Effect of nutrient addition on preinoculum growth of S. cerevisiae for application in SSF processes

The expansion of established cereal-based plants by integrating second generation ethanol production into their current operations might be the best first step to successful commercialization of cellulosic ethanol. Joining first and second generation facilities could allow costs reduction for new technology implementation. The media supplementation components have a very strong impact on the economy of the industrial fermentation process. It is necessary to optimize the nutrient sources to fulfill the nutritional requirements for microorganism growth and fermentation. In this context, the grain mash obtained after liquefaction in first generation ethanol production processes have been employed as nutrient in the inoculum growth. Inocula obtained solely from grain mash have been compared to those obtained from media supplemented with other nutrients.The studied chemical compounds have been selected from those commonly employed in fermentation of lignocellulosic hydrolysates. These include urea, (NH4)2HPO4 plus (NH4)2SO4, NH4OH plus H3PO4, and KH2PO4 plus (NH4)2SO4.All inocula have been tested in simultaneous saccharification and fermentation (SSF) at high substrate loading (16.5% w/w) from wheat straw pretreated with acid steam explosion. It is remarkable that inoculum obtained exclusively with the grain mash has been robust enough to produce high ethanol concentration in the SSF without addition of extra nutrients.Furthermore, it is essential to optimize the whole bioethanol production process developing appropriate fermentation conditions and parameters. Thus, temperatures ranging from 32 to 37 °C and pH from 4.5 to 5.5 have also been studied for optimizing the preinoculum growth as well as ethanol production in the SSF.

► We show an option for implementing first and second generation bioethanol production.
► Grain mash is combined with wheat straw hydrolysate for inoculum growth.
► Medium with higher prehydrolysate proportion result in a more tolerant population.
► Cells grown with urea and (NH4)2HPO4:(NH4)2SO4 perform well in SSF without nutrients.