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.     

Bagasse Silage from Sweet Pearl Millet and Sweet Sorghum as Influenced by Harvest Dates and Delays between Biomass Chopping and Pressing

Bagasse remaining after extracting the juice from crop biomass for ethanol production could be preserved as silage and used in animal feedstock, but the nutritive and conservation attributes of bagasse silage from sweet sorghum (Sorghum bicolor (L.) Moench) and sweet pearl millet (Pennisetum glaucum (L.) R.Br) are not well known. We evaluated the nutritive and conservation attributes of silages made with the bagasse of two species (sweet pearl millet and sweet sorghum) harvested on two dates (August and September) at two sites in Québec (Canada) and ensiled after four delays between biomass chopping and pressing (0.5, 2, 4, and 6 h). Bagasse silages made in laboratory silos were considered well preserved (pH?≤?4.0, NH₃-N?<?100 g kg^?1 total N, lactate?>?30 g kg^?1 DM, no propionic and butyric acids) regardless of species, harvest date, or delay between biomass chopping and pressing. Sweet pearl millet and sweet sorghum bagasse silages had similar total N concentration, in vitro true digestibility of dry matter (IVTD), and in vitro neutral detergent fiber digestibility (NDFD). Bagasse silage made from biomass harvested in August rather than in September had a 4 % greater concentration of total N, a 4 % greater IVTD, and a 8 % greater NDFD. The delay between biomass chopping and pressing did not affect the nutritive and conservation attributes of silages. Juice extraction from the biomass of sweet pearl millet and sweet sorghum did not impair attributes of good silage fermentation but it reduced its nutritive value.     

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.     

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.     

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.     

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.     

Agronomic Considerations for Sweet Sorghum Biofuel Production in the South-Central USA

Sweet sorghum (Sorghum bicolor (L.) Moench) is currently recognized throughout the world as a highly promising biomass energy crop. Production systems and management practices for sweet sorghum have not been fully developed for the USA, although sporadic research efforts during recent decades have provided some insights into production of sweet sorghum primarily for fermentable sugar production. Field plot experiments were conducted at sites across Louisiana to assess biomass and sugar yield responses to N fertilizer, plant density, and selected cultivars. Although linear increases in stem biomass production and fermentable sugar yield were obtained with increasing N fertilizer rate under irrigated conditions, most of the increase was from the initial 45 kg N ha⁻¹ increment. Nitrogen fertilization increased stem biomass production but not fermentable sugar yield in some non-irrigated environments. Increased plant density contributed to fermentable sugar yield only under growth-limiting conditions, particularly under limited soil moisture. Location effects indicate that sweet sorghum may not be suitable for some sub-optimal cropland and pasture environments in Louisiana. During the primary growing season, cultivar did not affect fermentable sugar yields, although Dale was consistently high in sugar concentration during this period. Nitrogen fertilizer increased fermentable sugar yields only when moisture was not limiting. Overall results indicate that in environments where soil moisture limits plant growth, sugar yield responses are likely from increased plant density and not from increased N fertilization.     

Evaluation of a Modular System for Low-Cost Transport and Storage of Herbaceous Biomass

A conceptual system adopting features from cotton, silage, and container shipping systems was evaluated between 2008 and 2011. The evaluation included both simulations of the anticipated full-scale system and field trials of forming, transporting, and storing biomass modules containing energy sorghum. The simulations utilized Integrated Biomass Supply Analysis and Logistics (IBSAL) and incorporated the anticipated module forming machine that would operate in partnership with a forage harvester, as well as a machine to load the modules onto a flatbed semi-trailer. When compared to the DOE target for logistics costs of $38.59/Mg, the estimated cost was lower for distances up to 80 km. Field results were promising, with biomass modules of up to 5.2 Mg formed, stored for up to 12 months, loaded on a truck in 2 min or less, and transported for 96 km with no significant change of shape or size. Difficulty in field drying of energy sorghum was consistent over 3 years of harvest, as was the ability to use field drying in windrows without increasing the ash content of the biomass. The manually formed module packages did not maintain an anaerobic environment throughout the storage period, and excessive biomass degradation occurred. In addition, the dry matter density in the modules was approximately 180 kg/m³ rather than the 240 kg/m³ targeted in the simulation. Despite the conceptual evaluation not achieving all the desired features, these studies demonstrated the economic and logistical advantages of a system based upon large packages of chopped biomass.     

The use of cytoplasmic male-sterility in hybrid seed production

The practical utilization of heterosis in crop plants has been greatly facilitated during the past 15 years by the use of cytoplasmic male|sterility for low-cost, large-scale emasculation of the seed parents of hybrids. The method is now being used in commercial production of hybrid onions, sugar beets, field corn, grain sorghum, and petunias. Its use is contemplated for hybrid sweet corn, pop corn, red table beets, fodder beets, fodder sorghum, pearl millet, carrots, and garden peppers.     

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.     

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.     

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。     

Optimizing Sweet Sorghum Production for Biofuel in the Southeastern USA Through Nitrogen Fertilization and Top Removal

Sustainable bioenergy cropping systems require not only high yields but also efficient use of inputs. Management practices optimizing production of sweet sorghum [Sorghum bicolor (L.) Moench] for bioenergy use are needed. The effects of N rate (45, 90, 135, and 180?kg N?ha^?1) and top removal (at boot stage, anthesis, and none) on biomass, brix, estimated sugar yield, and N and P recovery of sweet sorghum cv. M-81E were investigated in Florida at two sites differing in soil type. Across all data, dry biomass yields averaged 17.7 Mg?ha^?1 and were not affected by N fertilization rate at either site (P?>?0.10). Mean brix values ranged from 131 to 151?mg?g^?1 and were negatively related to N rate. Top removal, either at boot stage or anthesis, resulted in greater brix values and 13% greater sugar yields at both locations. Whole plant N recovery was positively and linearly related to N rate and ranged from 78 to 166?kg N?ha^?1, approximately two thirds of which was in leaf and grain tissues. Based on yield and nutrient recovery responses, optimal nutrient requirements were 90 to 110?kg N?ha^?1 and 15 to 20?kg P?ha^?1. Higher N fertilization led to greater N recovery, but little to modest gain in sugar yield. Thus, proper nutrient and harvest management will be needed to optimize sugar yields of sweet sorghum for production of biofuels and bio-based products. Further research is needed to refine management practices of sweet sorghum for bioenergy production, especially with regard to the use of leaf and grain tissues.     

Genetic diversity and population structure analysis of accessions in the US historic sweet sorghum collection

Sweet sorghum has the potential to become a versatile feedstock for large-scale bioenergy production given its sugar from stem juice, cellulose/hemicellulose from stalks, and starch from grain. However, for researchers to maximize its feedstock potential a first step includes additional evaluations of the 2,180 accessions with varied origins in the US historic sweet sorghum collection. To assess genetic diversity of this collection for bioenergy breeding and population structure for association mapping, we selected 96 accessions and genotyped them with 95 simple sequence repeat markers. Subsequent genetic diversity and population structure analysis methods identified four subpopulations in this panel, which correlated well with the geographic locations where these accessions originated or were collected. Model comparisons for three quantitative traits revealed different levels of population structure effects on flowering time, plant height, and brix. Our results suggest that diverse germplasm accessions curated from different geographical regions should be considered for plant breeding programs to develop sweet sorghum cultivars or hybrids, and that this sweet sorghum panel can be further explored for association mapping.     

L(+)-Lactic acid from sweet sorghum by submerged and solid-state fermentations

Sweet sorghum was used as the raw material for the lactate production by a strain of Lactobacillus paracasei. The submerged conversion of sugar juice obtained from sweet sorghum by extraction could be accomplished with the same efficiency as observed in a control experiment with MRS-glucose medium (final lactate concentration of 88–106 g/l, lactate yield of 91–95%, duration of the fermentation of 24–32 h). Finely ground stalks of sorghum served as the substrate in the solid-state fermentation. The lactate accumulation in the solid medium and the lactate yield were optimized up to values comparable with the results from the submerged fermentation (final lactate concentration of 90 g/kg, lactate yield of 91–95%). However, the duration of the fermentation amounted to 120–200 h in the solid-state process. The data from a series of experiments performed at variable values of temperatures between 30°C and 36°C and initial sugar concentrations between 60 g/kg and 115 g/kg, and degrees of moisture between 78% and 82% was the basis of a polynomial multidimensional regression. As a result, simple three-dimensional model functions were obtained for the maximum productivity of lactate formation, the lactate yield and the time required for a 90% conversion.     

Energy analysis of ethanol production from sweet sorghum

The Piedmont System is a collection of equipment for efficiently removing the juice from sweet sorghum stalks for the production of ethanol. The concept is to separate the whole stalks into pith and rind-leaf fractions, pass only the pith fraction through a screw press, and thus achieve an improvement in juice-expression efficiency and press capacity. An energy analysis was done for two options of this proposed harvesting/processing system: (Option 1) The juice is evaporated to syrup and used throughout the year to produce ethanol, and the by-products are used as cattle feed. (Option 2) The juice is fermented as it is harvested, and the by-products (along with other cellulosic materials) are used as feedstock for the remainder of the year. Energy ratios (energy output/energy input) of 0·9, 1·1 and 0·8 were found for sweet sorghum Option 1, sweet sorghum Option 2, and corn, respectively, as feedstocks for ethanol. If only liquid fuels are considered, the ratios are increased to 3·5, 7·9 and 4·5.     

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.     

Cofermentation of sweet sorghum juice and grain for production of fuel ethanol and distillers' wet grain

In an attempt to reduce the costs associated with fuel ethanol production from grain, the authors used sweet sorghum juice as a partial or complete replacement for tap-water in mash preparation and fermentation. This juice, which was an unutilized by-product of sweet sorghum silage preservation by the Ag-Bag method, contained 6·5–7·6% (wt/wt) reducing sugar and produced up to 3·51% (v/v) ethanol beers after fermentation. Varying amounts of this juice were mixed with water and corn or wheat, either before or after liquefaction (front-end or back-end loading, respectively). When over 60% juice replacement was used in front-end loading trials, salt buildup, due to required pH adjustments during cooking, inhibited yeast metabolism and thereby reduced yields. This inhibition was not observed during back-end loading trials since acid and base usage during cooking were reduced. However, in all trials we noted yeast inhibition by some factor(s) present in juice from sweet sorghum variety NK 8368. This inhibition was not observed with variety NK 405. If sweet sorghum juice is used to replace 40% of the water and either 12·5% of the corn or 12% of the wheat in mash preparation, production costs can be reduced by $0.032/liter ($0.12/US gallon) for corn and $0.040/liter ($0.15/US gallon) for wheat.     

Heat Shock Proteins of Sorghum [Sorghum bicolor (L.) Moench] and Pearl Millet [Pennisetum glaucum (L.) R.Br.] Cultivars with Differing Heat Tolerance at Seedling Establishment Stage

The production of heat shock proteins was compared in sorghumand pearl millet genotypes differing in seedling establishmentcharacteristics under heat stress. Two major heat shock proteins(hsps) of apparent mol. wt. 65 kD and 62 kD were seen in allthe genotypes of sorghum tested when the incubation temperatureof the 40 h seedlings was altered from 35 ?C to 45 ?C for 2h. Under identical conditions, pearl millet genotypes showedmore hsps and the apparent mol. wt. of these ranged from 30–70kD. The hsp bands were more prominent in whole seedlings androots as compared to plumules. Differences in the productionof hsps were seen in sorghum and pearl millet genotypes withcontrasting heat tolerance at seedling establishment stage butthe significance of these needs to be studied further. Key words: Heat shock proteins, sorghum, genotypic differences     

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.