Kinetic modeling of simultaneous saccharification and fermentation of corn starch for ethanol production.

Abstract

Fuel ethanol production, using a simultaneous saccharification and fermentation process (SSF) of native starch from corn flour, has been performed using Saccharomyces cerevisiae and a granular starch hydrolyzing enzyme. The quantitative effects of mash concentration, enzyme dose and pH were investigated with the use of a Box-Wilson central composite design protocol. Proceeding from results obtained in optimal fermentation conditions, a kinetics model relating the utilization rates of starch and glucose as well as the production rates of ethanol and biomass was tested. Moreover, scanning electron microscopy (SEM) was applied to investigate corn starch granule surface after the SFF process. A maximum ethanol concentration of 110.36 g/l was obtained for native corn starch using a mash concentration of 25%, which resulted in ethanol yield of 85.71%. The optimal conditions for the above yield were found with an enzyme dose of 2.05 ml/kg and pH of 5.0. These results indicate that by using a central composite design, it is possible to determine optimal values of the fermentation parameters for maximum ethanol production. The investigated kinetics model can be used to describe SSF process conducted with granular starch hydrolyzing enzymes. The SEM micrographs reveal randomly distributed holes on the surface of granules.

Effect of Pre-hydrolysis on Simultaneous Saccharification and Fermentation of Native Rye Starch

“…Saccharomyces yeast used for ethanol production schematically uses the available fermentable sugars. Having consumed glucose, they utilize maltose, followed by maltotriose (Białas et al 2014). The changes in the sugar profile have not been exactly described in the literature.…”

Evaluation of a recombinant insect-derived amylase performance in simultaneous saccharification and fermentation process with industrial yeasts

“…According to the primary assumptions made for the kinetic studies, this model assumes action of only one “amylolytic activity,” comprising synergetic action of alpha-amylase and glucoamylase, generating glucose (dp1) as the final product. Such an approach has been earlier applied in similar studies (Białas et al 2014 ; Davis 2008 ; Kroumov et al 2006 ). Equation 1 comprises two terms representing respectively the first and the second phase of the starch decomposition reaction (as explained in the third assumption of the model description in the “ Materials and methods ” section).…”

“…As it was previously demonstrated, a clear division of the starch enzymatic hydrolysis into the two phases (of low and high product concentration) is reasonable due to susceptibility of the catalysts to feedback inhibition by the product. According to Białas et al ( 2014 ), amylolytic activities contained in the Stargen preparation are greatly inhibited by glucose, at negligible inhibition by starch, even though the cultivations were conducted according to the SSF strategy. Similar conclusions were drawn by Polakovic and Bryjak ( 2004 ), as well as by Kroumov et al ( 2006 ).…”

“…Raw starch hydrolyzing enzymes (RSHE) constitute an excellent solution to this limitation. Application of RSHE, instead of traditional enzymes, allow to exclude the costly high-temperature mashing step from the bioethanol production pipeline, which in the further perspective may lead to more sustainable processing (Białas et al 2014 ). Conventional enzymatic preparations used in traditional bioethanol production processes contain liquefying alpha-amylase and saccharifying glucoamylase, operating at 90 to 110 °C and 60 to 70 °C, respectively (Sharma et al 2007 ).…”

“…According to the results by Robertson et al ( 2006 ), the reduction in the overall energy input, conveyed by the usage of RSHE in ethanol production, equals to 10–20 %. A direct consequence of RSH enzyme application in the bioethanol production pipeline is running the process according to a simultaneous saccharification and fermentation (SSF) strategy (Białas et al 2014 ). Simultaneous provision of amylolytic agent (RSHE - acting on nonpretreated substrate) and yeast cells (consuming saccharides released from starch granules) offers several advantages over the traditional two-step bioethanol production technologies (separate saccharification and fermentation).…”