Development and characterization of BSA-pullulan gel matrices incorporating orange peel flavonoids: Structural interactions and antimicrobial and antioxidant functionalities

This study investigates the molecular interactions and functionality of bovine serum albumin-pullulan (BSA-Pn) hydrogels integrated with orange flavonoid extracts (Fs). Structural characterization via vibrational and fluorescence spectroscopies revealed noncovalent interactions, primarily H-bonding, between BSA, pullulan, and flavonoids, as confirmed by molecular docking modelling. Surface chemistry analysis revealed that increased C1s-peak intensity in BSA-Pn-Fs-9 composite, thereby indicating a structural reorganization. The hydrogel demonstrated potent an antimicrobial activity against Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, with inhibition zones of 1.34-1.69 cm, and suppressed fungal growth (Penicillium expansum and Aspergillus westerdijkiae) by 40.72-43.24 %. Thermal stability of flavonoids within matrix was enhanced, as evidenced by thermal structure analysis. Antioxidant assays showed significant radical scavenging with values of 33.49-93.47 % versus free radicals scavenging, confirming preserved flavonoid bioactivity. These findings underscore the structure-function synergy of BSA-Pn-Fs composites, driven by polysaccharide-protein-flavonoid interactions, positioning them as promising candidates for bioactive and functional biomaterials/additives.