Phytochemical Profiling and Bioefficacy of Macroalgae Extracts Enhanced with ZnO Nanocomposites

Abstract

Combining marine macroalgae with metal nanoparticles presents a viable way to increase the therapeutic potential of these valuable natural bioactive chemicals. This study aimed to investigate the potential of Zinc oxide (ZnO) nanoparticles synthesized using marine macroalgae to enhance the antimicrobial, antioxidant and anti-inflammatory activities of the algal extracts, and to compare these effects across different algal species. Methanolic extracts from macroalgae Gelidium sp. (SB1), Sargassum ilicifolium (SB2), Turbinaria ornata (SB3), and Cladophora sp. (SB4) collected from marine habitats from Sri Lanka and their ZnO composites (named as SB1+ ZnO accordingly) were evaluated for antioxidant (DPPH and Folin–Ciocalteu Assay), anti-inflammatory, and antibacterial (using agar well method and MIC/MBC assay) properties. Glycosides, steroids, and flavonoids, in the algae samples were identified by phytochemical screening. Phenols and tannins were only presented in SB2 and SB4. The ZnO composite of SB2 exhibited the highest phenolic content (0.488 mg GAE/g), which was elevated to 0.604 mg GAE/g in SB4+ ZnO. In SB2+ZnO, a 33% increment in Anti-inflammatory activity was observed at 1600 μg/mL, and antioxidant activity was enhanced in SB2+ZnO (IC₅₀ ≈230 μg/mL) which was at 672 μg/mL in SB2. With MICs ranging from 20 to 40 μg/mL, ZnO and ZnO–algae composites demonstrated antibacterial efficacy against S. aureus, E. coli, P. aeruginosa, and K. pneumoniae (zones: 10–14.8 mm). Given the improved bioactivities, our results demonstrate the potential of S. ilicifolium and T. ornata as well as their ZnO composites, to be used incosmeceutical and pharmaceutical industries.