The skin, as the largest organ of the human body, is consistently subjected to environmental stressors like ultraviolet (UV) radiation and pollution. These stressors lead to oxidative stress, which is a primary driver of accelerated skin aging, manifesting as wrinkles, loss of elasticity, and hyperpigmentation. Both oxidative stress and glycation play major roles in skin aging by promoting the accumulation of reactive oxygen species (ROS) and advanced glycation end products (AGEs), ultimately compromising the structural integrity and function of the skin by inhibiting collagen synthesis and exacerbating inflammation.
To counteract these effects safely, plant extracts have garnered significant interest due to their rich natural bioactive compounds offering multiple functions. Polianthes tuberosa L. (PT) flower extracts are known to possess considerable bioactivities, including antioxidant, anti-inflammatory, and antibacterial properties. However, the application of pristine plant extracts is often limited by their low active ingredient content and limited bioavailability and efficacy.
Microbial fermentation technology was considered as a potential solution because it provides an effective strategy to simultaneously enhance the extraction efficiency of target compounds (via enzymatic degradation of plant cell walls) and augment the bioactivity of the extracts by generating low-molecular-weight metabolites. This study thus aimed to screen for an optimal microbial strain for PT fermentation and systematically evaluate the resulting fermented PT extract (FPT) for enhanced antioxidant, anti-glycation, anti-carbonylation, anti-photoaging, and whitening efficacy.
Methods
The optimal strain for PT fermentation was identified by screening ten activated yeast strains based on their ability to enhance total phenols, total flavonoids, and DPPH/ABTS radical scavenging capacities, leading to the selection of Rhodosporidium toruloides. The resulting fermented PT extract (FPT) and the non-fermented extract (NF) were then evaluated for biological activity using multiple cell lines, including human keratinocyte cells (HaCaT), human dermal fibroblasts (HDF), and B16F10 melanoma cells. The efficacy was quantified using various assays measuring oxidative stress biomarkers (e.g., MDA, SOD, CAT), anti-glycation/anti-carbonylation effects (e.g., CML, 5-FTSC staining), anti-aging markers (e.g., SA-β-gal, MMP-1, Col-I, IL-6), and anti-melanogenesis (melanin content, tyrosinase activity, and gene expression). Finally, untargeted metabolomics (UHPLC-Q-TOF MS) was employed to analyze the compositional changes before and after fermentation.
Key Findings
• Fermentation Significantly Enhanced Phytochemical Profile and Antioxidant Capacity: Fermentation with Rhodosporidium toruloides doubled the total phenol content and increased flavonoids by onefold compared to the non-fermented extract (NF), resulting in a substantial improvement in radical scavenging capacity (DPPH: 47.59 ± 1.55%; ABTS: 89.87 ± 1.39%).
• Superior Cytoprotection Against Oxidative Stress: In UVB-irradiated HaCaT cells, FPT demonstrated superior efficacy over NF, effectively reducing reactive oxygen species (ROS) and malondialdehyde (MDA) levels. FPT also showed a significantly greater restorative effect on endogenous antioxidant enzymes (SOD, GSH-Px, and CAT) compared to NF.
• Potent Dual Inhibition of Glycation and Carbonylation: FPT exhibited notable anti-glycation and anti-carbonylation properties in human dermal fibroblasts. FPT significantly inhibited the formation of carboxymethyl lysine (CML, a representative AGE) by 90.6 ± 3.6% and protein carbonylation by 86.5 ± 2.2%, outperforming NF in both assays.
• Effective Anti-Photoaging Activity: FPT effectively combated UVA-induced photoaging. It significantly suppressed senescence-associated β-galactosidase (SA-β-gal) activity, achieving 67.9 ± 3.0% inhibition (superior to NF’s 46.4 ± 4.9%).
• Extracellular Matrix (ECM) Rebalancing: FPT mitigated ECM degradation by down-regulating matrix metalloproteinase-1 (MMP-1) expression (62.5 ± 5.1% reduction) and promoting Type I collagen (Col-I) synthesis, achieving 166.5 ± 4.2% recovery. FPT also demonstrated potent anti-inflammatory activity by suppressing IL-6 secretion by 54.0 ± 2.3%.
• Significant Anti-Melanogenic Effects: FPT markedly inhibited UVB-induced melanogenesis in B16F10 melanoma cells, reducing melanin content by 36.0 ± 5.3% and tyrosinase activity by 45.7 ± 1.2% at the optimal concentration. This whitening effect was attributed to the downregulation of critical melanogenic genes, primarily the MITF signaling axis (including MITF, TYR, TYRP1, and TYRP2).
• Metabolomic Changes Confirmed Bioenhancement: Untargeted metabolomics analysis identified 432 differential metabolites before and after fermentation, including the upregulation of 15 polyphenols. The significant upregulation of phenylpropanoids and flavonoids, such as Amentoflavone, provides the chemical basis for the observed superior efficacy.
This research demonstrates that microbial fermentation profoundly enhances the multifunctional skin-care potential of Polianthes tuberosa L. flower extracts, identifying Rhodosporidium toruloides as the optimal strain for biotransformation. The novelty of this work lies in the successful generation of a fermented extract (FPT) that exhibits a significantly superior biological profile over the non-fermented counterpart across multiple key mechanisms of skin aging and hyperpigmentation. A pivotal finding is the FPT’s ability to provide concurrent and potent inhibition of both glycation and protein carbonylation. Furthermore, untargeted metabolomics provided compelling chemical evidence that the enhanced efficacy is linked to the significant upregulation of bioactive metabolites like phenylpropanoids and flavonoids.
Despite the promising in vitro results, the study highlights several limitations, primarily the reliance solely on cell-based models. Future implications for this research focus on the need for more systematic and in-depth investigations, specifically: comprehensively elucidating the in vivo mechanisms of action, isolating and identifying the specific key active constituents responsible for the observed activities, and evaluating critical formulation properties such as safety, stability, and skin permeation. Exploring potential synergistic effects among the newly generated metabolites could further facilitate the translation of these findings into practical cosmetic and dermatological applications.
Link to the study: https://www.mdpi.com/2079-9284/12/6/243
