Ethanol Conversion Efficiency Research Articles

Green Macroalgae Hydrolysate for Biofuel Production: Potential of Ulva rigida

In this study, the green macroalgae Ulva rigida, which contains 34.9% carbohydrates, underwent treatment with commercial hydrolytic enzymes. This treatment yielded a hydrolysate that contained 23 ± 0.6 g·L−1 of glucose, which was subsequently fermented with Saccharomyces cerevisiae. The fermentation process resulted in an ethanol concentration of 9.55 ± 0.20 g·L−1. The optimal conditions for ethanol production by S. cerevisiae were identified as follows: non-sterilized conditions, an absence of enrichment, and using an inoculum size of 118 mg·L−1. Under these conditions, the fermentation of the green macroalgal hydrolysate achieved a remarkable conversion efficiency of 80.78%. The ethanol o/t ratio, namely the ratios of the experimental to theoretical ethanol produced, for Scheffersomyces stipitis, Candida guilliermondii, Kluyveromyces marxianus, and S. cerevisiae after 48 h of fermentation were 52.25, 63.20, 70.49, and 82.87%, respectively. Furthermore, S. cerevisiae exhibited the best outcomes in terms of ethanol production (9.35 g·L−1) and conversion efficiency (80.78%) after 24 h (optimal time) of fermentation.

Coriolus versicolor laccase-based inorganic protein hybrid synthesis for application in biomass saccharification to enhance biological production of hydrogen and ethanol

In this study, a bio-friendly inorganic protein hybrid-based enzyme immobilization system using partially purified Coriolus versicolor laccase (CvLac) was successfully applied to biomass hydrolysis for the enhancement of sugar production aimed at generating biofuels. After four days of incubation, the maximum CvLac production was achieved at 140 U/mg of total protein in the presence of inducers such as copper and wheat bran after four days of incubation. Crude CvLac immobilized through inorganic protein hybrids such as nanoflowers (NFs) using zinc as Zn3(PO4)2/CvLac hybrid NFs (Zn/CvLac-NFs) showed a maximum encapsulation yield of 93.4% and a relative activity of 265% compared to free laccase. The synthesized Zn/CvLac-NFs exhibited significantly improved activity profiles and stability compared to free enzymes. Furthermore, Zn/CvLac-NFs retained a significantly high residual activity of 96.2% after ten reuse cycles. The saccharification of poplar biomass improved ∼2-fold in the presence of Zn/CvLac-NFs, with an 8-fold reduction in total phenolics compared to the control. The Zn/CvLac-NFs treated biomass hydrolysate showed high biological hydrogen (H2) production and ethanol conversion efficiency of up to 2.68 mol/mol of hexose and 79.0% compared to the control values of 1.27 mol of H2/mol of hexose and 58.4%, respectively. The CvLac hybrid NFs are the first time reported for biomass hydrolysis, and a significant enhancement in the production of hydrogen and ethanol was reported. The synthesis of such NFs based on crude forms of diverse enzymes can potentially be extended to a broad range of biotechnological applications.

Triticale and sorghum as feedstock for bioethanol production via consolidated bioprocessing

Corn starch is currently the primary feedstock for bioethanol production, but concerns about food security have prompted the evaluation of alternative cereals as feedstock. Two potential candidates, triticale and sorghum, can be grown on marginal farming land and mainly serve as animal feed. This study assessed flour and bran-like fractions of triticale and sorghum grains as feedstocks for bioethanol production using a consolidated bioprocessing approach. A Saccharomyces cerevisiae Ethanol Red™-derived amylolytic strain (ERT12) achieved ethanol conversion efficiencies of 100 and 96% from sorghum (after 96 h) and triticale flour (after 168 h), respectively. Supplementation with 10% of the recommended STARGEN™ 002 enzyme loading halved the fermentation time for sorghum and triticale flour. The raw starch in sorghum flour was more digestible than in triticale flour under consolidated bioprocessing conditions, whereas simultaneous saccharification and fermentation proved more effective for triticale flour. The two substrates also showed different hydrolysis patterns, which may be linked to their amylopectin content. This study demonstrated that both substrates could be converted to ethanol using only an efficient amylolytic strain without nitrogen supplementation. However, process development for biofuel production may require different fermentation configurations to be optimised for each substrate.

Ensiling pretreatment fortified with laccase and microbial inoculants enhances biomass preservation and bioethanol production of alfalfa stems.

This study investigated the potential of ensiling pretreatment fortified with laccase and a lactic acid bacteria (LAB) inoculant on improving the utilization of alfalfa stems for bioethanol production. The alfalfa stems were ensiled with no additives (Con), 0.04 % laccase (LA), a LAB inoculant containing Pediococcus pentosaceus at 1 × 106 fresh weight (FW) and Pediococcus acidilactici at 3 × 105 cfu/g FW (PP), and a combination of LA and PP (LAP) for 120 days. By reshaping the bacterial community structure of alfalfa stem silages toward a higher abundance of Lactobacillus, the addition of laccase and LAB inoculant either alone or in combination facilitated lactic acid fermentation to reduce fermentation losses, as evidenced by low concentrations of ammonia nitrogen (53.7 to 68.9 g/kg total nitrogen) and ethanol (2.63 to 3.55 g/kg dry matter). All additive treatments increased lignocellulose degradation and soluble sugars concentrations of alfalfa stem silages. Due to delignification and polyphenol removal, glucan and xylan conversion (70.3 % vs. 35.7 % and 51.6 % vs. 27.9 %, respectively) and ethanol conversion efficiency (53.9 % vs. 26.4 %) of alfalfa stems were greatly increased by ensiling fortified with LA versus Con, and these variables (79.8 % for glucan, 58.7 % for xylan, and 60.1 % for ethanol conversion efficiency) were further enhanced with a synergistic effect of LA and PP fortification. The spearman correlation analysis revealed that bioethanol fermentation of silage biomass was closely related to ensiling parameters and total phenols. In conclusion, ensiling pretreatment with LA and PP combination offered a feasible way to efficient utilization of alfalfa stems for bioethanol production.

Full components conversion of lignocellulose via a closed-circuit biorefinery process on a pilot scale

This study developed a closed-circuit biorefinery process for full conversion of lignocellulose into ethanol, biogas and organic fertilizer with zero waste on a pilot scale. In the process, subcritical water pretreatment could effectively break the structure of wheat straw (WS), and ethanol was obtained from pretreated wheat straw (PWS) using two batches of simultaneous saccharification and fermentation (SSF). The pretreatment and ethanol fermentation wastes were reused for biogas and organic fertilizer production by anaerobic digestion (AD), whereas the pretreatment and ethanol conversion efficiency were reduced when supernatant after AD was recovered for next batch pretreatment. The yields of ethanol (0.08–0.09 g/g), biogas (0.05–0.10 L/g) and organic fertilizer (0.55–0.79 g/g) were demonstrated through mass balance. Furthermore, the hidden problems were exposed on pilot-scale conversion process, and several strategies were provided for optimizing the biorefinery process in the future.

Strategy of electron acceptors for ethanol-driven chain elongation from kitchen waste

A two-phase kitchen waste (KW) fermentation was proposed in the current study to enhance medium-chain fatty acids (MCFAs) production from kitchen waste. In particular, effect of acetate to butyrate ratio (ABR) on MCFAs production was investigated which can be regulated by different pH and organic loading during the acidification phase. Medium ABR (1.00) was obtained when pH is 5.5 and organic loading is 20 g VS/L in FW acidification fermentation. Subsequent chain elongation fermentation demonstrated that the highest yield of caproate 9.67 g/L with selectivity of 79 %, and highest ethanol conversion efficiency of 1.11 was achieved in medium ABR system. Microbial community study showed that medium ABR significantly enrich the functional bacteria especially Clostridium kluyveri. The study provides a new method for chain elongation enhancement without addition of other additives in kitchen waste fermentation system and gives a guide for the regulation of the short-chain fatty acids distribution in its acidification phase.

Bioethanol production from biodegradable wastes using native yeast isolates from Ethiopian traditional alcoholic beverages

Due to the existing energy crisis and scarcity of conventional supplies of fossil fuels, there is a strong desire for the production of bioethanol from sustainable biodegradable waste as an alternative energy source. The aim of this study was to produce bioethanol from grain waste flour (GWF), Tella spent (TS), pineapple (PAP) and papaya peels (PYP) using native yeasts isolated from Ethiopian traditional alcoholic beverages. Diluted H2SO4 was used to hydrolyze polysaccharides in the waste materials. Starch content from GWF and reducing sugar concentration from each hydrolysate were determined by the standard protocol. Seventy-five native yeasts were isolated from local beverages for ethanol production. The 2% H2SO4 pretreatment produced the highest reducing sugar of GWF (30.1%); PYP (28.6%); PAP (16.4%); and TS (10.4%). In addition to this, GWF had 60.6% starch content. Of 75 isolates, 12 were able to tolerate ≥8% ethanol concentration, and 2 isolates, Y10 and Y55 showed strong ethanol production capacity (glucose to ethanol conversion efficiency) with 8.2% (79.8%) and 9.6% (94.3%) from synthetic medium, respectively. The highest ethanol yields of 16.1%, 9.8%, 8.0% and 6.1% were produced from GWF, PAP, PYP and TS, respectively using isolate, Y55 (identified as S. cerevisiae) within 168 h for GWF, 120 h for PAP and 72 h for PYP and TS. This study revealed that native yeast isolates could be used for industrial production of bioethanol via cheap biodegradable wastes.

Non-digesting strategy for efficient bioconversion of cassava to bioethanol via mechanical activation and metal salts pretreatment

This study focused on the development of an efficient technology for bioconversion of cassava to bioethanol without high temperature digesting. Mechanical activation (MA, ball milling)-metal salt (MA-MS) technology was applied to pretreat cassava flour, leading to significant changes in crystal structure, morphology, and viscosity. The destruction of stable structure of cassava flour induced by MA-MS pretreatment increased the accessibility of glucoamylase to starch granules from surface to interior, which contributed to direct and efficient saccharification of cassava flour without digesting. The decrease in viscosity of slurry and the use of metal salt as nutrient for yeast (Saccharomyces cerevisiae) had favorable effect on fermentation process. The combination of MA and MgSO4 exhibited outstanding synergistic interaction. The ethanol concentration and conversion efficiency of MA-MgSO4 pretreated cassava flour achieved 13.64 vol% and 93.4% under optimum conditions (addition amount of MgSO4 = 6 wt%, MA time = 75 min, dosage of glucoamylase = 200 U/g cassava, and dosage of Saccharomyces cerevisiae = 0.3 wt%). MA-MS pretreatment significantly enhanced the saccharification and fermentation processes for efficient bioconversion of cassava to bioethanol by non-digesting strategy.

W2C-Supported PtAuSn—A Catalyst with the Earliest Ethanol Oxidation Onset Potential and the Highest Ethanol Conversion Efficiency to CO2 Known till Date

The electrocatalytic behavior of a tungsten carbide-supported Pt(3 wt %)Au(3 wt %)Sn(10 wt %) catalyst (PtAuSn/W2C) is investigated toward the oxidation of ethanol at temperatures below 70 °C. Vulc...

Augmented hydrolysis of acid pretreated sugarcane bagasse by PEG 6000 addition: a case study of Cellic CTec2 with recycling and reuse.

In an integrated lignocellulosic biorefinery, the cost associated with the "cellulases" and "longer duration of cellulose hydrolysis" represents the two most important bottlenecks. Thus, to overcome these barriers, the present study aimed towards augmented hydrolysis of acid pretreated sugarcane bagasse within a short span of 16h using Cellic CTec2 by addition of PEG 6000. Addition of this surfactant not only enhanced glucose release by twofold within stipulated time, but aided in recovery of Cellic CTec2 which was further recycled and reused for second round of saccharification. During first round of hydrolysis, when Cellic CTec2 was loaded at 25mg protein/g cellulose content, it resulted in 76.24 ± 2.18% saccharification with a protein recovery of 58.4 ± 1.09%. Filtration through 50KDa PES membrane retained ~ 89% protein in 4.5-fold concentrated form and leads to simultaneous fractionation of ~ 70% glucose in the permeate. Later, the saccharification potential of recycled Cellic CTec2 was assessed for the second round of saccharification using two different approaches. Unfortified enzyme effectively hydrolysed 67% cellulose, whereas 72% glucose release was observed with Cellic CTec2 fortified with 25% fresh protein top-up. Incorporating the use of the recycled enzyme in two-stage hydrolysis could effectively reduce the Cellic CTec2 loading from 25 to 16.8mg protein/g cellulose. Furthermore, 80% ethanol conversion efficiencies were achieved when glucose-rich permeate obtained after the first and second rounds of saccharification were evaluated using Saccharomyces cerevisiae MTCC 180.

Deployment of SNP (CAPS and KASP) markers for allelic discrimination and easy access to functional variants for brown midrib genes bmr6 and bmr12 in Sorghum bicolor

The brown midrib (bmr) phenotype is a recessive trait of sorghum (Sorghum bicolor L. Moench) that results in overall lignin reduction and is associated with enhanced ruminant digestibility and increased feedstock to ethanol conversion efficiency. The three cloned Bmr loci encode genes involved in the monolignol biosynthetic pathway. There are eight known bmr loci in sorghum, but the two widely known are bmr6 and bmr12. A number of sorghum cultivars are referred to as bmr, but there is limited information as to their specific grouping, and it is important that new bmr lines in the pipeline can be easily genetically characterized. Hence, this study was performed to translate the genetic and DNA sequence information for bmr6 and bmr12, for use in the biomarker technology of single-nucleotide polymorphisms (SNPs). Through an analysis of variation for the two bmr genes, DNA markers in the form of cleave amplified polymorphic sequence (CAPS) and Kompetitive Allelele Specific Polymerase chain reaction (KASP) SNP markers were developed. The utility of the DNA markers for rapid and accurate identification of bmr6 or 12 individuals at the seedling stage were validated in a group of sorghum germplasm and a genetic population through marker-assisted selection. Two CAPS DNA markers (one each for bmr6 and 12) were evaluated and found to positively identify lines that harbor the different bmr genes. Fifteen KASP SNP markers (six for bmr6 and nine for bmr12) were developed and utilized for allelic discrimination and selection of bmr individuals at the seedling stage. The KASP marker bmr6-132 positively identified bmr6-ref allele among materials evaluated and individuals of segregating F2 population at the seedling stage. The KASP DNA marker bmr12-129, positively identified germplasm among materials evaluated and individuals of the F2 population at the seedling stage to select plants that carry the bmr12-ref allele . Results from this study also classified two sorghum germplasm as bmr12 and these lines can be utilized as specific donor of this bmr class using marker-assisted selection. This work demonstrated the successful translation and deployment of molecular information into specific CAPS and KASP DNA markers that are easy to access and can be applied in a breeding program, for use in efficient marker-assisted selection of bmr in sorghum.

Preheating Followed by Simultaneous Viscosity Reduction, Hydrolysis, and Fermentation: Simplifying the Process of Ethanol Production from Sweet Potato

In traditional methods, the ethanol production from starchy raw materials includes the stages of viscosity reduction, full hydrolysis, and fermentation, which are carried out in two or more steps. We propose to perform all these steps together with the method called P-SVHF (preheating followed by simultaneous viscosity reduction, hydrolysis, and fermentation). The sweet potato starch was hydrolyzed by applying a commercial enzyme mixture specially developed to degrade granular starch. Nevertheless, when starch was previously gelatinized, the ethanol production was 52% higher than that in which starch was in the granular form. Thus, the proposed method (P-SVHF) also includes the starch gelatinization stage (preheating). In the P-SVHF method, energy is saved through (i) reducing the mass that is heated (only sweet potatoes), and (ii) applying a temperature (76 °C) which is lower than what is usually used during the liquefaction (≥ 85 °C), then an energy saving of 48% in comparison with traditional methods was estimated. After the method definition, a central composite design was carried out to evaluate the influence of pH, temperature, and time in the SVHF. The significant contributions of the optimization were the time reduction, i.e., from 24 h to 18–19 h, and the ethanol conversion efficiency increased to about 93%.

Chemical composition analysis of various genetically modified sorghum traits: Pretreatment process optimization and bioethanol production from hemicellulosic hydrolyzates without detoxification

Compared to other inedible agricultural based feedstocks such as corn stover, rice husk, wheat straw and sugarcane bagasse, sorghum biomass (stalks and leaves) possess elevated credentials towards biofuel production which is highly tolerant against heat and drought conditions. Therefore, a novel sorghum phenotype was generated through genetic mutations called “brown midrib” which possesses low lignin content with enriched palatability. In the present study, the chemical composition of fourteen genetically modified sorghum biomass traits were analyzed which constitute, 52.7–60% of structural carbohydrates (cellulose and hemicellulose) and 11.6–17.7% of lignin. Due to the presence of low lignin content, pretreatment was performed using low energy input system to achieve maximum hemicellulose hydrolysis with minimized levels of sugar decomposition products. As a result, 88–92% of hemicellulose hydrolysis was attained with low amount of furfural (0.34–0.49 g/L) and 5-Hydroxymethylfurfural (0.38–0.56 g/L). Furthermore, fermentation was also performed without detoxification of pretreatment derived hemicellulosic hydrolyzate to evaluate the effect of fermentative inhibitors on ethanol-producing yeast. As a result, 88.8–92.5% ethanol conversion efficiency and 0.45–0.47 (gp/gs) ethanol yield were achieved within 15 h of fermentation time period.

Field response of near‐isogenic brown midrib sorghum lines to fusarium stalk rot, and response of wildtype lines to controlled water deficit

To increase digestibility for ruminant livestock and for lignocellulosic ethanol conversion efficiency in sorghum (Sorghum bicolor), brown midrib (bmr) lines carrying bmr6 or bmr12 and the double mutant (bmr6 bmr12) in two backgrounds (RTx430 and Wheatland) were developed, resulting in lines with significantly reduced lignin, as compared with the near‐isogenic wildtype. Under greenhouse conditions, these lines had previously demonstrated no increased susceptibility, and some lines were more resistant to the highly virulent stalk rot pathogen, Fusarium thapsinum, compared to the wildtype. Fusarium stalk rot of sorghum is a destructive disease that under high temperatures or drought conditions may lead to lodging. To determine if greenhouse observations could be extended to field environments, bmr and near‐isogenic wildtype lines were inoculated with F. thapsinum at field locations, Mead (irrigated) and Havelock (dryland) in Nebraska, USA. Analysis of mean lesion lengths showed those of most bmr lines were statistically similar to the wildtype. Across both genetic backgrounds, bmr6 and bmr6 bmr12 double mutant plants grown at Mead had significantly smaller mean lesion lengths than the corresponding wildtype (P ≤ 0.05). To assess responses of the two genetic backgrounds to controlled (greenhouse) water stress, wildtype RTx430 and Wheatland plants were inoculated with F. thapsinum under well‐watered and water stress conditions. Mean lesion lengths resulting on water deficit plants were significantly larger than those on well‐watered plants (P = 0.01). These results indicate that this bioassay can be used to screen sorghum lines in the greenhouse for increased resistance or tolerance to both drought and fusarium stalk rot.

Fermentation of undetoxified sugarcane bagasse hydrolyzates using a two stage hydrothermal and mechanical refining pretreatment

In this study, liquid hot water pretreatment was combined with disk milling for pretreatment of sugarcane bagasse. Sugarcane bagasse was pretreated using liquid hot water (LHW) at 140–180 °C for 10 min (20% w/w solids content) and then disk milled. Disk milling improved glucose release 41–177% and ethanol production from glucose/xylose cofermentation by 80% compared to only using LHW pretreatment. The highest ethanol conversion efficiency achieved was 94%, which was observed when bagasse was treated at 180 °C with LHW and disk milled. However, a small amount of residual xylose (3 g/L) was indicative that further improvement could be achieved to increase ethanol production.

Use of durum wheat clear flour in vital gluten and bioethanol production

During milling of durum wheat (Triticum durum) into semolina used for pasta processing, certain amount of clear flour (5–15%) with low economic value is obtained. This study aimed at determining the suitability of durum clear flours for vital gluten and bioethanol productions. The durum clear flours were wet-processed into vital gluten by three wet-milling methods, namely dough-washing, dough-water dispersion and flour-water dispersion. Vital glutens with acceptable purities (71.0–82.1% protein, Nx5.7, dm), yields (9.8–14.3%, dm) and recoveries (48.7–76.8%) were achieved by the dough-water and flour-water dispersion methods. However, vital gluten by the dough-washing method could not be isolated satisfactorily. The dough mixing and breadmaking qualities of vital glutens from the clear flours were found comparable to the commercial vital gluten. The carbohydrate-rich remnants of the clear flours upon isolation of glutens were subjected to enzymatic hydrolysis and yeast fermentation, leading to ethanol yields and conversion efficiencies of 32.2–33.5% (g/g, based on clear flour solids) and 80.5–87.6%, respectively. In conclusion, except for the dough-washing method, vital gluten and bioethanol with acceptable purities, yields, recoveries and qualities can be produced by the dough-water and flour-water dispersion methods.

Fermentation technology to improve productivity in dry grind corn process for bioethanol production

High solid fermentation during bioethanol production is a promising process engineering strategy to reduce total energy use and water requirements, and to improve productivity. However, ethanol toxicity at higher concentrations restricts the corn solids to 30–32% (w/w) during dry grind corn ethanol process. This work, using in situ ethanol removal, results in two big improvements in the fermentation process: 1) achieve complete fermentation of high solids slurries (up to 42%) at typical commercial enzyme dosages, and 2) fasten the fermentation process for currently used process with 32% solids. Application of vacuum at optimal times during fermentation (1 h at 12, 24, 36, and 48 h) of 40% corn solids resulted in complete fermentation, compared to about 12% residual glucose in the conventional process. The ethanol yield of 0.42 L/kg of dry corn with about 80% ethanol conversion efficiency was 88% higher than that of the conventional process at 42% solids (0.22 L/kg dry corn). Application of 1.5 h of vacuum at 18 and 24 h of fermentation with 32% solids resulted in high fermentation rates and decreased the fermentation time by more than 50%. Shorter fermentation times can allow processing of more material with the same equipment and allow smaller fermentation tanks in new plants, which would lead to both, lower capital and operating cost.

Combining sestc engineered A. niger with sestc engineered S. cerevisiae to produce rice straw ethanol via step-by-step and in situ saccharification and fermentation.

The development of agricultural residue ethanol has a profound effect on the environment protection and energy supply. To increase the production efficiency of straw ethanol and reduce operation progress, the single-enzyme-system-three-cellulase gene (sestc) engineered Aspergillus niger and sestc engineered Saccharomyces cerevisiae were combined to produce ethanol using the pretreated rice straw as the substrate. The present results showed that both the step-by-step and in situ saccharification and fermentation can effectively produce ethanol using rice straw as the carbon substrate. The conversion rates of ethanol were 12.76 and 14.56g per 1kg of treated rice straw, respectively, via step-by-step and in situ processes. In situ process has higher ethanol conversion efficiency of rice straw and fewer operation processes as compared with step-by-step process. Therefore, in situ saccharification and fermentation is a more economical and effective pathway to convert rice straw into ethanol. This study provides a reference to the conversion of lignocellulosic residues into ethanol with a combination of two kinds of sestc engineered strains.

Production of ethanol by thermophilic oligosaccharide utilising Geobacillus thermoglucosidasius TM242 using palm kernel cake as a renewable feedstock

Palm kernel cake (PKC) is a mannan rich by-product from palm oil processing with potential for conversion to fuels and chemicals in biorefineries. However, mannanase, the key enzyme required for the biodegradation of mannan tends to produce short chain mannose oligomers which need further conversion by mannosidases before the resulting monomers can be used by most ethanologens. In this study, Geobacillus thermoglucosidasius TM242, an engineered thermophilic ethanologen capable of utilising short-chain oligosaccharides was used for production of ethanol from a PKC hydrolysate rich in mannose oligomers without mannosidase supplementation, with high ethanol conversion efficiency. The highest amount of fermentable sugars of 28.34 ± 0.06 g/L was obtained from 5% (w/w) PKC pretreated by steam explosion at 4.5 bar for 15 min followed by enzymatic hydrolysis using 17.9 U/g mannan of SEB mannanase and 10.4 FPU/g glucan of CTec2 cellulase. Fermentation of the PKC hydrolysate by TM242 at 60 °C for 48 h gave a maximum ethanol concentration of 9.9 ± 0.4 g/L, equivalent to 92 ± 2% of the theoretical yield based on the total convertible sugars in PKC. This was considerably higher than that obtained using Saccharomyces cerevisiae (35.4%) using PKC hydrolysed under the same conditions or the autoclave treated PKC (P < 0.05). The process developed is attractive for ethanol production from mannan-rich wastes as it requires mild pretreatment conditions and avoids β-mannosidase supplementation in the hydrolysis step with utilization of all sugar types and oligosaccharides in the substrate.

Use of Pigmented Maize in Both Conventional Dry‐Grind and Modified Processes Using Granular Starch Hydrolyzing Enzyme

In the dry‐grind ethanol process, distillers dried grains with solubles (DDGS) is the main coproduct, which is primarily used as an ingredient in ruminant animal diets. Increasing the value of DDGS will improve the profitability of the dry‐grind ethanol process. One way to increase DDGS value is to use pigmented maize as the feedstock for ethanol production. Pigmented maize is rich in anthocyanin content, and the anthocyanin imparts red, blue, and purple color to the grain. It is reported that anthocyanin would be absorbed by yeast cell walls during the fermentation process. The effects of anthocyanin on fermentation characteristics in the dry‐grind process are not known. In this study, the effects of anthocyanin in conventional (conventional starch hydrolyzing enzymes) and modified (granular starch hydrolyzing enzymes [GSHE]) dry‐grind processes were evaluated. The modified process using GSHE replaced high‐temperature liquefaction. The ethanol conversion efficiencies of pigmented maize were comparable to that of yellow dent corn in both conventional (78.4 ± 0.5% for blue maize, 74.3 ± 0.4% for red maize, 81.2 ± 1.0% for purple maize, and 75.1 ± 0.2% for yellow dent corn) and modified dry‐grind processes using GSHE (83.8 ± 0.8% for blue maize, 81.1 ± 0.3% for red maize, 93.5 ± 0.8% for purple maize, and 85.6 ± 0.1% for yellow dent corn). Total anthocyanin content in DDGS from the modified process was 1.4, 1.9, and 2.4 times of that from the conventional process for purple, red, and blue maize samples, respectively. These results indicated that pigmented maize rich in anthocyanin did not negatively affect the fermentation characteristics of the dry‐grind process and that there was a potential to use pigmented maize in the dry‐grind process, especially when using GSHE.