2.6. Orthogonal Experiment Design of Nutrient Supplementation
The orthogonal design L9 (34) was used to investigate the influence of nutrient supplement dose of
Zn2+ (A), Mg2+ (B), Mn2+ (C) and yeast extract (D) on ethanol fermentation. Each supplement or factor
was set at three levels (A: 0.01, 0.03 and 0.05 g∙L−1; B: 0.05, 0.1 and 0.15 g·L−1; C: 0.01, 0.025 and
0.04 g·L−1; D: 3, 6 and 9 g·L−1). The L9 (34) orthogonal design is shown in Table 2. The nutrients at the
different doses (Table 2) were supplemented into the EP medium. Nine experiments of the ethanol
fermentation were carried out in duplicate as described in Section 2.5. The ethanol concentration and
ethanol productivity were used as response values to analyse the order of nutrient and the optimum
condition. Analysis of variance (ANOVA) was used as the tool of analysis.