Response surface methodology for optimization of antioxidative activity: Elephant ginger (Zingiber officinale Roscoe)

Context: Elephant ginger (Zingiber officinale Roscoe) is valued for its antioxidative properties, which help combat oxidative stress-related diseases. The extraction method has a significant influence on the antioxidant yield and efficacy. Aims: To optimize the extraction process of Z. officinale rhizome using maceration and pressing techniques and to identify the flavonoid compounds in the optimal extract. Methods: A Box-Behnken design within the Response Surface Methodology (RSM) framework was used to evaluate three variables: extraction time (10–40 min), sample-to-solvent ratio (1:3–1:10), and ethanol concentration (70–96%). Antioxidant activities (CUPRAC, FRAP, DPPH), total phenolic content (TPC), and total flavonoid content (TFC) were measured. High-performance liquid chromatography (HPLC) was employed for the identification of flavonoids. Results: The optimized extraction conditions—40 minutes, a crude drug-to-solvent ratio of 1:3, and 96% ethanol—yielded 10.133 ± 0.382 mg gallic acid equivalent (GAE)/g for TPC and 4.922 ± 0.199 mg quercetin equivalent (QE)/g for TFC. Antioxidant activities were recorded as 19.107 ± 0.498 mg AEAC/g (DPPH), 20.793 ± 0.960 mg AEAC/g (CUPRAC), and 27.281 ± 0.589 mg AEAC/g (FRAP). A strong correlation was observed between phenolic and flavonoid content and antioxidative activity, with rutin identified as the predominant flavonoid (0.979 ± 0.087 mg/g). Conclusions: The study established optimal extraction conditions for maximizing the antioxidant potential of Z. officinale. The presence of phenolic and flavonoid compounds, particularly rutin, contributed significantly to the antioxidant activity. These findings offer a practical basis for standardizing ginger extracts in food, nutraceutical, and pharmaceutical industries.