DOE based optimisation of extraction process for fruits of Kigelia africana

Kigelia africana fruit has rich phenolic bioactives; verbascoside (VBS), caffeic acid (CA), coumaric acid (COA), and ferulic acid (FA) which underlie its antimicrobial and antioxidant properties. A systematic 22 full-factorial design approach was applied, varying ethanol concentration (50%, 100%) and extraction time (18 h, 36 h). Quantitative analysis employed validated HPTLC methods, which were linear, precise, and accurate. ANOVA of the 2FI model confirmed that both solvent level and time (and their interaction) significantly affected yields (p < 0.05). Extended extraction (36 h) markedly increased VBS (130–150 µg/mL) concentration, indicating time-driven release. CA (200–280 µg/mL) and FA (150–210 µg/mL) recoveries were maximised with 100% ethanol and longer time, reflecting strong ethanol × time interactions. In contrast, COA yield (28.1–32.8 µg/mL) was governed mainly by the combined high-ethanol, long-time condition. Notably, significant interaction terms show that the effect of ethanol depends on extraction time (and vice versa), illustrating the advantage of factorial design.