Taguchi Method. The Taguchi method was used to determine the best set of extraction conditions while minimizing the required number of experiments. A Taguchi DOE workflow is shown in Supplemental Figure and consists of: the selection of control factors, determination of levels, selection of orthogonal array, collection of experimental data, data analysis, signal-tonoise (S/N) calculations, analysis of variation (ANOVA), and the evaluation of optimum performance. Control factors refer to specific study variables, and levels refer to the defined setting of each control factor. An L'9 orthogonal array was used to investigate four metabolite extraction factors at three levels each, as shown in Supplemental Table .