Evaluation of theoretical ethanol production from forage sorghums (Sorghum bicolor L. Moench) in Sinaloa, Mexico

J. M. Moreno-Hernández1; T. Moreno-Gallegos1; J. A. López-Guzmán1

Correspondence: *. Corresponding Author: Tomás Moreno Gallegos, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias. Campo Experimental Valle de Culiacán. Km. 16.5 Carretera Culiacán-El Dorado. Culiacán. Sinaloa, México. Phone: +52 (553) 871 8700 ext. 81134. E-mail: E-mail:


Abstract

Sorghum is an emerging energetic crop for biofuel production under a sustainable approach, therefore assessments are required to identify varieties with adequate biomass production, juice quality and ethanol efficiency. In this research, commercial (Costeño-201, Fortuna, Gavatero-203, Matinal, Perla-101, RB-Paloma and Sinaloense-202) and experimental (Dulce, Mazatlan-16 and Variedad-2) varieties of forage sorghum were established under irrigation conditions in Sinaloa (plot located at 24°37’ 57.1” N and 107°26’ 32.3” O with an elevation of 19 m above sea level) to evaluate its period of industrial use (PIU), biomass efficiency and theoretical ethanol production. The varieties sowed during 2015-2016 autumn-winter cycle in Sinaloa showed a maximum solid content in juice higher than 11 °Brix, when going from flowering stage to softdough grain stage, being this PIU optimum for material harvesting. The most outstanding varieties correspond to sorghum of medium and medium-late vegetative cycles, with plant height between 1.9 and 2.4 m. The statistical analysis showed differences in biomass production (LSD= 1.7 t ha-1), being commercial (Fortuna, Sinaloense-202, Costeño-201 and Gavatero-203) and experimental (Dulce and Variedad-2) varieties the most outstanding with biomass efficiency higher than 55 t ha-1. When comparing theoretical ethanol efficiencies, significant differences (LSD= 152.3 L ha-1) were found among varieties, a theoretical ethanol production around 3,083-3,260 L ha-1 was estimated in Variedad-2, Mazatlan-16 experimental sorghums; as well as Costeño-201 and Gavatero-203 commercial varieties. These results evidenced the potential of forage sorghums as an alternative energetic crop to sugarcane or maize. New sorghum materials are needed to develop a bioenergy industry in the state of Sinaloa, allowing switching towards a more sustainable energetic system in the medium term.

Received: 2018 March 23; Accepted: 2018 July 4

revbio. 2018 Nov 27; 5(spe2): e483
doi: 10.15741/revbio.05.nesp.e483

Keywords: Key words: Biofuels, sorghum genetic improvement, theoretical etanol.

Introduction

Developing energetic alternatives to the use of fossil fuels as petroleum and its derivatives (gasoline, diesel) is a current necessity for Mexico; this situation emerges from the fluctuations in petroleum prices and crude oil reserves reduction, but also from the ecological impact entailing the immoderate use of non-renewable resources (Pérez & Venegas, 2017). With this current outlook, the interest for developing biofuels like ethanol from different crops and agricultural sub-products has emerged (Prasad et al., 2007). In ethanol production, maize (Zea mays) and sugarcane (Saccharum officinarum) stand out for their large volumes of biomass production. However, the drift of these foodstuffs towards bioethanol production in Mexico, involves, in a short and medium term, important consequences in food safety, especially facing the current food deficit (Shamah-Levy et al., 2017). In this context, sweet sorghum (Sorghum bicolor) may be an alternative or supplementary raw material for bioethanol production. Bioethanol production from sorghum results attractive due to its photosynthetic efficiency, tolerance to drought, growth in saline soils, adaptability to different edaphic environments and conditions; moreover it does not belong to basic grains for human food (Almodares & Hadi, 2009). Some varieties of sweet sorghum present fast growth, high yield and sugar accumulation in the stem (Fernandes et al., 2014) and its biomass may be processed by means of different technological approaches to ease its reconversion to ethanol (Partida-Sedas et al., 2017; Ahmad et al., 2018). According to Montes-García et al. (2010), in Mexico, sorghum varieties specialized for bioethanol production are scarce and therefore identifying commercial varieties presenting a good potential in yield and strengthening breeding programs is needed. Currently, genetic resources in germplasm banks are available where double purpose varieties (forage and grain) have been developed. In Sinaloa, Mexico, sorghum is a strategic crop, sowed in around 300 thousand ha in irrigation and temporal areas, highlighting forage sorghum production systems as a support to the local cattle industry (Hernández-Espinal et al., 2010) however, the potential of sorghum cultivated in the region for biofuel production systems has not been explored yet. As a result, the present work aims to identify forage sorghum varieties with potential for ethanol production under irrigation conditions in the state of Sinaloa.

Materials and methods

Sorghum materials and agronomic management

Seven commercial varieties of forage sorghum Costeño-201, Fortuna, Gavatero-203, Matinal, Perla-101, RB-Paloma and Sinaloense-202, plus three experimental varieties (Dulce, Mazatlan-16 y Variedad-2) were established under irrigation conditions. Sorghum were sowed on January, 15th of 2016 in a plot located in the Agronomic Experimental Station of INIFAP in Culiacan Valley (24°37’ 57.1” North latitude and 107°26’ 32.3” West longitude) in Sinaloa, Mexico. The area where the study was conducted presents Bs1 climatic characteristics, vertisol (clay loam) soil type and an elevation of 19 m above sea level. Seeds were treated with Thiodicarb, Carboxamide and Sulfoxaflor before sowing according to manufacturer’s recommendations. The field was fertilized with 150 kg ha-1 of urea in pre-sowing (64 unities of N). Agronomic and pests management were performance according to recommendations in the guide for sorghum production in the center region of Sinaloa (Moreno-Gallegos & Hernández-Espinal, 2011). After seedlings emergence, days of flowering (when 50 % of plants present polen production), plant height and general crop safety were recorded.

Biomass production

Biomass yield was obtained by manually harvesting a 5 m section in two central furrows of the experimental unit. Harvest was realized when plants were in soft-dough grain stage (Phase 7; P7). Weight was recorded by means of a Mechanical Dial Hanging Scale (SALTER 235 10x model, England).

Solid content

One linear meter of plants was harvested to assess the sugar accumulation during anthesis (P6), postanthesis (soft-dough grain; P7) and maturity (P9) sorghum phenological stages, according to the phenology described by Vanderlip & Reeves (1972). After removing foliage, the stem was manually ground to obtain juice. Juice solid content (°Brix) was recorded by means of an optic refractometer (Sper Scientific, China) with a reading range of 0-32 °Brix.

Theoretical ethanol yield

Harvested material for biomass evaluation was used to measure stem juice volume. After determining solid concentration (°Brix), theoretical ethanol yield (Ethanolt) was estimated using the model reported by Bunphan et al. (2015) for yeast fermentation with Saccharomyces cerevisiae (Equation 1). This model uses a correction in sugar content metabolizable by yeast from juice solid content, subtracting 3° Brix and adjusting sugar concentration with its specific density at 20 °C (1.05). The model also considers that only 70% of solids in juice are metabolizable sugar (Am), from which 20 % is transformed into structural components of yeast biomass and 80 % is converted directly into ethanol with a conversion rate (Tc) of 0.53 L ethanol kg-1 of sugar.


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Statistical analysis

A yield biomass test was established by means of a Randomized Complete Block Design with three repetitions for green forage yield variable (t ha-1), where the experimental unit consists of 4 furrows of 5 m long (0.8 m distance between furrows) and a useful plot of 8 m2. For ethanol theoretical yield variable (L ha-1), a Randomized Complete Block Design was used with three replicates. The relationships between plant height-°Brix and plant heightbiomass were estimated by means of Pearson correlation coefficient. Statistical analysis and mean comparison by Least Significant Difference (LSD Fisher) was realized with the Statistical Analysis System version 9.2 software (SAS, 2009) at α=0.05.

Results and discussion

Sugar variation in stem

With the purpose of evaluating the ideal phenological stage for harvesting the different varieties of sorghum cultivated under irrigation conditions in Sinaloa, soluble solid content in stem juice (°Brix) for each material was determined during the anthesis (flowering, P6), post-anthesis (soft-dough grain; P7) and maturity (P9) phenological stages. Figure 1 shows °Brix variation from anthesis until the maturity of physiological material. During flowering, materials presented a solid concentration in juice of 8.0-10.0 °Brix, while in the softdough grain stage, solid content ranged between 11 and 13.8 °Brix, this variation corresponds to an increase of 25 % of solids regarding flowering for materials as Costeño-201, Matinal, Gavatero-203, Mazatlan-16 and Variedad-2, in which a maximum solid content was observed. With the progression of crop to maturity stage, a reduction in juice solid content was observed (around 17 %, regarding the soft-dough grain stage), however, solid content was higher than 10°Brix in some varieties. Different studies evidenced a fast solid accumulation (mainly sugars) in sorghum stem juice during plant physiological changes and its dependency with cultivar genotypic traits (Ratnavathi et al., 2010; Davila-Gomez et al., 2011). According to Almodares & Hadi (2009) nonstructural carbohydrates (glucose, fructose, sucrose) are being affected during grain filling and maturity, as well, temperature photoperiod and nutritional management influence in stem sugar content. Davila-Gomez et al. (2011) evaluated three varieties of sweet sorghums and two forage sorghums in Northeastern Mexico under irrigation conditions, recording an average accumulation of 2°Brix per week and reaching a maximum of 16°Brix in the 5th week post-anthesis in all cultivars. In addition, Fernandes et al. (2004) reported a fast sugar accumulation in the first 40 days post-anthesis and evidenced a 30 % reduction in sugar concentration at physiological maturity of sorghum. According to these authors, economically viable ethanol production from sorghum may be achieved when crops reach their maximum solid content in juice (14-16°Brix) or above 140 g L-1 of total sugars, therefore defining the optimal time for harvesting or period of industrial use (PIU) (Fernandes et al., 2014). In this context, solid variation in juice of the evaluated cultivars suggests a PIU corresponding to the step where cultivars were found in a soft-dough grain stage (around 70-85 days, depending of the variety).


[Figure ID: f1] Figure 1.

Variation of soluble solids in stem juice. Phonological stages: anthesis or flowering (P6), soft dough (P7) and maturity (P9).


Agronomic traits and biomass production

Evaluated sorghum varieties in the present study correspond to sorghum of intermediary cycle (6064 days of flowering) excepted Matinal and Perla-101, early varieties in which pollen production in 50 % of plants is reached at 53 and 57 days post-sowing, respectively (Table 1). Differences in the vegetative cycle importantly influence in plant traits and its productive potential; materials with prolonged vegetative cycle (late sorghums) develop higher internode length, internodes numbers and increased foliar area than early sorghums (i.e. increasing the photosynthetically active surface), than contributes to sugar production and biomass construction (Zhao et al., 2009). According to variance analysis, significant differences were found in biomass production among varieties. The highest biomass was recorded in intermediate-late cycle sorghums varieties Fortuna (65.01 t ha-1) and Sinaloence-202 (64.68 t ha-1), and the lowest one was recorded for the early sorghum Matinal (44.06 t ha-1). It has been established that late flowering sorghum varieties are generally taller; when extending the maturity period, the plant develops a higher number of internodes with higher length, showing an increase in biomass production (Murray et al., 2009; Burks et al., 2013). Similarly, Shukla et al. (2017) found a positive correlation between plant height and sugar concentration, finding out that intermediate-late genotypes show sugar content in stem significantly higher than early sorghums. In this study, a positive correlation was found between plant height and biomass (Pearson coefficient r2=0.1093), but not for plant height and solid content (°Brix) relation, as shown in Figure 2.

Table 1.

Agronomic traits and biomass production of forage sorghums


Variety Days to flowering Vegetative cycle Plant height (m) Biomass* (t ha-1)
Costeño-201 63 Medium 1.70 55.31 cd
Fortuna 68 Medium-late 1.95 65.01 a
Gavatero-203 62 Medium 2.04 55.62 cd
Matinal 53 Early 1.96 44.06 g
Perla-101 57 Early-medium 1.61 46.87 f
RB-Paloma 61 Medium 1.70 50.31 e
Sinaloense-202 64 Medium 1.89 64.68 a
Dulce 60 Medium 2.40 57.81 b
Mazatlan-16 62 Medium 1.63 54.68 d
Variedad-2 63 Medium 1.96 56.56 bc
C.V. (%) 4.25
LSD (t ha-1) 1.703

TFN1*Biomass correspond to forage yield for each variety. Means with different letter(s) are significantly different (at p≤0.05).



[Figure ID: f2] Figure 2.

Correlation between plant height-solid concentration and plant height-biomass in forage sorghums. Regression lines (dotted lines for °Brix and continuous line for biomass) and Pearson correlation coefficient (R2) for each relation are show in boxes inserted in graphic.


Theoretical ethanol yield of forage sorghum

With the purpose of determining ethanol potential production from sorghum juice, yield of juice extracted from the stem of vegetal material harvested in P7 stage was quantified, since sorghum in this phenological stage produce a juice with higher solid concentrations (°Brix). Stem-extracted juices have a sugar concentration (adjusted from °Brix) range between 75 and 112 g L-1. Sorghums Matinal, Variedad-2, Costeño-201, Gavatero-203 and Mazatlan-16 were the most attractive materials, that showed sugar contents over 100 g L-1 in stem juice (Table 2). Stem juice yield for the different forage sorghum varieties oscillated between 10,160 and 14,500 L ha-1, these yields were lower than those reported by Dávila-Gómez et al. (2011), who recorded yields between 15,000 and 28,300 L ha-1 for sweet sorghum varieties. For theses reason, sweet sorghums have been preferred over forage or grain producing sorghums to bioethanol industry (Capecchi et al., 2017). In the evaluation of theoretical ethanol yield, significant differences were found among sorghum varieties. Materials with a higher theoretical ethanol yield were Variedad-2, Gavatero-203, Mazatlan-16 and Costeño-201 with theoretical yields between 3,085 and 3,260 L ethanol ha-1. The lowest theoretical ethanol yield was recorded for Perla-101 with 2115 L ethanol ha-1 (Table 2). Theoretical ethanol yield in this study is comparable to ethanol productive potential estimated for maize and sugarcane crops, with volumes around 4,023 and 4,656 L ethanol ha-1, respectively (Schwietzke et al., 2009; Dhaliwal et al., 2011). Other hand, Zhang et al. (2010) reported yields of 3,750-4,700 L ha-1 for specialized sweet sorghum genotypes (sorghum with until 22° Brix in juice). Although ethanol experimental yield may differ from theoretical yield due to intrinsic factors during fermentation process, the different models used to estimate ethanol potential presented a high correlation (0.93<r<0.95) with real ethanol yield (Bunphan et al., 2015), therefore represent a valid approach to evaluate both forage and grain producing sorghum. Recently, Cole et al. (2017) evaluated the potential of commercial sweet sorghum genotypes under irrigation conditions, obtaining theoretical yields between 5,200 and 7,200 L ethanol ha-1, these yields are higher than those found in the present study. A more detailed analysis of sugar composition of the juice and and its scale-up to pilot fermentative process, will allow to establish the real potential of these forage sorghum varieties for ethanol production in Sinaloa; further studies are required to quantify ethanol production from juice as well as from biomass.

Table 2.

Juice yield and theoretical ethanol yield from forage sorghums


Variety Total sugar* (g L-1) Juice yield (L ha-1) Ethanol production (L ha-1)
Costeño-201 104 11,400 3,085 b
Fortuna 75 14,500 2,723 c
Gavatero-203 108 10,350 3,189 ab
Matinal 112 10,160 2,721 c
Perla-101 75 11,230 2,115 f
RB-Paloma 79 12,050 2,324 e
Sinaloense-202 78 14,480 2,782 c
Dulce 75 13,840 2,496 d
Mazatlan-16 105 11,030 3,086 b
Variedad-2 109 11,250 3,260 a
C.V. (%) 1.58

TFN2*Correspond to sugar content adjusted from °Brix in steam juice. Means with different letter(s) are significantly different (at p≤0.05).


Conclusion

Ccommercial varieties Costeño-201 and Gavatero-203; as well as experimental varieties Dulce, Mazatlan-16 and Variedad-2 of forage sorghums presented attractive plant traits, biomass and ethanol yield for biofuels production. To harvest the sorghums with highest concentration of solids and sugars in juice (>°11 Brix), the period of industrial use of materials corresponds to soft-dough grain (P7 stage) of plant development. Maximum ethanol yield calculated at the first harvest was of 3,260 L ha-1 (Variety-2); nevertheless, improved yields is possible if a second harvest is considered by material with good regrowth capacity under adequate agronomic management. Biomass production of forage sorghum may be considered for second generation ethanol production, increasing ethanol potential yield. Finally, it is necessary to encourage the sorghum breeding programs to generate new sorghum varieties with attractive plant traits to biofuel industry to facilitate the transition towards a sustainable energetic system in Mexico.


fn1Cite this paper: Moreno-Hernández J. M., Moreno-Gallegos T., López-Guzmán J. A. (2018). Evaluation of theoretical ethanol production from forage sorghums (Sorghum bicolor L. Moench) in Sinaloa, Mexico. Revista Bio Ciencias 5(nesp), e483. doi: https://doi.org/10.15741/revbio.05.nesp.e483

Acknowledgements

To Fundación Produce Sinaloa, A.C. for the economic support of the project entitled “Generating technology of sorghum varieties and hybrids for seasonal and irrigation in Sinaloa”. We thank to Octavio Macías and Lorenzo Vega for their extraordinary collaboration in sorghum breeding program.

References
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