Microbial Fermentation Potentiates the Multifunctional Skin-Care Activities of Polianthes tuberosa L. Flower Extract: Antioxidant, Anti-Glycation, and Anti-Melanogenic Effects

Polianthes tuberosa L. (PT) flower extracts exhibit considerable bioactivities, yet their application is often constrained by limited bioavailability and efficacy. In this study, fermentation of PT (FPT) using Rhodosporidium toruloides significantly enhanced its phytochemical profile, doubling the total phenol content (697.22 ± 7.51 μg/mL in FPT versus (vs.) 347.61 ± 5.89 μg/mL in non-fermented extract (NF)) and increasing flavonoids by onefold relative to NF (381.44 ± 6.50 μg/mL in FPT vs. 190.25 ± 4.75 μg/mL in NF), resulting in a substantial improvement in radical scavenging capacity (DPPH: 47.59 ± 1.55%; ABTS: 89.87 ± 1.39%). In UVB-irradiated the human keratinocyte cell line, FPT demonstrated superior efficacy over NF by effectively reducing reactive oxygen species and malondialdehyde levels (1.29 ± 0.08 ng/mL at 0.4 mg/mL FPT vs. 1.5 ± 0.1 ng/mL with NF), while concurrently elevating the activity of key antioxidant enzymes. Using human dermal fibroblasts, FPT was further shown to possess notable anti-glycation and anti-carbonylation properties, significantly inhibiting carboxymethyl lysine formation (90.6 ± 3.6% reduction) and protein carbonylation (86.5 ± 2.2% reduction). It also suppressed senescence-associated β-galactosidase activity (67.9 ± 3.0% inhibition), downregulated matrix metalloproteinase-1 expression (62.5 ± 5.1% reduction), and stimulated type I collagen synthesis (166.5 ± 4.2% recovery). Additionally, FPT markedly inhibited UVB-induced melanogenesis in B16F10 melanoma cells by reducing melanin content (36.0 ± 5.3%) and tyrosinase activity (45.7 ± 1.2%), through the downregulation of critical melanogenic genes, including melanocortin 1 receptor, microphthalmia-associated transcription factor, and tyrosinase.