Impact of Storage Time on the Juice and Sugars Extracted from Chopped and Whole Stalk Sweet Pearl Millet and Sweet Sorghum Biomass

Since they have a high concentrations of fermentable sugars, sweet pearl millet and sweet sorghum are two interesting crops for bioethanol production. However, if the juice is not extracted from the biomass immediately after harvest, the biomass has to be transported and stored for further juice extraction. This delay could affect the amount of juice extracted and its sugar concentration. This paper presents the results of 3 years of experiments where different storage modes (chopped and whole stalks) and various storage time (0 to 14 days) were applied on two different crop species (sweet pearl millet and sweet sorghum). Storing sweet pearl millet as whole stalks for 2 weeks resulted in a water-soluble carbohydrate (WSC) concentration decrease of 52 %, while no significant decrease of the WSC concentration was observed for sweet sorghum. Whole stalks storage is much more efficient than storing the biomass chopped to avoid a rapid sugar loss. However, more juice can be extracted from stored chopped biomass than from stored whole stalks biomass. If the juice cannot be extracted quickly after the harvest, the biomass can be stored as whole stalks to avoid rapid sugar deterioration, especially for sweet sorghum.     

A Novel Wild-Type Saccharomyces cerevisiae Strain TSH1 in Scaling-Up of Solid-State Fermentation of Ethanol from Sweet Sorghum Stalks

The rising demand for bioethanol, the most common alternative to petroleum-derived fuel used worldwide, has encouraged a feedstock shift to non-food crops to reduce the competition for resources between food and energy production. Sweet sorghum has become one of the most promising non-food energy crops because of its high output and strong adaptive ability. However, the means by which sweet sorghum stalks can be cost-effectively utilized for ethanol fermentation in large-scale industrial production and commercialization remains unclear. In this study, we identified a novel Saccharomyces cerevisiae strain, TSH1, from the soil in which sweet sorghum stalks were stored. This strain exhibited excellent ethanol fermentative capacity and ability to withstand stressful solid-state fermentation conditions. Furthermore, we gradually scaled up from a 500-mL flask to a 127-m³ rotary-drum fermenter and eventually constructed a 550-m³ rotary-drum fermentation system to establish an efficient industrial fermentation platform based on TSH1. The batch fermentations were completed in less than 20 hours, with up to 96 tons of crushed sweet sorghum stalks in the 550-m³ fermenter reaching 88% of relative theoretical ethanol yield (RTEY). These results collectively demonstrate that ethanol solid-state fermentation technology can be a highly efficient and low-cost solution for utilizing sweet sorghum, providing a feasible and economical means of developing non-food bioethanol.     

A novel cost-effective technology to convert sucrose and homocelluloses in sweet sorghum stalks into ethanol

Background

Sweet sorghum is regarded as a very promising energy crop for ethanol production because it not only supplies grain and sugar, but also offers lignocellulosic resource. Cost-competitive ethanol production requires bioconversion of all carbohydrates in stalks including of both sucrose and lignocellulose hydrolyzed into fermentable sugars. However, it is still a main challenge to reduce ethanol production cost and improve feasibility of industrial application. An integration of the different operations within the whole process is a potential solution.

Results

An integrated process combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment was presented in this work. Soluble sugars in sweet sorghum stalks were firstly converted into ethanol by ASSF using crushed stalks directly. Then, the operation combining ethanol distillation and alkaline pretreatment was performed in one distillation-reactor simultaneously. The corresponding investigation indicated that the addition of alkali did not affect the ethanol recovery. The effect of three alkalis, NaOH, KOH and Ca(OH)₂ on pretreatment were investigated. The results indicated the delignification of lignocellulose by NaOH and KOH was more significant than that by Ca(OH)₂, and the highest removal of xylan was caused by NaOH. Moreover, an optimized alkali loading of 10% (w/w DM) NaOH was determined. Under this favorable pretreatment condition, enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was investigated. 92.0% of glucan and 53.3% of xylan conversion were obtained at enzyme loading of 10 FPU/g glucan. The fermentation of hydrolyzed slurry was performed using an engineered stain, Zymomonas mobilis TSH-01. A mass balance of the overall process was calculated, and 91.9 kg was achieved from one tonne of fresh sweet sorghum stalk.

Conclusions

A low energy-consumption integrated technology for ethanol production from sweet sorghum stalks was presented in this work. Energy consumption for raw materials preparation and pretreatment were reduced or avoided in our process. Based on this technology, the recalcitrance of lignocellulose was destructed via a cost-efficient process and all sugars in sweet sorghum stalks lignocellulose were hydrolysed into fermentable sugars. Bioconversion of fermentable sugars released from sweet sorghum bagasse into different products except ethanol, such as butanol, biogas, and chemicals was feasible to operate under low energy-consumption conditions.

     

Biorefinery of sweet sorghum stem

Sweet sorghum has been considered as a viable energy crop for alcohol fuel production. This review discloses a novel approach for the biorefining of sweet sorghum stem to produce multiple valuable products, such as ethanol, butanol and wood plastic composites. Sweet sorghum stem has a high concentration of soluble sugars in its juice, which can be fermented to produce ethanol by Saccharomyces cerevisiae. In order to obtain high ethanol yield and fermentation rates, concentrated juice with an initial total sugar concentration of 300gL(-1) was fermented. The maximum ethanol concentration after 54h reached 140gL(-1) with a yield of 0.49g ethanol per g consumed sugar, which is 97% of the theoretical value. Sweet sorghum bagasse, obtained from juice squeezing, was pretreated by acetic acid to hydrolyze 80-90% of the contained hemicelluloses. Using this hydrolysate as raw material (total sugar 55gL(-1)), 19.21gL(-1) total solvent (butanol 9.34g, ethanol 2.5g, and acetone 7.36g) was produced by Clostridium acetobutylicum. The residual bagasse after pretreatment was extruded with PLA in a twin-screw extruder to produce a final product having a PLA: fiber ratio of 2:1, a tensile strength of 49.5M and a flexible strength of 65MPa. This product has potential use for applications where truly biodegradable materials are required. This strategy for sustainability is crucial for the industrialization of biofuels from sweet sorghum.     

Evaluation and Modeling of Bioethanol Yield Efficiency from Sweet Sorghum Juice

One of the challenges with using sweet sorghum as an energy crop is that although fermentation of the juice to ethanol does not require enzymes, the juice can easily spoil. One strategy to avoid spoilage is to harvest the juice in the field, place it into a tanker for transport, and add the yeast immediately to initiate the fermentation process to begin during transport. Hence, it is also important to understand how the fermentation process is influenced by pH, temperature, and dissolved oxygen, since these parameters would not be “controlled” during transport. A full factorial design was applied to examine and optimize yield efficiency of ethanol production for the fermentation of sweet sorghum juice. Bioethanol yield efficiency was modeled using a linear equation. Under optimal pH (5.5), temperature (28 °C), and dissolved oxygen (0%) conditions, a maximum theoretical yield efficiency of 0.75 was achieved for bioethanol produced from M81E variety of sweet sorghum.     

Post-harvest Changes in Sweet Sorghum II: pH, Acidity, Protein, Starch, and Mannitol

This experiment was conducted to evaluate the effect of four harvesting methods on juice quality and storability in sweet sorghum. Three cultivars (Dale, Theis, and M81-E) were harvested at 90, 115, and 140 days after planting. Stalks were stripped of leaves and topped at the peduncle, then divided into four treatments (whole stalk, 20- or 40-cm billets, or chopped). The sorghum was stored outside at ambient temperature in a shade tent, and juice was extracted from samples removed at 0, 1, 2, and 4 days after harvest. Changes in juice Brix and sugars were reported in an earlier paper (Lingle, Tew, Rukavina, Boykin, Post-harvest changes in sweet sorghum I: Brix and sugars, BioEnergy Research 5:158–167, 2012). In this paper, we report changes in juice pH, titratable acidity (TA), and protein, starch, and mannitol concentrations. Juice pH dropped rapidly after harvest in chopped sorghum, but changed little during 4 days of storage in whole stalks or billets. Similarly, TA increased with storage time in chopped samples, but was unchanged in whole stalks and billets. Protein concentration was highly variable, and no pattern with treatment or storage time could be discerned. In whole stalks and billets, starch content slowly decreased during storage, while in chopped samples starch appeared to increase. This was most likely a result of an increase in dextran synthesized by microorganisms in those samples, which was also detected by the enzymatic starch assay. The concentration of mannitol increased with storage time in chopped samples, but not in whole stalks or billets. Within a harvest date, pH was highly correlated with total sugar, while TA and mannitol were highly negatively correlated with total sugar. The results confirm that whole stalks and billets were little changed over 4 days of storage, while chopped sorghum was badly deteriorated 1 day after harvest. Changes in pH, TA, or mannitol could be used to measure deterioration in sweet sorghum after harvest.     

先进固体发酵技术(ASSF)生产甜高粱乙醇

介绍了利用高产能源作物甜高粱生产燃料乙醇的先进固态发酵(ASSF)技术,从甜高粱茎秆保存、菌种、反应器,到固体发酵过程的数学模拟和工程放大进行了系统研究。筛选出高效产乙醇的菌种CGMCC1949,固体发酵时间低于30 h,乙醇收率高于92%;优选出贮存甜高粱茎秆的有效方法,通过抑菌处理,厌氧贮存200 d糖分损失小于5%;对固态发酵过程进行了数学模拟,设计并优化了固体发酵设备,成功进行了工程放大试验,并且基于ASPEN软件对该技术进行了技术经济评价,结果表明ASSF法生产甜高粱乙醇在技术、工程和经济上均具有充分的可行性和明显优势。     

Traditional method of making sorghum molasses

A time-honored but increasingly less common method of making a molasses from sweet sorghum,Sorghum bicolor, on a Tennessee farm is described. The thin, greenish juice extracted from the stalks is skillfully boiled and attended with specially designed equipment, resulting in a desirable sweet, golden product.     

Assessment of Sugarcane Billet Harvester on Recovery of Sweet Sorghum Biomass for Ethanol Production

Sweet sorghum (Sorghum bicolor L. Moench) is a promising bioenergy crop for the production of ethanol and bio-based products. Sugarcane billet harvesters can be used to harvest sweet sorghum. Multiple extractor fan speed settings of these harvesters allow for separating the extraneous matter in the feedstock, which has been associated with increased milling throughput and better juice quality at the processing facility. This removal is not completely selective, and some stalk material is also lost. These losses can be higher for sweet sorghum than sugarcane due its lower weight. This paper presents an assessment of how the speed of the primary extractor fan of a sugarcane billet combine used for harvesting sweet sorghum affects the biomass yield, biomass losses, and quality at delivery for the production of ethanol from extracted juice and fiber. Three primary extractor fan speeds (0, 800, and 1100 rpm) were evaluated. Higher fan speeds decreased fresh biomass yields by up to 28.3 Mg ha^?1. Juice quality was not significantly different among treatments. Ethanol yield calculated from sweet sorghum harvested at 0 rpm was 6075 L ha^?1. This value decreased by about half for material harvested at 1100 rpm due to the differences in biomass yield.     

Stalk Rot Diseases Impact Sweet Sorghum Biofuel Traits

Owing to its sugar-rich stalks and high biomass, sweet sorghum [Sorghum bicolor (L.) Moench] has potential as a source of biofuel feedstock for juice and lignocellulosic-based bioethanol production. However, stalk rot-mediated lodging is an important concern. The potential impacts of disease on sweet sorghum biofuel traits are currently unknown. The objectives of this study were to test the effects of Fusarium stalk rot and charcoal rot on sweet sorghum biofuel traits and to assess the combining ability of the parental genotypes for resistance to the two diseases. Nineteen genotypes including 7 parents and 12 hybrids were tested in the field in 2014 (Ashland, Kansas) and 2015 (Manhattan, Kansas) against Fusarium thapsinum (FT) and Macrophomina phaseolina (MP). Fourteen days after flowering, plants were inoculated with FT and MP. Plants were harvested at 35 days after inoculation and measured for disease severity using stalk lesion length. Grain weight, juice weight, Brix (°Bx), and dried bagasse weight were also determined. Total soluble sugars per plant (TSSP) were determined using juice weight and °Bx. On average, FT and MP resulted in reduced grain weight and dried bagasse weight by 17.4 and 17.6 %, respectively, across genotypes. Depending on the genotype, pathogens reduced juice weight, °Bx, and TSSP in the ranges of 11.3 to 25.9, 0.2 to 16.7, and 21.2 to 33.3 %, respectively. Parental line general and specific combining abilities were found to be statistically insignificant. This study revealed the adverse effects of stalk rot diseases on harvestable biofuel traits and the need to breed sweet sorghum for stalk rot resistance.     

Legacy effects of individual crops affect N2O emissions accounting within crop rotations

Uruguay is pursuing renewable energy production pathways using feedstocks from its agricultural sector to supply transportation fuels, among them ethanol produced from commercial technologies that use sweet and grain sorghum. However, the environmental performance of the fuel is not known. We investigate the life cycle environmental and cost performance of these two major agricultural crops used to produce ethanol that have begun commercial production and are poised to grow to meet national energy targets for replacing gasoline. Using both attributional and consequential life cycle assessment (LCA) frameworks for system boundaries to quantify the carbon intensity, and engineering cost analysis to estimate the unit production cost of ethanol from grain and sweet sorghum, we determined abatement costs. We found 1) an accounting error in estimating N₂O emissions for a specific crop in multiple crop rotations when using Intergovernmental Panel on Climate Change(IPCC) Tier 1 methods within an attributional LCA framework, due to N legacy effects; 2) choice of baseline and crop identity in multiple crop rotations evaluated within the consequential LCA framework both affect the global warming intensity (GWI) of ethanol; and 3) although abatement costs for ethanol from grain sorghum are positive and from sweet sorghum they are negative, both grain and sweet sorghum pathways have a high potential for reducing transport fuel GWI by more than 50% relative to gasoline, and are within the ranges targeted by the US renewable transportation fuel policies.     

Evaluation of Public Sweet Sorghum A-Lines for Use in Hybrid Production

A fundamental need for commercialization of sweet sorghum [Sorghum bicolor (L.) Moench] as a bioenergy crop is an adequate seed supply, which will require development of hybrid varieties using dwarf seed-parent lines. A set of six public sweet sorghum A-lines (Dwarf Kansas Sourless, KS9, N36, N38, N39, and N4692) were crossed with a set of six public sweet sorghum cultivars (Brawley, Kansas Collier, Dale, Sugar Drip, Waconia, and Wray). Grain, fiber, and sugar yields were determined, and conversion formulas were applied to estimate ethanol yields. Hybrids were grown in fields at Ithaca, NE, USA, in 1983–1984 fertilized with 112 kg ha^?1 N. In terms of yield components and overall ethanol yields, one A-line, N38, was inferior. Average total ethanol yields from hybrids made on the other A-lines were not significantly different, suggesting that any of those five A-lines could be useful seed-parents. With the exception of grain yield, cultivars used as pollen parents were among the highest-performing entries for all traits. For all traits directly contributing to total ethanol yield (grain yield, juice yield, % soluble solids, sugar yield, fiber yield), hybrids were also among the highest-performing entries. Results of this study demonstrate that hybrid sweet sorghum with performance criteria equivalent to existing sweet sorghum cultivars can be produced on the sweet sorghum seed-parent lines A-Dwarf Kansas Sourless, A-KS9, A-N36, A-N39, and A-N4692. Identification of specific seed-parent × pollen parent lines with characteristics best suited for particular growing regions and end-user needs will be critical for commercial hybrid development.     

Intermediate-Scale, Semicontinuous Solid-Phase Fermentation Process for Production of Fuel Ethanol from Sweet Sorghum

A novel, semicontinuous solid-phase fermentation system was used to produce fuel ethanol from sweet sorghum. The process was at an intermediate scale. In the process, dried and shredded sweet sorghum was rehydrated to 70% moisture, acidified to pH 2.0 to 3.0, and either pasteurized (12 h at 70 to 80°C) or not pasteurized before spray inoculation with a broth culture of Saccharomyces cerevisiae. Fermented pulp exited the semicontinuous fermentor after a retention time of 72 h and contained approximately 6% (vol/vol) ethanol. Ethanol yields from dry sweet sorghum were 176 to 179 liters/10³ kg (85% of theoretical). Production costs for a greatly scaled-up (×1,400) conceptual version of this system were projected by calculation to average $0.47/liter for 95% ethanol. The calculated energy balance (energy output/energy input ratio) was estimated to be 1.05 when pasteurization was included and 1.31 when pasteurization was omitted. In calculating the energy balances, the output energy of the protein feed byproduct and the input energy for growing the sweet sorghum were not considered. A design for the scaled-up plant (farm scale) is provided.     

Juice,sugar, and bagasse response of sweet sorghum (Sorghum bicolor (L.) Moench cv. M81E) to N fertilization and soil type

The objective of this research was to determine the optimum nitrogen fertilizer rate for producing sweet sorghum (a promising biofuel crop) juice, sugar, and bagasse on silt loam, sandy loam, and clay soils in Missouri. Seven nitrogen fertilization rates were applied, ranging from 0 to 134 kg N ha^?1. Regardless of the soil and year, the juice content of sweet sorghum stalk averaged 68.8% by weight. The juice yield ranged from 15.2 to 71.1 m³ ha^?1. Soil and N rate significantly impacted the juice yield (P < 0.0001). The pH and the density of the juice were not affected by the soil or N. The sugar content (Brix) of the juice varied between 10.7% and 18.9%. N fertilization improved the sugar content of the juice. A negative correlation existed between the sugar concentration and the juice yield. In general, the lowest sugar content was found in the clay soil and the impact of the N fertilization on juice sugar content was most pronounced in that soil. The juice sugar yield ranged between 2 and 9.9 Mg ha^?1, with significant differences found between years, N rates, and soils. N fertilization always increased the sugar yield in the clay soil, whereas in loam soil, a significant sugar response was recorded when the sweet sorghum was planted after corn. The average juice water content was 84% by weight. The dry bagasse yield fluctuated between 3.2 and 13.8 Mg ha^?1 with significant difference found with N rate, soil, and year. When sweet sorghum was grown after soybean or cotton, its N requirement was less than after a corn crop was grown the previous year. In general, a minimum of 67 kg N ha^?1 was required to optimize juice, sugar, and bagasse yield in sweet sorghum.     

Assessment of Stalk Properties to Predict Juice Yield in Sorghum

Sweet sorghum is an outstanding feedstock choice for bioethanol production, but the gap between theoretical and commercial ethanol yields must be reduced to improve economic viability. Extractable juice yield is a primary limiting factor for higher ethanol yield, but current phenotyping techniques to measure juice yield in sorghum can be laborious. Therefore, alternative approaches to measuring juice yield during selection are needed. The objectives of this study were to investigate the relationship between stalk-related traits and juice yield and to assess the ability to predict juice yield using agronomic traits and stalk properties across and within a diverse set of sorghum ideotypes (photoinsensitive, photosensitive, biomass, grain, and sweet types). Stalk weight, stalk volume, stalk diameter, and plant height had significantly strong associations with juice yield, which were consistent across different sorghum ideotypes. The direct and indirect effects of multiple predictive traits on juice yield varied greatly with the distinct sorghum subsets. However, equation modeling demonstrated that juice yield is satisfactorily predicted by jointly assessing stalk weight and stalk moisture. Moreover, alternative prediction models involving distinct combinations of agronomic and stalk-related traits had similarly good prediction accuracy. Altogether, this suggests that several prediction models can be used to accelerate phenotyping for juice yield, which will improve the selection process. Overall, the results indicate that increasing sorghum juice yield via indirect selection is possible, but the choice of prediction model depends on the ideotypes and resources available in a breeding program.     

Composition of sugar cane,energy cane,and sweet sorghum suitable for ethanol production at Louisiana sugar mills

A challenge facing the biofuel industry is to develop an economically viable and sustainable biorefinery. The existing potential biorefineries in Louisiana, raw sugar mills, operate only 3 months of the year. For year-round operation, they must adopt other feedstocks, besides sugar cane, as supplemental feedstocks. Energy cane and sweet sorghum have different harvest times, but can be processed for bio-ethanol using the same equipment. Juice of energy cane contains 9.8% fermentable sugars and that of sweet sorghum, 11.8%. Chemical composition of sugar cane bagasse was determined to be 42% cellulose, 25% hemicellulose, and 20% lignin, and that of energy cane was 43% cellulose, 24% hemicellulose, and 22% lignin. Sweet sorghum was 45% cellulose, 27% hemicellulose, and 21% lignin. Theoretical ethanol yields would be 3,609 kg per ha from sugar cane, 12,938 kg per ha from energy cane, and 5,804 kg per ha from sweet sorghum.     

Bioconversion of dilute-acid pretreated sorghum bagasse to ethanol by Neurospora crassa

Bioethanol production from sweet sorghum bagasse (SB), the lignocellulosic solid residue obtained after extraction of sugars from sorghum stalks, can further improve the energy yield of the crop. The aim of the present work was to evaluate a cost-efficient bioconversion of SB to ethanol at high solids loadings (16?% at pretreatment and 8?% at fermentation), low cellulase activities (1-7 FPU/g SB) and co-fermentation of hexoses and pentoses. The fungus Neurospora crassa DSM 1129 was used, which exhibits both depolymerase and co-fermentative ability, as well as mixed cultures with Saccharomyces cerevisiae 2541. A dilute-acid pretreatment (sulfuric acid 2?g/100?g SB; 210?°C; 10?min) was implemented, with high hemicellulose decomposition and low inhibitor formation. The bioconversion efficiency of N. crassa was superior to S. cerevisiae, while their mixed cultures had negative effect on ethanol production. Supplementing the in situ produced N. crassa cellulolytic system (1.0 FPU/g SB) with commercial cellulase and β-glucosidase mixture at low activity (6.0 FPU/g SB) increased ethanol production to 27.6?g/l or 84.7?% of theoretical yield (based on SB cellulose and hemicellulose sugar content). The combined dilute-acid pretreatment and bioconversion led to maximum cellulose and hemicellulose hydrolysis 73.3?% and 89.6?%, respectively.     

Ethanol production from sweet sorghum juice using very high gravity technology: Effects of carbon and nitrogen supplementations

Ethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP01 was investigated under very high gravity (VHG) fermentation and various carbon adjuncts and nitrogen sources. When sucrose was used as an adjunct, the sweet sorghum juice containing total sugar of 280 g l⁻¹, 3 g yeast extract l⁻¹ and 5 g peptone l⁻¹ gave the maximum ethanol production efficiency with concentration, productivity and yield of 120.68 ± 0.54 g l⁻¹, 2.01 ± 0.01 g l⁻¹ h⁻¹ and 0.51 ± 0.00 g g⁻¹, respectively. When sugarcane molasses was used as an adjunct, the juice under the same conditions gave the maximum ethanol concentration, productivity and yield with the values of 109.34 ± 0.78 g l⁻¹, 1.52 ± 0.01 g l⁻¹ h⁻¹ and 0.45 ± 0.01 g g⁻¹, respectively. In addition, ammonium sulphate was not suitable for use as a nitrogen supplement in the sweet sorghum juice for ethanol production since it caused the reduction in ethanol concentration and yield for approximately 14% when compared to those of the unsupplemented juices.     

Ethanol production by fermentation of sweet-stem sorghum juice using various yeast strains

Ethanol tolerance, osmotolerance and sugar conversion efficiency were used to screen yeasts for potential ethanol production from sweet-stem sorghum juice. Of the ten strains of Saccharomyces sp. that produced ethanol from the sorghum juice or from yeast extract/phosphate/sucrose (YEPS) media, the best sugar conversion efficiencies were greater than 85% for the strains Vin7, SB9, N96 and GSL. Vin7 and SB9 had higher sugar conversion efficiencies for sweet-stem sorghum juice, while strains N96 and GSL gave higher conversions in YEPS.The authors are with the Food and Fermentation Laboratory, Department of Biochemistry, University of Zimbabwe, M.P.167. Mount Pleasant, Harare, Zimbabwe     

Study of a single and mixed culture for the direct bio-conversion of sorghum carbohydrates to ethanol

Fusaium oxysporum F3 alone or in mixed culture with Saccharomyces cerevisiae 2541 fermented soluble and insoluble carbohydrates of sweet sorghum stalk directly to ethanol. Both microorganisms were first grown aerobically and fermented sorghum stalk to ethanol thereafter. During fermentation, insoluble carbohydrates were hydrolysed to soluble sugars by the celluloytic system of F. oxysporum. Ethanol yields as high as 24.4 and 33.5 g/100 g dry stalks were obtained by F. oxysporum and the mixed culture respectively, representing a theoretical yield enhancement of 11.6% and 53.6% respectively. The corresponding ethanol concentrations in the fermentation medium were 4.6% and 6.4% (w/v). These results clearly demonstrated that a large portion of insoluble carbohydrate from sorghum was converted by simultaneous saccharification and fermentation to ethanol, making the process promising for bioethanol production.