28.15mg/mL AAE in the control film to 41.19 mg/mL AAE in SSHT2 films. Biodegradability over 14 days ranged from 82.76% to 65.22% at SSHT4. A single, non-replicated visual shelf-life trial using bread suggested delayed spoilage and better quality retention with SSHT2 film packaging, an observation that requires replicated, quantitative validation before being generalized. Because all SSH-containing formulations also contained thyme essential oil while the control contained neither, the antioxidant and antibacterial improvements reported here cannot be attributed to hull reinforcement alone, and reported values represent measurements taken from a single cast film per formulation. Overall, SSH-based bio-composite films demonstrate strong potential as multifunctional, eco-friendly alternatives to traditional food packaging systems.