Comparative Antioxidant and Antimicrobial Activities of Stem and Root Bark Extracts and Solvent Fractions of Securidaca longepedunculata

Technical Summary: Comparative Antioxidant and Antimicrobial Activities of Securidaca longepedunculata Stem and Root Bark

Problem Statement
Securidaca longepedunculata Fresen is a medicinal plant widely utilized in the traditional medicine of northern Ghana, particularly in the Talensi district, for treating various ailments including inflammatory conditions and microbial infections. While the root bark is the primary part used in local therapeutic regimens, its continuous harvesting leads to the death of the plant, posing a significant threat to the species' sustainability. There is a critical need to identify alternative, sustainable plant parts that retain comparable medicinal efficacy to ensure the conservation of the species while maintaining access to traditional remedies.

Methodology
This study conducted a comparative evaluation of the antioxidant and antimicrobial properties of the stem bark versus the root bark of S. longepedunculata.

• Sample Preparation: Stem and root barks were collected from wild populations in Sheaga, Ghana, authenticated, and processed into dried powders.
• Extraction and Fractionation: Both plant parts were extracted using 70% ethanol. The resulting crude extracts were subsequently partitioned using solvents of increasing polarity: chloroform, ethyl acetate, and butanol, to obtain six distinct fractions (three per plant part).
• Phytochemical Analysis: Qualitative screening was performed for alkaloids, steroids, anthraquinones, cardenolides, saponins, phenolics, flavonoids, cardiac glycosides, tannins, coumarins, and triterpenes. Quantitative analysis determined Total Phenolic Content (TPC) and Total Flavonoid Content (TFC).
• Antioxidant Assays: Total Antioxidant Capacity (TAC) was measured via the phosphomolybdenum method, and radical scavenging activity was assessed using the DPPH assay to calculate IC₅₀ values.
• Antimicrobial Assays: The Flash Microbiocide technique was employed to determine Minimum Bactericidal Concentrations (MBC) and Minimum Fungicidal Concentrations (MFC) against a panel of bacteria (N. gonorrhoeae, S. Typhi, P. aeruginosa, E. coli, S. aureus, S. pyogenes) and the fungus C. albicans.
• Data Analysis: Results were analyzed using ANOVA, and chemometric approaches (correlation matrices, PCA, and Hierarchical Clustering Analysis) were utilized to elucidate relationships between phytochemical profiles and biological activities.

Key Results

• Phytochemical Profile: Both stem and root barks contained similar phytochemical classes (alkaloids, phenolics, flavonoids, etc.), confirming 70% ethanol as an effective broad-spectrum solvent. However, quantitative differences were observed.
• Yield and Composition: The stem bark crude extract yielded slightly less (14.88%) than the root bark (18.32%), but the stem bark fractions generally showed higher yields in the butanol fraction.
• Antioxidant Activity:
  • TPC and TFC: The stem bark consistently exhibited higher phenolic and flavonoid contents than the root bark. Notably, the chloroform fractions of both parts showed the highest TPC and TFC values, with the stem bark chloroform fraction reaching 95.16 mg GAE/g DW (TPC) and 257.55 mg RE/g DW (TFC).
  • TAC and DPPH: The stem bark demonstrated superior antioxidant capacity (251.14 mg AAE/g DW) compared to the root bark (245.38 mg AAE/g DW). In the DPPH assay, the stem bark crude extract had a lower IC₅₀ (0.343 mg/mL) than the root bark (0.491 mg/mL), indicating stronger radical scavenging. The chloroform fractions exhibited the highest activity across both assays.
• Antimicrobial Activity:
  • The stem bark extract demonstrated broad-spectrum activity against all tested microorganisms, whereas the root bark extract was effective only against S. Typhi and N. gonorrhoeae.
  • The stem bark extract showed an activity score of 7 (out of 7 tested organisms), compared to a score of 2 for the root bark.
  • Among fractions, the chloroform and ethyl acetate fractions of the stem bark showed the highest potency. The butanol fractions generally displayed reduced or no activity.
• Chemometric Insights: Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA) confirmed that the chloroform fractions of both plant parts clustered with high antioxidant and antimicrobial activity, driven by low-to-intermediate polarity compounds. The stem bark fractions consistently grouped with higher bioactivity metrics compared to their root counterparts.

Significance and Claims
The paper asserts that the stem bark of S. longepedunculata possesses superior or comparable antioxidant and antimicrobial activities relative to the traditionally harvested root bark. Specifically, the study highlights that:

1. Sustainability: The stem bark is a viable, sustainable alternative to the root bark. Utilizing the stem bark could mitigate the destructive harvesting practices that threaten the species' survival without compromising medicinal efficacy.
2. Solvent Polarity: The biological activity is heavily influenced by solvent polarity. The chloroform fractions, enriched with moderately lipophilic phenolics and flavonoids, demonstrated the highest bioactivity, suggesting that specific bioactive constituents are more effectively extracted or concentrated in this fraction.
3. Tissue Specificity: There are distinct differences in the accumulation of bioactive compounds between stem and root tissues, with the stem bark showing higher concentrations of phenolics and flavonoids, which correlates with its enhanced biological performance.

The authors conclude that these findings support the integration of stem bark into traditional therapeutic practices to promote species conservation and encourage future research into the isolation and structural characterization of the specific compounds responsible for these activities.