Optimization of starch extraction from Plectranthus edulis tubers using response surface methodology and evaluation of physicochemical and functional properties

Plectranthus edulis is an indigenous Ethiopian tuber crop with potential as a starch source, although information on the optimization of its starch extraction process remains limited. This study aimed to optimize starch extraction from P. edulis tubers using Response Surface Methodology (RSM) based on a Box–Behnken Design (BBD). The effects of extraction temperature, pH, and extraction time on starch yield were evaluated using sodium metabisulphite as the extraction medium. A quadratic model adequately described the relationship between the process variables and starch yield and was used to determine the optimum extraction conditions. The optimum extraction conditions were 55.17 °C, pH 5.42, and 52.58 min, resulting in a starch yield of 97.10%. The extracted starch was characterized for its physicochemical and functional properties. The starch contained 9.8 ± 0.2% moisture, 0.12 ± 0.03% ash, 0.52 ± 0.05% protein, 0.15 ± 0.01% lipid, and 32.4 ± 0.24% amylose. In addition, the starch exhibited a bulk density of 0.58 ± 0.21 g/mL, tapped density of 0.82 ± 0.01 g/mL, Carr’s index of 18.2 ± 1.40%, and a Hausner ratio of 1.07 ± 0.11, indicating favorable flow characteristics. The water absorption capacity and swelling power were 9.2 ± 0.49 g/g and 3.5 ± 0.28 g/g, respectively. The findings demonstrate that Response Surface Methodology is an effective tool for optimizing starch extraction from P. edulis tubers. The extracted starch exhibited acceptable physicochemical and functional properties and contributes to the growing body of knowledge on this underutilized crop. Further studies involving advanced structural characterization and application-specific evaluations are recommended.