Optimization of Antioxidant Extraction from Red Ginger Rhizomes (Zingiber officinale var. Rubrum) Using Response Surface Methodology

Abstract

The body generates endogenous antioxidants to neutralize free radicals however, when these are insufficient, antioxidants from natural sources become essential. Among these sources, the rhizome of red ginger (Zingiber officinale var. rubrum) is well known for its abundance of phenolic substances and notable antioxidant activity. This makes it a promising material for the enhancement of functional ingredients and therapeutic formulations. However, the efficiency of extraction largely depends on the experimental conditions. This study aimed to identify the optimal condition for the extraction of antioxidants from red ginger utilizing the decoction method. To achieve this, Response Surface Methodology (RSM) with a Central Composite Design (CCD) was used to test how the extraction temperature, extraction time, and sample-to-solvent ratio collectively impact the antioxidant capacity and the precision of the predictive model. The One Factor at A Time (OFAT) approach was initially used to decide the midpoint values of the parameter used in the RSM design. The antioxidant capacity was assessed using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, tested utilizing a UV-visible spectrophotometer. Based on the RSM analysis, the optimal condition were established at 90°C for 50 minutes by a sample-to-solvent ratio of 1:25 g/mL. The maximum antioxidant capacity achieved was 3.7811 mg AAE/g FW, that was closely aligned with the RSM model’s predicted value of 3.87587 mg AAE/g FW. The analysis of variance (ANOVA) indicated a p-value below 0.05, showing that extraction temperature, extraction time, and the sample-to-solvent ratio had a substantial impact on antioxidant capacity.