Optimized ultrasound-assisted extraction for phenolic and antioxidant analysis in purple senggani (Melastoma malabathricum) flowers: Influence of developmental stages

Abstract

The purple-flowered senggani (Melastoma malabathricum) is known to contain significant phenolic compounds with strong antioxidant potential, making it a valuable candidate for natural antioxidant sources. To enhance the extraction of these bioactive compounds, ultrasound-assisted extraction (UAE) was selected due to its efficiency in disrupting cell walls, accelerating compound release, and offering an environmentally friendly alternative to conventional methods. This study aimed to optimize the UAE method to analyze phenolic compounds across different flower developmental stages, which affect total phenolic content (TPC) and total antioxidant capacity (TAC). Key variables such as temperature, pulse-duty cycle, solvent composition, and solvent-to-sample ratio were optimized using response surface methodology. The optimal UAE conditions were determined as 70 °C, a pulse-duty cycle of 0.6 s⁻¹, 40 % methanol in water, and a sample-to-solvent ratio of 1:10, with a 15-min extraction time. Method validation demonstrated high precision, with coefficients of variation for repeatability (n = 9) at 0.44 % for TPC and 0.37 % for TAC and intermediate precision (n = 3 × 3) at 1.54 % and 2.61 %, respectively. The method achieved 100 % accuracy over two extraction cycles. Among the developmental stages, the bud stage (S₁) exhibited the highest TPC (445.79 ± 4.63 mg GAE g⁻¹) and TAC (53.02 ± 0.43 %). Five phenolic compounds were analyzed, including four identified compounds—rutin, quercetin 3-glucoside, trifolin, and astragalin—and one unidentified flavonoid compound. This optimized UAE method supports detailed phenolic profiling of senggani flowers, offering insights into their potential for natural antioxidant applications.