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Cereal Chem. 84(2):130-136The goal of this research is to understand the key factors affecting ethanol production from grain sorghum. Seventy genotypes and elite hybrids with a range of chemical compositions and physical properties selected from ≈1,200 sorghum lines were evaluated for ethanol production and were used to study the relationships of composition, grain structure, and physical features that affect ethanol yield and fermentation efficiency. Variations of 22% in ethanol yield and 9% in fermentation efficiency were observed among the 70 sorghum samples. Genotypes with high and low conversion efficiencies were associated with attributes that may be manipulated to improve fermentation efficiency. Major characteristics of the elite sorghum genotypes for ethanol production by the drygrind method include high starch content, rapid liquefaction, low viscosity during liquefaction, high fermentation speed, and high fermentation efficiency. Major factors adversely affecting the bioconversion process are tannin content, low protein digestibility, high mash viscosity, and an elevated concentration of amylose-lipid complex in the mash.

Cereal Chem. 83(5):569-575The effects of amylose, protein, and fiber contents on ethanol yields were evaluated using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as media made from different cereal sources including corn, sorghum, and wheat with different amylose contents. Second-order response-surface regression models were used to study the effects and interactions of amylose, protein, and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P < 0.001) effect on ethanol conversion efficiency. No significant effect of protein content on ethanol production was observed. Fiber did not show a significant effect on ethanol fermentation either. Conversion efficiencies increased as the amylose content decreased, especially when the amylose content was >35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic model does. Fermentation tests on mashes made from corn, sorghum, and wheat samples with different amylose contents confirmed the adverse effect of amylose content on fermentation efficiency. Hightemperature cooking with agitation significantly increased the conversion efficiencies on mashes made from high-amylose (35-70%) ground corn and starches. A cooking temperature of ≥160°C was needed on highamylose corn and starches to obtain a conversion efficiency equal to that of normal corn and starch.

Sorghum is a major cereal crop in the USA. However, sorghum has been underutilized as a renewable feedstock for bioenergy. The goal of this research was to improve the bioconversion efficiency for biofuels and biobased products from processed sorghum. The main focus was to understand the relationship among "genetics-structure-function-conversion" and the key factors impacting ethanol production, as well as to develop an energy life cycle analysis model (ELCAM) to quantify and prioritize the saving potential from factors identified in this research. Genetic lines with extremely high and low ethanol fermentation efficiency and some specific attributes that may be manipulated to improve the bioconversion rate of sorghum were identified. In general, ethanol yield increased as starch content increased. However, no linear relationship between starch content and fermentation efficiency was found. Key factors affecting the ethanol fermentation efficiency of sorghum include protein digestibility, level of extractable proteins, protein and starch interaction, mash viscosity, amount of phenolic compounds, ratio of amylose to amylopectin, and formation of amylose-lipid complexes in the mash. A platform ELCAM with a base case showed a positive net energy value (NEV) = 25,500 Btu/gal EtOH. ELCAM cases were used to identify factors that most impact sorghum use. For example, a yield increase of 40 bu/ac resulted in NEV increasing from 7 million to 12 million Btu/ac. An 8% increase in starch provided an incremental 1.2 million Btu/ac.

Increasing demand for renewable fuel sources has stimulated the need for alternative biomass crops. A study was conducted to determine grain, stover, total biomass, and estimated ethanol yields of annual and perennial crops at two locations in Kansas in 2007 and 2008. Th is study included corn (Zea mays L.) grown continuously and rotated with soybean [Glycine max (L.) Merr.]; fi ve sorghum cultivars, brown midrib (bmr), photoperiod sensitive, sweet, and two dual-purpose forage varieties; and three perennial warm-season grasses, switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and Miscanthus (Miscanthus × giganteus). Corn and sorghum plants were harvested for grain and biomass and sweet sorghum stalks were pressed to extract juices. Perennial grasses were harvested for biomass. Highest grain yields were achieved with corn across both years and locations with yields averaging 10.1 Mg ha -1 . Total biomass yields were greatest for sweet sorghum (32.6 and 28.2 Mg ha -1 in 2007 and 2008, respectively) and photoperiod-sensitive sorghum (26.8 Mg ha -1 in 2007). Sweet sorghum extracted fermentable carbohydrate yields averaged 4.8 Mg ha -1 . Perennial grass biomass yields ranged from 7.7 to 12.8 Mg ha -1 in 2008, the second year aft er establishment. Highest average estimated ethanol yields were achieved with sweet sorghum (9920 L ha -1 ). Th ese results indicate that the highest total biomass and estimated ethanol yields for renewable fuel production can be achieved from sweet sorghum and that perennial grasses were as productive as annual crops at producing biomass in the fi rst 2 yr aft er planting.