Brazilian Microalgae-Derived Bioactives: Antioxidant and Antibacterial Properties for Skin Care Application

Brazilian microalgae represent an underexplored reservoir of bioactive compounds with promising biotechnological and dermocosmetic applications. In this study, eight native Brazilian microalgae strains were cultivated under control (C) and stress conditions, nitrogen depletion (N) and salt stress (S), to modulate their bioactive profiles. Derived acetone extracts (24 samples) were evaluated for their antioxidant and antibacterial activities relevant to skin health. The antioxidant capacity of extracts was assessed by three complementary methods: ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and superoxide anion radicals scavenging. Additionally, the antibacterial effects against four skin microorganisms (Staphylococcus epidermidis, Staphylococcus hominis, Staphylococcus aureus, and Cutibacterium acnes) were also assessed. Among the tested samples, extracts from Scenedesmus armatus (Extract 40C) and from Chlorella sorokiniana (Extract 198C) displayed the highest antioxidant potential, with DPPH radical reduction of 22.6 ± 1.6% and 20.7 ± 1.9% and FRAP values of 178.3 and 156.8 μmol FeSO4/g extract, respectively. Superoxide scavenging assays showed IC50 values of 150.9 μg/mL for sample 40C and 139.6 μg/mL for sample 198C. Regarding the antibacterial assay, the IC50 values for S. epidermidis were notable, with sample 198C exhibiting the highest potency (10.3 µg/mL), closely matching the standard drug (12.4 µg/mL). The inhibitory capacity against C. acnes showed that samples 40C (58.4 µg/mL) and 198C (83.5 µg/mL) demonstrated antimicrobial relevance. Mechanistic assays suggested that the antibacterial effects of both samples may involve alterations in bacterial membrane integrity and DNA damage. Overall, these findings highlight the dermocosmetic potential of native Brazilian microalgae, still largely untapped in biotechnology, as natural sources of multifunctional ingredients for the development of sustainable skin care formulations.