Genotypic variations in non-structural carbohydrate and cell-wall components of the stem in rice, sorghum, and sugar vane

We evaluated genetic variations in the non-structural carbohydrate (NSC) and the cell-wall components of stem in rice, sorghum, and sugar cane to assess the potential suitability of these gramineous crops for bioethanol production. For NSC, the maximum soluble sugar concentration was highest in sugar cane, followed by sorghum with sucrose. The major NSC in rice was starch, but there were wide variations in the starch to soluble sugar ratios among the cultivars. The total concentration of cell-wall components was negatively correlated with the NSC concentration, indicating competition for carbon sources. Among the cell-wall components, lignin was relatively stable within each group. The major sugar species composing hemicellulose was xylose in all crop groups, but there were differences in composition, with a higher fraction of arabinose and glucose in rice as compared to the other crops. In rice, there was less lignin than in sorghum or sugar cane; this might be advantageous for the efficient saccharification of cellulose.     

Ethanol production from lignocellulosic biomass of energy cane

Ethanol produced from lignocellulosic biomass is a renewable alternative to diminishing petroleum based liquid fuels. The release of many new sugarcane varieties by the United States Department of Agriculture to be used as energy crops is a promising feedstock alternative. Energy cane produces large amounts of biomass that can be easily transported, and production does not compete with food supply and prices because energy cane can be grown on marginal land instead of land for food crops. The purpose of this study was to evaluate energy cane for lignocellulosic ethanol production. Energy cane variety L 79-1002 was pretreated with weak sulfuric acid to remove lignin. In this study, 1.4 M sulfuric acid pretreated type II energy cane had a higher ethanol yield after fermentation by Klebsiella oxytoca without enzymatic saccharification than 0.8 M and 1.6 M sulfuric acid pretreated type II energy cane. Pretreated biomass was inoculated with K. oxytoca for cellulose fermentation and Pichia stipitis for hemicellulose fermentation under simultaneous saccahrification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) conditions. For enzymatic saccharification of cellulose, the cellulase and ??-glucanase cocktail significantly increased ethanol production compared to the ethanol production of fermented acid pretreated energy cane without enzymatic saccharification. The results revealed that energy cane variety L 79-1002 produced maximum cellulosic ethanol under SHF (6995 mg/L) and produced 3624 mg/L ethanol from fermentation of hemicellulosic sugars.     

Genotypic Variations in Non-Structural Carbohydrate and Cell-Wall Components of the Stem in Rice,Sorghum, and Sugar Vane

We evaluated genetic variations in the non-structural carbohydrate (NSC) and the cell-wall components of stem in rice, sorghum, and sugar cane to assess the potential suitability of these gramineous crops for bioethanol production. For NSC, the maximum soluble sugar concentration was highest in sugar cane, followed by sorghum with sucrose. The major NSC in rice was starch, but there were wide variations in the starch to soluble sugar ratios among the cultivars. The total concentration of cell-wall components was negatively correlated with the NSC concentration, indicating competition for carbon sources. Among the cell-wall components, lignin was relatively stable within each group. The major sugar species composing hemicellulose was xylose in all crop groups, but there were differences in composition, with a higher fraction of arabinose and glucose in rice as compared to the other crops. In rice, there was less lignin than in sorghum or sugar cane; this might be advantageous for the efficient saccharification of cellulose.     

Bioconversion of sugar cane crop residues with white-rot fungiPleurotus sp.

Four mushroom strains ofPleurotus spp. were cultivated on sugar cane crop residues for 30 days at 26°C. Biochemical changes affected the substrate as a result of fungal growth, in terms of nitrogen, lignin, cellulose and hemicellulose contents. All strains showed a strong ligninolytic activity together with variable cellulolytic and xylanolytic action.Pleurotus sajor-caju attacked lignin and cellulose at the same rate, showing a degradation of 47% and 55%, respectively. A better balance was shown by theP. ostreatus-P. pulmonarius hybrid, which exhibited the poorest cellulolytic action (39%) and the highest ligninolytic activity (67%). The average composition of mushroom fruit bodies, in terms of nitrogen, carbohydrates, fats and amino acid profiles, was determined. Crude protein and total carbohydrate varied from 23% to 33% and 36% to 68% of dry matter, respectively. Fat ranged from 3.3% to 4.7% and amino acid content from 12.2% to 22.2%. Slight evidence for a nitrogen fixing capability was encountered in the substrate to fruit body balance.     

Enzymatic digestion of alkaline‐sulfite pretreated sugar cane bagasse and its correlation with the chemical and structural changes occurring during the pretreatment step

Sugar cane bagasse is recalcitrant to enzymatic digestion, which hinders the efficient conversion of its polysaccharides into fermentable sugars. Alkaline‐sulfite pretreatment was used to overcome the sugar cane bagasse recalcitrance. Chemical and structural changes that occurred during the pretreatment were correlated with the efficiency of the enzymatic digestion of the polysaccharides. The first 30 min of pretreatment, which removed approximately half of the initial lignin and 30% of hemicellulose seemed responsible for a significant enhancement of the cellulose conversion level, which reached 64%. After the first 30 min of pretreatment, delignification increased slightly, and hemicellulose removal was not enhanced; however, acid groups continued to be introduced into the residual lignin. Water retention values were 145% to the untreated bagasse and 210% to the bagasse pretreated for 120 min and fiber widths increased from 10.4 to 30 μm, respectively. These changes were responsible for an additional increase in the efficiency of enzymatic hydrolysis of the cellulose, which reached 92% with the 120 min pretreated sample. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:890–895, 2013     

Evaluation of sugar feedstocks for bio-based chemicals: A consequential,regionalized life cycle assessment

Fermentable sugars are an attractive feedstock for the production of bio-based chemicals. However, little is known about the environmental performance of sugar feedstocks when demand for sugars increases, and when local conditions and sensitivities of receiving ecosystems are taken into account. Production of monosaccharides from various first- and second-generation feedstocks (sugar beet, sugar cane, wheat, maize, wood, residual woodchips, and sawdust) in different geographic locations was assessed and compared as feedstock for monoethylene glycol (MEG) using consequential, regionalized life cycle assessment. Sugar cane grown in Thailand performed best in all three areas of protection, that is, for life cycle impacts on human health, ecosystem quality, and resources (respectively, equal to −7.6 × 10⁻⁵ disability-adjusted life years, −1.2 × 10⁻⁸ species-years and −0.046 US dollars per amount of feedstock needed to produce 1 kg of MEG). This was mainly due to benefits from by-products—incineration of sugar cane bagasse generating electricity and use of sugar cane molasses for the production of bioethanol. The wood-based feedstocks and maize performed worse than sugar cane and sugar beet, but their evaluation did not consider that sugar extraction technology from lignocellulose is immature, while identification of marginal suppliers of the marginal crop is particularly uncertain for maize. Wheat grown in Russia performed the worst mainly due to low agricultural yields (with impacts equal to 8.9 × 10⁻⁵ disability-adjusted life years, 6.9 × 10⁻⁷ species-years, and 1.8 US dollars per amount of feedstock required to produce 1 kg of bio-based MEG). Our results suggest that selection of sugar feedstocks for bio-based chemicals should focus on (i) the intended use of by-products and functions they replace and (ii) consideration of geographic differences in parameters that influence life cycle inventories, while spatial differentiation in the life cycle impact assessment was less influential.     

Enzyme hydrolysis and ethanol fermentation of dilute ammonia pretreated energy cane

This study is the first one ever to report on the use of high fiber sugarcane (a.k.a. energy cane) bagasse as feedstock for the production of cellulosic ethanol. Energy cane bagasse was pretreated with ammonium hydroxide (28% v/v solution), and water at a ratio of 1:0.5:8 at 160 °C for 1 h under 0.9-1.1 MPa. Approximately, 55% lignin, 30% hemicellulose, 9% cellulose, and 6% other (e.g., ash, proteins) were removed during the process. The maximum glucan conversion of dilute ammonia treated energy cane bagasse by cellulases was 87% with an ethanol yield (glucose only) of 23 g ethanol/100 g dry biomass. The enzymatic digestibility was related to the removal of lignin and hemicellulose, perhaps due to increased surface area and porosity resulting in the deformation and swelling of exposed fibers as shown in the SEM pictures.     

Degradation of sugar cane bagasse by several white-rot fungi

Forty-two white-rot fungi isolated in South America were incubated with long fibre sugar cane bagasse (LFB). The residual composition of LFB was determined after white-rot decay at 30 and 60 days. The ratio of residual lignin to residual lignin to residual cellulose (RL/RC) of untreated material (LFB) was 0.48. After white-rot-decay, the residual material with lower RL/RC ratios indicated that mainly lignin was degraded. In only 30 days, Phlebia sp. MVHC 5535, Athelia sp. MVHC 5509 and Spongipellis pachyodon MVHC 5019 caused a decrease in the RL/RC ratio to 0.36, 0.37 and 0.38, respectively, while it took 60 days for Ganoderma applanatum MVHC 5347, Hyphodontia sp. MVHC 5544, Panus tigrinus MVHC 5400, Stereum sp. MVHC 5113, Phellinus punctatus MVHC 5346 and MVHC 6388 to reach a ratio lower than 0.40. No correlation was found between the amount of some ligninolytic enzymes secreted and the residual composition of bagasse after white-rot fungi fermentation. Most of the fungal strains caused an increase in the relative amount of residual cellulose, indicating that hemicellulose was the preferred energy source.     

Pyrolysis of olive residue and sugar cane bagasse: non-isothermal thermogravimetric kinetic analysis

Thermal degradation and kinetics for olive residue and sugar cane bagasse have been evaluated under dynamic conditions in the presence of nitrogen atmosphere, using a non-isothermal thermogravimetric method (TGA). The effect of heating rate was evaluated in the range of 2-50 K min(-1) providing significant parameters for the fingerprinting of the biomass. The DTG plot for the olive residue and sugar cane bagasse clearly shows that the bagasse begins to degrade at 473 K and exhibits two major peaks. The initial mass-loss was associated with hemicellulose pyrolysis and responsible for the first peak (538-543 K) whereas cellulose pyrolysis was initiated at higher temperatures and responsible for the second peak (600-607 K). The two biomass mainly devolatilized around 473-673 K, with total volatile yield of about 70-75%. The char in final residue was about 19-26%. Mass loss and mass loss rates were strongly affected by heating rate. It was found that an increase in heating rate resulted in a shift of thermograms to higher temperatures. Ozawa-Flynn-Wall and Vyazovkin methods were applied to determine apparent activation energy to the olive residue and sugar cane bagasse. Two different steps were detected with apparent activation energies in the 10-40% conversion range have a value of 153-162 kJ mol(-1) and 168-180 kJ mol(-1) for the hemicellulose degradation of olive residue and sugar cane bagasse, respectively. In the 50-80% conversion range, this value is 204-215 kJ mol(-1) and 231-240 kJ mol(-1) for the cellulose degradation of olive residue and sugar cane bagasse, respectively.     

Life cycle assessment of cane-sugar on the island of mauritius

Goal, Scope and Background  Agricultural production includes not only crop production, but also food processing, transport, distribution, preparation, and disposal. The effects of all these must be considered and controlled if the food chain is to be made sustainable. The goal of this case study was to identify and review the significant areas of potential environmental impacts across the whole life cycle of cane sugar on the island of Mauritius. Methods  The functional unit was one tonne of exported raw sugar from the island. The life cycle investigated includes the stage of cane cultivation and harvest, cane burning, transport, fertilizer and herbicide manufacture, cane sugar manufacture and electricity generation from bagasse. Data was gathered from companies, factories, sugar statistics, databases and literature. Energy depletion, climate change, acidification, oxidant formation, nutrification, aquatic ecotoxicity and human toxicity were assessed. Results and Discussion  The inventory of the current sugar production system revealed that the production of one tonne of sugar requires, on average, a land area of 0.12 ha, the application of 0.84 kg of herbicides and 16.5 kg of N-fertilizer, use of 553 tons of water and 170 tonne-km of transport services. The total energy consumption is about 14235 MJ per tonne of sugar, of which fossil fuel consumption accounts for 1995 MJ and the rest is from renewable bagasse. 160 kg of CO₂ per tonne of sugar is released from fossil fuel energy use and the net avoided emissions of CO₂ on the island due to the use of bagasse as an energy source is 932,000 tonnes. 1.7 kg TSP, 1.21 kg SO₂,1.26 kgNO_xand 1.26 kg CO are emitted to the air per tonne of sugar produced. 1.7 kg N, 0.002 kg herbicide, 19.1 kg COD, 13.1 kgTSS and 0.37 kg PO₄ ^3- are emitted to water per tonne of sugar produced. Cane cultivation and harvest accounts for the largest environmental impact (44%) followed by fertilizer and herbicide manufacture (22%), sugar processing and electricity generation (20%), transportation (13%) and cane burning (1%). Nutrification is the main impact followed by acidification and energy depletion. Conclusions  There are a number of options for improvement of the environmental performance of the cane-sugar production chain. Cane cultivation, and fertilizer and herbicide manufacture, were hotspots for most of the impact categories investigated. Better irrigation systems, precision farming, optimal use of herbicides, centralisation of sugar factories, implementation of co-generation projects and pollution control during manufacturing and bagasse burning are measures that would considerably decrease resource use and environmental impacts. Recommendation and Outlook  LCA was shown to be a valuable tool to assess the environmental impacts throughout the food production chain and to evaluate government policies on agricultural production systems.     

Refining sweet sorghum to ethanol and sugar: economic trade-offs in the context of North China

Reducing the use of non-renewable fossil energy reserves together with improving the environment are two important reasons that drive interest in the use of bioethanol as an automotive fuel. Conversion of sugar and starch to ethanol has been proven at an industrial scale in Brazil and the United States, respectively, and this alcohol has been able to compete with conventional gasoline due to various incentives. In this paper, we examined making ethanol from the sugar extracted from the juice of sweet sorghum and/or from the hemicellulose and cellulose in the residual sorghum bagasse versus selling the sugar from the juice or burning the bagasse to make electricity in four scenarios in the context of North China. In general terms, the production of ethanol from the hemicellulose and cellulose in bagasse was more favorable than burning it to make power, but the relative merits of making ethanol or sugar from the juice was very sensitive to the price of sugar in China. This result was confirmed by both process economics and analysis of opportunity costs. Thus, a flexible plant capable of making both sugar and fuel-ethanol from the juice is recommended. Overall, ethanol production from sorghum bagasse appears very favorable, but other agricultural residues such as corn stover and rice hulls would likely provide a more attractive feedstock for making ethanol in the medium and long term due to their extensive availability in North China and their independence from other markets. Furthermore, the process for residue conversion was based on particular design assumptions, and other technologies could enhance competitiveness while considerations such as perceived risk could impede applications.     

QTL for fibre-related traits in grain × sweet sorghum as a tool for the enhancement of sorghum as a biomass crop

Compared to maize and temperate grasses, sorghum has received less attention in terms of improving cell wall components. The objectives of this study were to identify quantitative trait loci (QTL) with main effects, epistatic and pleiotropic effects along with QTL × environment (QE) interactions controlling fibre-related traits in sorghum. Neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose, hemicellulose, fresh leaf mass, stripped stalk mass, dry stalk mass, fresh biomass and dry biomass were analysed from a population of 188 grain × sweet sorghum recombinant inbred lines. A genetic map consisting of 157 DNA markers was constructed, and QTL were detected using composite interval mapping (CIM). CIM detected more than 5 additive QTL per trait explaining 7.1–24.7% of the phenotypic variation. Abundant co-localization of these QTL was observed across all chromosomes, and the highest cluster was identified on chromosome 6. Searching for candidate genes using the confidence interval of our QTL clusters reveals that these clusters might comprise a set of genes that are tightly linked. Some QTL showed multiple effects; however, the allele for each trait was favouring the parent with the increasing effect. QE interactions were observed for QTL showing multiple effects. Additive × additive interaction was observed for 7 out of 10 traits, indicating the importance of epistatic analysis. However, the phenotypic variation explained by digenic interactions was lower compared to the individual QTL. Our results indicate that various genetic components contribute to fibre-related traits and should be considered during the enhancement of sorghum for lignocellulosic biomass.     

Alkali‐based AFEX pretreatment for the conversion of sugarcane bagasse and cane leaf residues to ethanol

Sugarcane is one of the major agricultural crops cultivated in tropical climate regions of the world. Each tonne of raw cane production is associated with the generation of 130 kg dry weight of bagasse after juice extraction and 250 kg dry weight of cane leaf residue postharvest. The annual world production of sugarcane is ～1.6 billion tones, generating 279 MMT tones of biomass residues (bagasse and cane leaf matter) that would be available for cellulosic ethanol production. Here, we investigated the production of cellulosic ethanol from sugar cane bagasse and sugar cane leaf residue using an alkaline pretreatment: ammonia fiber expansion (AFEX). The AFEX pretreatment improved the accessibility of cellulose and hemicelluloses to enzymes during hydrolysis by breaking down the ester linkages and other lignin carbohydrate complex (LCC) bonds and the sugar produced by this process is found to be highly fermentable. The maximum glucan conversion of AFEX pretreated bagasse and cane leaf residue by cellulases was ～85%. Supplementation with hemicellulases during enzymatic hydrolysis improved the xylan conversion up to 95–98%. Xylanase supplementation also contributed to a marginal improvement in the glucan conversion. AFEX‐treated cane leaf residue was found to have a greater enzymatic digestibility compared to AFEX‐treated bagasse. Co‐fermentation of glucose and xylose, produced from high solid loading (6% glucan) hydrolysis of AFEX‐treated bagasse and cane leaf residue, using the recombinant Saccharomyces cerevisiae (424A LNH‐ST) produced 34–36 g/L of ethanol with 92% theoretical yield. These results demonstrate that AFEX pretreatment is a viable process for conversion of bagasse and cane leaf residue into cellulosic ethanol. Biotechnol. Bioeng. 2010;107: 441–450. © 2010 Wiley Periodicals, Inc.     

Ethanol production potential of sweet sorghum assessed using forage fiber analysis procedures

Sweet sorghum (Sorghum bicolor (L.) Moench) is widely recognized as a highly promising biomass energy crop with particular potential to complement sugarcane production in diversified cropping systems. Agronomic assessments have led to identification of four cultivars well suited for such sugarcane‐based production systems in southern Louisiana. Sweet sorghum biofuel production systems are currently being developed, and research producing large sample numbers requiring ethanol yield assessment is anticipated. Fiber analysis approaches developed for forage evaluation appear to be useful for screening such large numbers of samples for relative ethanol yield. Chemical composition, forage fiber characteristics, digestibility, and ethanol production of sweet sorghum bagasse from the four cultivars were assessed. Measures of detergent fiber, lignin, and digestibility were highly correlated with ethanol production (P < 0.01). The best linear regression models accounted for about 80% of the variation among cultivars in ethanol production. Bagasse from the cultivar Dale produced more ethanol per gram of material than any of the other cultivars. This superior ethanol production was apparently associated with less lignin in stems of Dale. Forage evaluation measures including detergent fiber analyses, in vitro digestibility, and an in vitro gas production technique successfully identified the cultivar superior in ethanol yield indicating their usefulness for screening sweet sorghum samples for potential ethanol production in research programs generating large sample numbers from evaluations of germ plasm or agronomic treatments. These screening procedures reduce time and expense of alternatives such as hexose sugar assessment for calculating theoretical ethanol yield.     

Simultaneous saccharification and co-fermentation of crystalline cellulose and sugar cane bagasse hemicellulose hydrolysate to lactate by a thermotolerant acidophilic Bacillus sp

Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 degrees C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 degrees C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid.     

Root dynamics in plant and ratoon crops of sugar cane

The root system of a sugar cane crop on an Ultisol in northeastern Brazil was examined throughout the plant and first ratoon crop cycles, using both coring and minirhizotron methods. Total root masses (living plus dead, 0.9–1.1 kg m^-2) and live root lengths (14.0–17.5 km m^-2) were greater during the ratoon cycle than at the end of the plant cane cycle (0.75 kg m^-2 and 13.8 km m^-2, respectively). Root die-back during the two weeks following ratoon harvest was estimated to be 0.15 kg m^-2, about 17% of the total root mass. Root die-back after the plant cane harvest was lower because fire was not used at this harvest and soil humidity was higher under the accumulated litter. A small amount of fine roots proliferated in the litter layer, amounting to 1% of the total mass and 3% of the total length. Root turnover could not be accurately assessed from minirhizotron observations due to variation in the relationship between coring data and the minirhizotron data with both time and soil depth.     

Fermentation of sugar cane bagasse hemicellulose hydrolysate to l(+)-lactic acid by a thermotolerant acidophilic Bacillus sp.**

Sugar cane bagasse hemicellulose, hydrolyzed by dilute H2SO4, supplemented with mineral salts and 0.5% corn steep liquor, was fermented to L(+)-lactic acid using a newly isolated strain of Bacillus sp. In batch fermentations at 50 degrees C and pH 5, over 5.5% (w/v) L(+)-lactic acid was produced (89% theoretical yield; 0.9 g lactate per g sugar) with an optical purity of 99.5%.     

Production of Pleurotus ostreatus mushrooms on sugar cane agrowastes

The growth of different strains of Pleurotus spp. on sugar cane agrowastes was evaluated. Three hybrid strains with good production outcomes and yields exceeding 17% were selected. Strain 184 (P. ostreatus x P. pulmonarius) showed the best results. Three spawn materials (wheat grain, millet grain and milled corn cob) at different spawning levels were tested and a significant influence was found. The obtained results were best explained in terms of total nitrogen content of the initial mixture (spawn + substrate), suggesting a probable nitrogen limited growth of the mushroom on sugar cane residues. A 10% millet grain spawn was found to be a reasonable compromise. Productive responses decreased with an increase in bag's capacity (8–10–12 kg), even though the same diameter was maintained in order to avoid pronounced temperature profiles. Smaller bag's capacities (8–10 kg) were recommended. It was also shown that the utilization of water hyacinth (Eichhornia crassipes) mixed 50/50 with sugar cane residues as substrate caused a twofold increase of crop responses, confirming the advantages of this substrate supplementation. The obtained results identified sugar cane agrowastes as a feasible substrate for Pleurotus spp. production with yields and biological efficiencies comparable and to some extent better than others reported with conventional lignocellulosic residues such as cereal straw.     

Ethanol from sugar crops

Soluble sugars, like sucrose, glucose and fructose, are transformed by yeast into ethanol and carbon dioxide. These sugars are stored in photosynthetically efficient plants like sugar cane. Recent developments in the transformation of sucrose present in sugar cane or sweet sorghum into ethanol, include the use of the Tilby machine, a high-temperature extraction process and the Ex-Ferm process. This review covers kinetic aspects of ethanol production, yeast immobilization techniques, yeast properties and fermentation byproducts.