Biopolymeric Melanoidins Capped ZnO Nanocomposites: A New Hybrid Material with UV Blocking and Suppressed Photocatalytic Properties for Sunscreen Action

Sunscreens have emerged as an indispensable tool to combat the dreadful effects of ultraviolet (UV) radiation. However, the photocatalytic behaviour, toxicity, efficiency and white-cast phenomena have been a concern that needs immediate attention. To address this issue, twenty amino acids were reacted with Xylose individually through the Maillard reaction. The resultant polymeric melanoidins were tested for its UV absorption. The highest UV absorption was observed for Xylose–Serine combination. The process parameters were optimized for maximum melanoidins formation using this combination, and melanoidins capped-ZnO nanocomposites (Mel@ZnO) were synthesized through facile hydrothermal condensation reaction. The synthesized Mel@ZnO were characterized using UV–Vis–NIR, FT-IR, DLS-Zeta potential, XRD, HR-TEM–EDX and TGA. The HR-TEM–EDX revealed that Mel@ZnO were spherical with an average particle size of 48.52 ± 16 nm. The as-synthesized Mel@ZnO displayed remarkable antioxidant potential with low IC₅₀ values. The antibacterial potentials were outstanding against gram-positive S. aureus and gram-negative E. coli. Also, Mel@ZnO displayed an attenuated photocatalytic behaviour. The nanocomposite also showed excellent stability for 6 months in various physiological solutions. The outstanding Sun Protection Factor (SPF) of 138 at 25% (w/w) with a broad-spectrum coverage in the UV (290–400 nm) region proves that this novel Mel@ZnO is a potential candidature manifesting as a sunscreen.