Abstract: Optimization of four parameters, i.e., zinc (Zn2+), magnesium (Mg2+),
manganese (Mn2+) and yeast extract for bioethanol production from sweet sorghum juice
by Saccharomyces cerevisiae NP 01 under very high gravity (VHG, 270 g·L−1 of total
sugar) conditions was performed using an L9 (34) orthogonal array design. The
fermentation was carried out at 30 °C in 500-mL air-locked Erlenmeyer flasks at the
agitation rate of 100 rpm and the initial yeast cell concentration in the juice was
approximately 5 × 107 cells·mL−1. The results showed that the order of influence was yeast
extract > Mn2+ > Zn2+ > Mg2+ and the optimum nutrient concentrations for the ethanol
fermentation were Zn2+, 0.01; Mg2+, 0.05; Mn2+, 0.04; and yeast extract, 9 g·L−1. The
verification experiments under the optimum condition clearly indicated that the metals and
nitrogen supplementation improved ethanol production efficiency under the VHG
fermentation conditions. The ethanol concentration (P), yield (Yp/s) and productivity (Qp)
were 120.58 ± 0.26 g·L−1, 0.49 ± 0.01 and 2.51 ± 0.01 g·L−1·h−1, respectively, while in the