Formulation and Antistaphylococcal Activity of Alpinia galanga (L.) Extract Lotion

Abstract

Background and Objectives: The global increase in antimicrobial resistance among clinical strains of Staphylococcus aureus has severely compromised the efficacy of conventional topical antibiotic therapies. Staphylococcus aureus remains a primary bacterial pathogen responsible for a wide spectrum of cutaneous infections, including impetigo, folliculitis, furuncles, and primary abscesses. Moreover, research attention has shifted toward bio-prospective medicinal plants to develop safe, effective, and natural topical cosmeceuticals. Alpinia galanga (L.) Sw. (Zingiberaceae), commonly known as galangal or Siamese ginger, is a traditional Asian medicinal plant whose rhizomes possess potent antibacterial, anti-inflammatory, and antioxidant properties driven by diverse secondary metabolites. Despite known antimicrobial activity of A. galanga extracts, limited scientific research exists regarding its systematic incorporation into stable topical lotion emulsions and the subsequent impact of extract loading on delivery vehicle stability and bioactive release. Therefore, this study aimed to formulate an Alpinia galanga rhizome extract-based oil-in-water (o/w) topical lotion at varying concentrations (25%, 50%, and 75% w/w), systematically evaluate its physicochemical quality control parameters (pH, viscosity, spreadability, organoleptic features, and emulsion type), and determine its in-vitro antistaphylococcal efficacy to identify the optimal therapeutic concentration threshold.
Methodology: Processed A. galanga rhizomes were shade-dried for four days and subjected to cold maceration using 95% ethanol. The liquid extract was concentrated under reduced pressure using a rotary evaporator, and the percentage crude yield was calculated relative to the initial dry biomass weight. The crude extract underwent baseline physicochemical characterization (pH, color, odor, taste, appearance, and solubility across solvents) and qualitative phytochemical screening for flavonoids, phenols, tannins, alkaloids, glycosides, saponins, and proteins using standard colorimetric protocols. An oil-in-water (o/w) lotion base was prepared by heating the oil phase (stearic acid, coconut oil) and aqueous phase (distilled water, xanthan gum, triethanolamine) independently to 75 °C, followed by continuous mechanical agitation to generate an in-situ stearate soap network reinforced by an anionic polymer. Additional excipients (glycerin, titanium dioxide, preservatives, essential oil fragrances) were incorporated upon cooling. Crude A. galanga extract was incorporated at 25%, 50%, and 75% (w/w) formulations. It were then evaluated for organoleptic characteristics, emulsion type via the water dilution test, pH using a 10% aqueous dispersion, viscosity using a rotary viscometer (25 rpm), and spreadability via the parallel plate method applying a 500 g weight. In-vitro antibacterial activity against Staphylococcus aureus was evaluated using the agar well diffusion method, comparing the test lotions against a positive control (2% fusidic acid cream) and a negative control (unadulterated lotion base) after 19 hours of incubation at 37 °C. Zones of inhibition were measured in millimeters using a digital Vernier caliper, and mean differences were evaluated statistically using Tukey's post-hoc test.
Main Results: Maceration of 700.0 g of dried rhizome yielded 21.5 g of crude ethanolic extract, corresponding to a percentage yield of 3.07%. The extract was a dark brown, viscous semi-liquid with an aromatic odor, bitter taste, and near-neutral pH of 6.57. It was soluble in water, sparingly soluble in ethanol, and insoluble in hexane. Phytochemical screening confirmed the presence of flavonoids, alkaloids, phenols, glycosides, and saponins, while testing negative for tannins and proteins. All formulated lotions maintained a uniform citrus-mint aroma, complete physical homogeneity, and an oil-in-water emulsion structure. Increasing extract concentration caused the lotion pH to drop from 6.73 (25% AG) to 5.91 (50% AG) and 5.68 (75% AG), remaining within safe skin physiological limits. Viscosity exhibited a non-linear decline from 42.80 mPa·s at 25% loading to 36.20 mPa·s at 50% loading, followed by a severe matrix collapse to 9.88 mPa·s at 75% loading. Spreadability demonstrated a parabolic trend, measuring 28.36 mm (25% AG), 33.36 mm (50% AG), and 28.33 mm (75% AG). In the antibacterial assay, the 25% AG lotion demonstrated potent inhibition against S. aureus with a mean zone of inhibition of 22.40 mm, which was statistically equivalent to 2% fusidic acid (21.70 mm, p > 0.05). On the other hand, the 50% AG lotion (13.30 mm) and 75% AG lotion (11.70 mm) showed significantly reduced activity, performing statistically no better than the untreated lotion base (12.80 mm).
Conclusions: The 25% A. galanga lotion is the optimal, stable, and therapeutically effective formulation for topical application against S. aureus infections. Exceeding a 25% extract concentration causes chemical overload from acidic phytoconstituents and electrolytes, which neutralizes the electrical charges of the xanthan gum polymer and breaks down the stearate soap matrix. This physical vehicle collapse leads to micellar entrapment, physically locking bioactive compounds within the formulation and preventing their diffusion into target tissues. Future research should explore non-ionic gel networks, advanced extraction methods (such as microwave-assisted extraction), and quantitative chromatographic profiling.