A novel aeration strategy in repeated-batch fermentation for efficient ethanol production from sweet sorghum juice

To improve the efficiency of ethanol production in a batch fermentation from sweet sorghum juice under a very high gravity(VHG) condition(～ 290 g/L of total sugar) by Saccharomyces cerevisiae NP01, repeatedbatch fermentation under an aerated condition(2.5 vvm for the first 4 h during every cycle) was done in a5-L fermenter. The average ethanol concentration(P), productivity(Qp) and yield(Yp/s) for five successive cycles were 112.31 g/L, 1.55 g/L·h~(-1) and 0.44, respectively with 80.97% sugar consumption. To complete sugar consumption, the total sugar of the juice was reduced to a high gravity(HG) level(～240 g/L). The results showed that yeast extract was not necessary for ethanol production, and aeration during every other cycle i.e., alternating cycles, was sufficient to promote both yeast growth and ethanol production.The average P, Qpand Yp/svalues for eight successive cycles with aeration during alternating cycles were97.58 g/L, 1.98 g/Láh and 0.41, respectively with 91.21% sugar consumption. The total fatty acids in the yeast cells under the aerated condition were ～ 50% higher than without aeration, irrespective the initial sugar concentration, whereas the ergosterol contents under aeration condition were ～ 29% to 49% higher than those without aeration.