Ethanol fermentation withKluyveromyces marxianusfrom Jerusalem artichoke grown in salina and irrigated with a mixture of seawater and freshwater

Functional characterisation of a new halotolerant seawater active glycoside hydrolase family 6 cellobiohydrolase from a salt marsh

Realising a fully circular bioeconomy requires the valorisation of lignocellulosic biomass. Cellulose is the most attractive component of lignocellulose but depolymerisation is inefficient, expensive and resource intensive requiring substantial volumes of potable water. Seawater is an attractive prospective replacement, however seawater tolerant enzymes are required for the development of seawater-based biorefineries. Here, we report a halophilic cellobiohydrolase SMECel6A, identified and isolated from a salt marsh meta-exo-proteome dataset with high sequence divergence to previously characterised cellobiohydrolases. SMECel6A contains a glycoside hydrolase family 6 (GH6) domain and a carbohydrate binding module family 2 (CBM2) domain. Characterisation of recombinant SMECel6A revealed SMECel6A to be active upon crystalline and amorphous cellulose. Mono- and oligosaccharide product profiles revealed cellobiose as the major hydrolysis product confirming SMECel6A as a cellobiohydrolase. We show SMECel6A to be halophilic with optimal activity achieved in 0.5X seawater displaying 80.6 ± 6.93% activity in 1 × seawater. Structural predictions revealed similarity to a characterised halophilic cellobiohydrolase despite sharing only 57% sequence identity. Sequential thermocycling revealed SMECel6A had the ability to partially reversibly denature exclusively in seawater retaining significant activity. Our study confirms that salt marsh ecosystems harbour enzymes with attractive traits with biotechnological potential for implementation in ionic solution based bioprocessing systems.

Biofuels from inulin-rich feedstocks: A comprehensive review

Biofuels are considered as a pre-eminent alternate to fossil fuels to meet the demand of future energy supply in a sustainable manner. Conventionally, they are produced from lignocellulosic raw materials. Saccharification of lignocellulosic raw materials for bioethanol production is a cumbersome process as compared to inulin-rich feedstocks. Various inulin-rich feedstocks, viz. jerusalem artichoke, chicory, dahlia, asparagus sp., etc. has also been exploited for the production of biofuels, viz. bioethanol, acetone, butanol, etc. The ubiquitous availability of inulin-rich feedstocks and presence of large amount of inulin makes them a robust substrate for biofuels production. Different strategies, viz. separate hydrolysis and fermentation, simultaneous saccharification and fermentation and consolidated bioprocessing have been explored for the conversion of inulin-rich feedstocks into biofuels. These bioprocess strategies are simple and efficient. The present review elaborates the prospective of inulin-rich feedstocks for biofuels production. Bioprocess strategies exploited for the conversion of inulin-rich feedstocks have also been highlighted.

Kluyveromyces marxianus: a potential biocatalyst of renewable chemicals and lignocellulosic ethanol production

Kluyveromyces marxianus is an ascomycetous yeast which has shown promising results in cellulosic ethanol and renewable chemicals production. It can survive on a variety of carbon sources under industrially favorable conditions due to its fast growth rate, thermotolerance, and acid tolerance. K. marxianus, is generally regarded as a safe (GRAS) microorganism, is widely recognized as a powerhouse for the production of heterologous proteins and is accepted by the US Food and Drug Administration (USFDA) for its pharmaceutical and food applications. Since lignocellulosic hydrolysates are comprised of diverse monomeric sugars, oligosaccharides and potential metabolism inhibiting compounds, this microorganism can play a pivotal role as it can grow on lignocellulosic hydrolysates coping with vegetal cell wall derived inhibitors. Furthermore, advancements in synthetic biology, for example CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats with Cas9)-mediated genome editing, will enable development of an engineered yeast for the production of biochemicals and biopharmaceuticals having a myriad of industrial applications. Genetic engineering companies such as Cargill, Ginkgo Bioworks, DuPont, Global Yeast, Genomatica, and several others are actively working to develop designer yeasts. Given the important traits and properties of K. marxianus, these companies may find it to be a suitable biocatalyst for renewable chemicals and fuel production on the large scale. This paper reviews the recent progress made with K. marxianus biotechnology for sustainable production of ethanol, and other products utilizing lignocellulosic sugars.

Developing a broad-range promoter set for metabolic engineering in the thermotolerant yeast Kluyveromyces marxianus

Kluyveromyces marxianus is an emerging host for metabolic engineering. This thermotolerant yeast is the fastest growing eukaryote, has high flux through the TCA cycle, and can metabolize a broad range of C5, C6, and C12 carbon sources. In comparison to the common host Saccharomyces cerevisiae, this non-conventional yeast suffers from a lack of metabolic engineering tools to control gene expression over a wide transcriptional range. To address this issue, we designed a library of 25 native-derived promoters from K. marxanius CBS6556 that spans 87-fold transcriptional strength under glucose metabolism. Six promoters from the library were further characterized in both glucose and xylose as well as across various temperatures from 30 to 45 ​°C. The temperature study revealed that in most cases EGFP expression decreased with elevating temperature; however, two promoters, P _SSA3 and P _ADH1 , increased expression above 40 ​°C in both xylose and glucose. The six-promoter set was also validated in xylose for triacetic acid lactone (TAL) production. By controlling the expression level of heterologous 2-pyrone synthase (2-PS), the specific TAL titer increased over 8-fold at 37 ​°C. Cultures at 41 ​°C exhibited a similar TAL biosynthesis capability, while at 30 ​°C TAL levels were lower. Taken together, these results advance the metabolic engineering tool set in K. marxianus and further develop this new host for chemical biosynthesis.

Impact of feedstocks and downstream processing technologies on the economics of caproic acid production in fermentation by Megasphaera elsdenii T81

Caproic acid (CA) was produced by Megasphaera elsdenii T81 with Jerusalem artichoke tubers (JA) as a feedstock. More CA was produced under the medium with the acid hydrolysate of JA than the comparative medium with a carbon composition similar to that of JA. CA was produced up to 13.0 g/L and 0.52 g/L/h with extractive fermentation using a mixed solvent of alamine 336 in oleyl alcohol at 37 °C. The JA cost to produce 1 ton of CA is only 505 USD, which is much lower than that required for purchasing sucrose (860 USD) in CA production. As a result of the analysis performed using SuperPro Designer, including the cost of distillation to obtain pure CA, the estimated production cost for CA from dry JA is 1869 USD/ton CA at the production scale of 2000 ton/year, which is lower than the current market price for petroleum-derived CA (~2500 USD/ton).

Biotechnological applications of inulin-rich feedstocks

Inulin is a naturally occurring second largest storage polysaccharide with a wide range of applications in pharmaceutical and food industries. It is a robust polysaccharide which consists of a linear chain of β-2, 1-linked-d-fructofuranose molecules terminated with α-d-glucose moiety at the reducing end. It is present in tubers, bulbs and tuberous roots of more than 36,000 plants belonging to both monocotyledonous and dicotyledonous families. Jerusalem artichoke, chicory, dahlia, asparagus, etc. are important inulin-rich plants. Inulin is a potent substrate and inducer for the production of inulinases. Inulin/inulin-rich feedstocks can be used for the production of fructooligosaccharides and high-fructose syrup. Additionally, inulin-rich feedstocks can also be exploited for the production of other industrially important products like acetone, butanol, bioethanol, single cell proteins, single cell oils, 2, 3-butanediol, sorbitol, mannitol, etc. Current review highlights the biotechnological potential of inulin-rich feedstocks for the production of various industrially important products.

The establishment of a marine focused biorefinery for bioethanol production using seawater and a novel marine yeast strain

Current technologies for bioethanol production rely on the use of freshwater for preparing the fermentation media and use yeasts of a terrestrial origin. Life cycle assessment has suggested that between 1,388 to 9,812 litres of freshwater are consumed for every litre of bioethanol produced. Hence, bioethanol is considered a product with a high-water footprint. This paper investigated the use of seawater-based media and a novel marine yeast strain ‘Saccharomyces cerevisiae AZ65’ to reduce the water footprint of bioethanol. Results revealed that S. cerevisiae AZ65 had a significantly higher osmotic tolerance when compared with the terrestrial reference strain. Using 15-L bioreactors, S. cerevisiae AZ65 produced 93.50 g/L ethanol with a yield of 83.33% (of the theoretical yield) and a maximum productivity of 2.49 g/L/h when using seawater-YPD media. This approach was successfully applied using an industrial fermentation substrate (sugarcane molasses). S. cerevisiae AZ65 produced 52.23 g/L ethanol using molasses media prepared in seawater with a yield of 73.80% (of the theoretical yield) and a maximum productivity of 1.43 g/L/h. These results demonstrated that seawater can substitute freshwater for bioethanol production without compromising production efficiency. Results also revealed that marine yeast is a potential candidate for use in the bioethanol industry especially when using seawater or high salt based fermentation media.

Recent advances in bio-based multi-products of agricultural Jerusalem artichoke resources

The Jerusalem artichoke is a perennial plant that belongs to the sunflower family. As a non-grain crop, Jerusalem artichoke possesses a number of desirable characteristics that make it a valuable feedstock for biorefinery, such as inulin content, rapid growth, strong adaptability, and high yields. This review provides a comprehensive introduction to renewable Jerusalem artichoke-based biomass resources and recent advances in bio-based product conversion. Furthermore, we discuss the latest in the development of inulinase-producing microorganisms and enhanced inulin hydrolysis capacity of microbes by genetic engineering, which lead to a more cost-effective Jerusalem artichoke biorefinery. The review is aimed at promoting Jerusalem artichoke industry and new prospects for higher value-added production.

Identification of hexose kinase genes in Kluyveromyces marxianus and thermo-tolerant one step producing glucose-free fructose strain construction

In yeast, the hexose assimilation is started at hexose phosphorylation. However, in Kluyveromyces marxianus, the hexokinase (HXK) and glucokinase (GLK) genes were not identified by experiments. Meanwhile, the glucose-free fructose product requires more cost-efficient method. In this study, the KmHXK1 and KmGLK1 genes were functionally identified through gene disruption, over-expression and recombinant enzymes characterization. Both glucose and fructose assimilation ability decreased significantly in KmHXK1 disrupted strain YLM001, however, this ability was not changed obviously in KmGLK1 disrupted strain YLM002. When over-expressing KmGLK1 in YLM001, only the glucose assimilation ability was recovered in obtained strain (YLM005). The kinetic constant analysis of recombinant enzymes also proved that KmHXK1 could phosphorylate glucose (Vmax 553.01 U/mg, Km 0.83 mM) and fructose (Vmax 609.82 U/mg, Km 0.52 mM), and KmGLK1 only phosphorylate glucose with a Vmax of 0.73 U/mg and a Km 4.09 mM. A thermo-tolerant strain YGR003 which produced glucose-free fructose from Jerusalem artichoke tuber in one step was constructed based on the obtained information. The highest production and fastest productivity were 234.44 g/L and 10.26 g/L/h, respectively, which were several folds of the results in previous reports.

Consolidated ethanol production from Jerusalem artichoke tubers at elevated temperature by Saccharomyces cerevisiae engineered with inulinase expression through cell surface display

Ethanol fermentation from Jerusalem artichoke tubers was performed at elevated temperatures by the consolidated bioprocessing strategy using Saccharomyces cerevisiae MK01 expressing inulinase through cell surface display. No significant difference was observed in yeast growth when temperature was controlled at 38 and 40 °C, respectively, but inulinase activity with yeast cells was substantially enhanced at 40 °C. As a result, enzymatic hydrolysis of inulin was facilitated and ethanol production was improved with 89.3 g/L ethanol produced within 72 h from 198.2 g/L total inulin sugars consumed. Similar results were also observed in ethanol production from Jerusalem artichoke tubers with 85.2 g/L ethanol produced within 72 h from 185.7 g/L total sugars consumed. On the other hand, capital investment on cooling facilities and energy consumption for running the facilities would be saved, since regular cooling water instead of chill water could be used to cool down the fermentation system.

Growth, ethanol production, and inulinase activity on various inulin substrates by mutant Kluyveromyces marxianus strains NRRL Y-50798 and NRRL Y-50799

Economically important plants contain large amounts of inulin. Disposal of waste resulting from their processing presents environmental issues. Finding microorganisms capable of converting inulin waste to biofuel and valuable co-products at the processing site would have significant economic and environmental impact. We evaluated the ability of two mutant strains of Kluyveromyces marxianus (Km7 and Km8) to utilize inulin for ethanol production. In glucose medium, both strains consumed all glucose and produced 0.40 g ethanol/g glucose at 24 h. In inulin medium, Km7 exhibited maximum colony forming units (CFU)/mL and produced 0.35 g ethanol/g inulin at 24 h, while Km8 showed maximum CFU/mL and produced 0.02 g ethanol/g inulin at 96 h. At 24 h in inulin + glucose medium, Km7 produced 0.40 g ethanol/g (inulin + glucose) and Km8 produced 0.20 g ethanol/g (inulin + glucose) with maximum CFU/mL for Km8 at 72 h, 40 % of that for Km7 at 36 h. Extracellular inulinase activity at 6 h for both Km7 and Km8 was 3.7 International Units (IU)/mL.

Enhancing inulinase yield by irradiation mutation associated with optimization of culture conditions

A new inulinase-producing strain was isolated from rhizosphere soils of Jerusalem artichoke collected from Shihezi (Xinjiang, China) using Jerusalem artichoke power (JAP) as sole carbon source. It was identified as an Aspergillus niger strain by analysis of 16S rRNA. To improve inulinase production, this fungus was subjected to mutagenesis induced by ⁶⁰Co γ-irradiation. A genetically stable mutant (designated E12) was obtained and it showed 2.7-fold higher inulinase activity (128 U/mL) than the parental strain in the supernatant of a submerged culture. Sequential methodology was used to optimize the inulinase production of stain E12. A screening trial was first performed using Plackett-Burman design and variables with statistically significant effects on inulinase bio-production were identified. These significant factors were further optimized by central composite design experiments and response surface methodology. Finally, it was found that the maximum inulinase production (185 U/mL) could be achieved under the optimized conditions namely pH 7.0, yeast extract concentration of 5.0 g/L, JAP concentration of 66.5 g/L, peptone concentration of 29.1 g/L, solution volume of 49.4 mL in 250-mL shake flasks, agitation speed of 180 rpm, and fermentation time of 60 h. The yield of inulinase under optimized culture conditions was approximately 1.4-fold of that obtained by using basal culture medium. These findings are of significance for the potential industrial application of the mutant E12.

Invertase Suc2-mediated inulin catabolism is regulated at the transcript level in Saccharomyces cerevisiae

Background

Invertase Suc2 was recently identified as a key hydrolase for inulin catabolism in Saccharomyces cerevisiae, whereas the Suc2 activity degrading inulin varies greatly in different S. cerevisiae strains. The molecular mechanism causing such variation remained obscure. The aim of this study is to investigate how Suc2 activity is regulated in S. cerevisiae.

Results

The effect of SUC2 expression level on inulin hydrolysis was investigated by introducing different SUC2 genes or their corresponding promoters in S. cerevisiae strain BY4741 that can only weakly catabolize inulin. Both inulinase and invertase activities were increased with the rising SUC2 expression level. Variation in the promoter sequence has an obvious effect on the transcript level of the SUC2 gene. It was also found that the high expression level of SUC2 was beneficial to inulin degradation and ethanol yield.

Conclusions

Suc2-mediated inulin catabolism is regulated at transcript level in S. cerevisiae. Our work should be valuable for engineering advanced yeast strains in application of inulin for ethanol production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0243-3) contains supplementary material, which is available to authorized users.

The prospects of Jerusalem artichoke in functional food ingredients and bioenergy production

Jerusalem artichoke, a native plant to North America has recently been recognized as a promising biomass for bioeconomy development, with a number of advantages over conventional crops such as low input cultivation, high crop yield, wide adaptation to climatic and soil conditions and strong resistance to pests and plant diseases. A variety of bioproducts can be derived from Jerusalem artichoke, including inulin, fructose, natural fungicides, antioxidant and bioethanol. This paper provides an overview of the cultivation of Jerusalem artichoke, derivation of bioproducts and applicable production technologies, with an expectation to draw more attention on this valuable crop for its applications as biofuel, functional food and bioactive ingredient sources.

Transcriptional analysis of Kluyveromyces marxianus for ethanol production from inulin using consolidated bioprocessing technology

BACKGROUND

Ethanol production from non-crop materials, such as Jerusalem artichokes, would make a great contribution to the energy industry. The non-conventional yeast, Kluyveromyces marxianus, is able to carry out ethanol fermentation of sugar molecules obtained from inulin-containing materials by consolidated bioprocessing. Lower inulin concentrations and micro-aeration can lead to a relatively fast and ideal fermentation process; however, it is unclear what causes the inhibition of higher concentrations of inulin and the promotion effect of aeration.

RESULTS

Next-generation sequencing technology was used to study the global transcriptional response of K. marxianus Y179 under three fermentation conditions, including 120 g/L inulin without aeration (120-N), 230 g/L inulin without aeration (230-N), 230 g/L inulin with aeration by ORP controlling at -130 mV (230-130mV). A total of 35.55 million clean reads were generated from three samples, of which 4,820 predicted that open reading frames were annotated. For differential expression analysis, 950 and 1,452 differentially expressed genes were discovered under the conditions of 230-130mV and 120-N, respectively, and the sample 230-N was used as the control. These genes are mainly associated with the pathways of central carbon metabolism and ethanol formation. Increased expression of inulinase and the low activity of the autophagy-related gene, ATG8, ensured fast and ideal fermentation processes.

CONCLUSIONS

Despite being reported as the "crabtree-negative" species, K. marxianus Y179 could achieve favorable ethanol fermentation profiles under micro-aeration and high inulin concentrations. K. marxianus Y179 cells responded to inulin concentrations and micro-aeration that is involved in the whole ethanol metabolism network. These results will serve as an important foundation for further exploration of the regulatory mechanisms involved in ethanol fermentation from inulin by consolidated bioprocessing and also provide a valuable reference for future studies on optimization and reconstruction of the metabolism network in K. marxianus.

Ethanol production using a newly isolated Saccharomyces cerevisiae strain directly assimilating intact inulin with a high degree of polymerization

An inulin-degrading strain L610, which was competent to directly convert inulin into ethanol, was isolated and identified as a strain of Saccharomyces cerevisiae according to physiological and phylogenetic analysis. Ion chromatography results showed that isolate L610 could assimilate the intact inulin completely without acidic or enzymatic pretreatment in contrast to the previously reported strains of S. cerevisiae, which could only ferment the fructo-oligosaccharides with a degree of polymerization less than 15. Strain L610 yielded 37.2 g/L ethanol within 48 H at a shake flask level under the evaluated culture conditions (11% inulin, 0.4% yeast extract, and 0.05% MgSO4 at 30 °C and pH 6.0). The conversion efficiency of inulin-type sugar to ethanol was 60% of the theoretical ethanol yield. Strain L610 produced 40.0 g/L of ethanol when directly fermented in Jerusalem artichoke (Helianthus tuberosus L.) powder suspension within 24 H, which was higher than the reported data, 28.9 g/L, produced by S. cerevisiae KCCM 50549.

Identification of a xylitol dehydrogenase gene from Kluyveromyces marxianus NBRC1777

Xylitol dehydrogenase (XDH) (EC 1.1.1.9) is one of the key enzymes in the xylose fermentation pathway in yeast and fungi. A xylitol dehydrogenase gene (XYL2) encoding a XDH was cloned from Kluyveromyces marxianus NBRC 1777, and the in vivo function was validated by disruption and complementation analysis. The highest activity of KmXDH could be observed at pH 9.5 during 55°C. The values of k(cat)/K(m) indicate that KmXDH prefers NAD(+) to NADP(+) (k(cat)/K(m NAD)(+) 3681/min mM and k(cat)/K(m NADP)(+) 1361/min mM). The different coenzyme preference between KmXR and KmXDH caused an accumulation of NADH in the xylose utilization pathway. The redox imbalance may be one of the reasons to cause the poor xylose fermentation under oxygen-limited conditions in K. marxianus NBRC1777.

Consolidated bioprocessing of highly concentrated Jerusalem artichoke tubers for simultaneous saccharification and ethanol fermentation

Consolidated bioprocessing (CBP) of Jerusalem artichoke tuber (Jat) for ethanol production is one of the most promising options for an alternate biofuel technology development. The technical barriers include the weak saccharolytic enzyme (inulinase) activity of the fermentation strain, and the well mixing of the high viscous fermentation slurry at the highly concentrated Jat loading. In this study, Saccharomyces cerevisiae DQ1 was found to produce relatively large amount of inulinase for hydrolysis of inulin in Jat, and the helical ribbon stirring bioreactor used provided well mixing performance under the high Jat loading. Even a highly concentrated Jat loading up to 35% (w/w) in the helical ribbon bioreactor for CBP was allowed. The results obtained from this study have demonstrated a feasibility of developing a CBP process technology in the helical ribbon bioreactor for ethanol production at a high yield 128.7 g/L and the theoretical yield 73.5%, respectively. This level of ethanol yield from Jat is relatively higher than others reported so far. The results of this study could provide a practical CBP process technology in the helical ribbon bioreactor for economically sustainable alternate biofuel production using highly concentrated inulin containing biomass feedstock such as Jat, at least 35%.

Thermotolerant Kluyveromyces marxianus and Saccharomyces cerevisiae strains representing potentials for bioethanol production from Jerusalem artichoke by consolidated bioprocessing

Thermotolerant inulin-utilizing yeast strains are desirable for ethanol production from Jerusalem artichoke tubers by consolidated bioprocessing (CBP). To obtain such strains, 21 naturally occurring yeast strains isolated by using an enrichment method and 65 previously isolated Saccharomyces cerevisiae strains were investigated in inulin utilization, extracellular inulinase activity, and ethanol fermentation from inulin and Jerusalem artichoke tuber flour at 40 °C. The strains Kluyveromyces marxianus PT-1 (CGMCC AS2.4515) and S. cerevisiae JZ1C (CGMCC AS2.3878) presented the highest extracellular inulinase activity and ethanol yield in this study. The highest ethanol concentration in Jerusalem artichoke tuber flour fermentation (200 g L(-1)) at 40 °C achieved by K. marxianus PT-1 and S. cerevisiae JZ1C was 73.6 and 65.2 g L(-1), which corresponded to the theoretical ethanol yield of 90.0 and 79.7 %, respectively. In the range of 30 to 40 °C, temperature did not have a significant effect on ethanol production for both strains. This study displayed the distinctive superiority of K. marxianus PT-1 and S. cerevisiae JZ1C in the thermotolerance and utilization of inulin-type oligosaccharides reserved in Jerusalem artichoke tubers. It is proposed that both K. marxianus and S. cerevisiae have considerable potential in ethanol production from Jerusalem artichoke tubers by a high temperature CBP.

Consolidated bioprocessing strategy for ethanol production from Jerusalem artichoke tubers by Kluyveromyces marxianus under high gravity conditions

AIMS

Developing an innovative process for ethanol fermentation from Jerusalem artichoke tubers under very high gravity (VHG) conditions.

METHODS AND RESULTS

A consolidated bioprocessing (CBP) strategy that integrated inulinase production, saccharification of inulin contained in Jerusalem artichoke tubers and ethanol production from sugars released from inulin by the enzyme was developed with the inulinase-producing yeast Kluyveromyces marxianus Y179 and fed-batch operation. The impact of inoculum age, aeration, the supplementation of pectinase and nutrients on the ethanol fermentation performance of the CBP system was studied. Although inulinase activities increased with the extension of the seed incubation time, its contribution to ethanol production was negligible because vigorously growing yeast cells harvested earlier carried out ethanol fermentation more efficiently. Thus, the overnight incubation that has been practised in ethanol production from starch-based feedstocks is recommended. Aeration facilitated the fermentation process, but compromised ethanol yield because of the negative Crabtree effect of the species, and increases the risk of contamination under industrial conditions. Therefore, nonaeration conditions are preferred for the CBP system. Pectinase supplementation reduced viscosity of the fermentation broth and improved ethanol production performance, particularly under high gravity conditions, but the enzyme cost should be carefully balanced. Medium optimization was performed, and ethanol concentration as high as 94·2 g l(-1) was achieved when 0·15 g l(-1) K(2) HPO(4) was supplemented, which presents a significant progress in ethanol production from Jerusalem artichoke tubers.

CONCLUSIONS

A CBP system using K. marxianus is suitable for efficient ethanol production from Jerusalem artichoke tubers under VHG conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Jerusalem artichoke tubers are an alternative to grain-based feedstocks for ethanol production. The high ethanol concentration achieved using K. marxianus with the CBP system not only saves energy consumption for ethanol distillation, but also significantly reduces the amount of waste distillage discharged from the distillation system.

Ethanol fermentation from Jerusalem artichoke powder using Saccharomyces cerevisiae KCCM50549 without pretreatment for inulin hydrolysis

A strain of Saccharomyces cerevisiae, KCCM50549, was found to efficiently ferment the inulin-containing carbohydrates in Jerusalem artichoke without acidic or enzymatic pretreatment prior to fermentation. S. cerevisiae KCCM50549 could utilize almost completely the fructo-oligosaccharides present in Jerusalem artichoke (up to degree of polymerization (DP) of 15), in contrast to the other S. cerevisiae strain such as NCYC625 that fermented the fructo-oligosaccharides with DP of up to around six. Inulin-fermenting S. cerevisiae KCCM50549 produced c.a. 1.6 times more ethanol from Jerusalem artichoke compared with S. cerevisiae NCYC625. Direct ethanol fermentation of Jerusalem artichoke flour at 180 g/L without any supplements or pretreatments by S. cerevisiae KCCM50549 in a 5 L jar fermentor yielded 36.2 g/L of ethanol within 36 h. The conversion efficiency of inulin-type sugars to ethanol was 70% of the theoretical ethanol yield.