Dry-grind processing using amylase corn and superior yeast to reduce the exogenous enzyme requirements in bioethanol production

Abstract

BackgroundConventional corn dry-grind ethanol production process requires exogenous alpha and glucoamylases enzymes to breakdown starch into glucose, which is fermented to ethanol by yeast. This study evaluates the potential use of new genetically engineered corn and yeast, which can eliminate or minimize the use of these external enzymes, improve the economics and process efficiencies, and simplify the process. An approach of in situ ethanol removal during fermentation was also investigated for its potential to improve the efficiency of high-solid fermentation, which can significantly reduce the downstream ethanol and co-product recovery cost.ResultsThe fermentation of amylase corn (producing endogenous α-amylase) using conventional yeast and no addition of exogenous α-amylase resulted in ethanol concentration of 4.1 % higher compared to control treatment (conventional corn using exogenous α-amylase). Conventional corn processed with exogenous α-amylase and superior yeast (producing glucoamylase or GA) with no exogenous glucoamylase addition resulted in ethanol concentration similar to control treatment (conventional yeast with exogenous glucoamylase addition). Combination of amylase corn and superior yeast required only 25 % of recommended glucoamylase dose to complete fermentation and achieve ethanol concentration and yield similar to control treatment (conventional corn with exogenous α-amylase, conventional yeast with exogenous glucoamylase). Use of superior yeast with 50 % GA addition resulted in similar increases in yield for conventional or amylase corn of approximately 7 % compared to that of control treatment. Combination of amylase corn, superior yeast, and in situ ethanol removal resulted in a process that allowed complete fermentation of 40 % slurry solids with only 50 % of exogenous GA enzyme requirements and 64.6 % higher ethanol yield compared to that of conventional process.ConclusionsUse of amylase corn and superior yeast in the dry-grind processing industry can reduce the total external enzyme usage by more than 80 %, and combining their use with in situ removal of ethanol during fermentation allows efficient high-solid fermentation.

Saccharomyces cerevisiae strains for second-generation ethanol production: from academic exploration to industrial implementation

“…the full integration of pretreatment, hydrolysis and fermentation towards ethanol in a single microbial process step, remains a ‘holy grail’ in lignocellulosic ethanol production. Engineered starch-hydrolysing S. cerevisiae strains are already applied in first-generation processes (Kumar and Singh 2016 ). The first important steps towards efficient cellulose and xylan hydrolysis by S. cerevisiae have been made by functional expression of heterologous polysaccharide hydrolases (Olson et al.…”

Germ soak water as nutrient source to improve fermentation of corn grits from modified corn dry grind process

“…Theoretical yields were estimated based on the starch content, assuming complete starch conversion and 100% fermentation efficiency. Actual ethanol yields were determined by calculating liquid volume in final slurry at end of fermentation (Kumar and Singh 2016 ). Final slurry was weighed and a sample of the slurry was dried in hot air oven at 105 °C till constant weight was achieved (~24 h) to estimate the solid percent in the slurry.…”

Effects of Different Mill Types on Ethanol Production Using Uncooked Dry‐Grind Fermentation and Characteristics of Residual Starch in Distiller's Dried Grains (DDG)

“…The results suggested that damaged starch content had more impact on the starch hydrolysis and ethanol production than did the particle size of dry-grind corn. A regular dent corn was reported to provide 2.9 gal/bu ethanol yield via a conventional dry-grind corn process (Lemuz et al 2009;Kumar and Singh 2016). Therefore, sample A provided comparable ethanol yield (2.93-2.98 gal/bu) to the regular dent corn, whereas sample D gave higher ethanol yield (3.00-3.02 gal/bu) than the regular one.…”

“…Mill types used for dry-grinding affected the ethanol production for all samples, especially after 24 and 48 h fermentation time. A regular dent corn was reported to provide 2.9 gal/bu ethanol yield via a conventional dry-grind corn process (Lemuz et al 2009;Kumar and Singh 2016). All hammer-milled samples showed the lowest ethanol production at 72 and 96 h. The differences in ethanol yield between the cyclone-and hammer-milled samples ranged from 0.1 to 0.4% at 72 h. After 96 h, the ethanol yield differences between the cyclone-and hammermilled samples ranged from 0.0 to 0.2%.…”