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Effective enzymatic hydrolysis of lignocellulosic materials to produce fermentable sugars requires close cooperation between cellulase components. However, lignin remaining in the pre-treated substrate plays an inhibitory role in the synergistic action of enzymes through irreversible adsorption. In this study, the effect of cellulolytic enzyme lignin (CEL) isolated from pre-treated furfural residues and dissolved lignins (DLs) precipitated from black liquor on cellulase and cellobiase adsorption behavior was investigated. Green liquor (GL) combined with H2O2 (GL-H2O2) or ethanol (GL-ethanol) pre-treatments markedly decreased the adsorption capacity of CELs. However, the DLs had the strongest binding ability, which was approximately two to three times higher than that of CELs. According to SDS–PAGE analyses, only CBHII and EGII in cellulase and enzymes of 245 kDa and 55 kDa molecular weight in cellobiase were easily bound onto CELs and DLs. Solid-state 13C NMR spectra and FT-IR analysis indicated that pre-treatments reduced the hydrophobic structure of aromatic rings, β-O-4, and carbonyl, and increased the number of hydrophilic carboxyl groups in CELs. For this reason, the hydrophobicity of CELs was decreased, thus reducing their adsorption capacity. Compared with GL-H2O2 pre-treatment, GL-ethanol pre-treatment had a stronger effect on decreasing enzyme adsorption of lignin due to its high hydrophilicity. Heavy damage to aromatic structures, low molecular weight, and the large number of aliphatic portions in DLs caused their strong affinity for enzymes, although their BET surface area and hydrophobicity were low.

Camellia oleifera shell (COS), a by-product of processing woody vegetable oil, is rich in hemicellulose and lignin. In this study, we investigated the effects of acid concentration, pretreatment temperature and reaction time on the concentration and yield of xylo-oligosaccharides (XOS) and the degree of polymerization (DP) distribution of XOS when pretreating COS with malic acid (MA). Under moderate condition (2 M MA, 120 ℃, 30 min), the maximum yield of XOS with DP 2–4 was 48.78% (based on the initial xylan) with low xylose, 5-hydroxymethylfurfural (HMF) and furfural, in which xylobiose (X2), xylotriose (X3) and xylotraose (X4) concentrations were 5.22 g/L, 2.75 g/L and 2.91 g/L, respectively. In addition, acid-insoluble lignin (AIL) in the residue after MA pretreatment and milling wood lignin (MWL) were mainly composed of guaiacyl and syringyl. AIL has higher thermal stability than MWL, which can be the stabilizer for producing flame-resistant materials.

Co-production of glucose, furfural and other green materials based on a lignocellulosic biorefinery is a promising way to realize the commercial application of corncob residues. An effective process was developed for glucose production using low temperature bisulfite pretreatment and high-solids enzymatic hydrolysis. Corncob residues from furfural production (FRs) were pretreated with 0.1g NaHSO3/g dry substrate at 100°C for 3h. Lignin was sulfonated and sulfonic groups were produced during pretreatment, which resulted in decreasing the zeta potential of the samples. Compared with raw material, bisulfite pretreatment of FRs increased the glucose yield from 18.6 to 99.45% after 72h hydrolysis at a solids loading of 12.5%. The hydrolysis residues showed a relatively high thermal stability and concentrated high derivatives. Direct pretreatment followed by enzymatic hydrolysis is an environmentally-friendly and economically-feasible method for the production of glucose and high-purity lignin, which could be further converted into high-value products.

Gleditsia saponin (GS) assisted high-solids enzymatic hydrolysis and fermentation for alkaline peroxide (AP)-pretreated furfural residues (FRs) was investigated. The addition of GS increased the glucose yield of untreated FRs to 74.8% in high-solids-loading enzymatic hydrolysis. AP pretreatment before enzymatic hydrolysis resulted in a high sugar concentration (115.4 g/L) and a glucose yield of 57.5% by the end of hydrolysis at 20% solids loading. It was suggested that GS could improve significantly the glucose yields of FRs with high lignin content. After simultaneous saccharification and fermentation (SSF), the total cellulose conversion of FRs with 14.3% lignin content reached 82.2% and the highest ethanol concentration (69.1 g/L) was achieved, which was 121% higher than that of untreated FRs (30.1 g/L). The results indicated that the main reason behind the decreased glucose yield at high-solids loadings was product inhibition. Moreover, the lignin content plays an important role in the enhancement of GS-assisted high-solids enzymatic hydrolysis of AP-treated FRs.

Furfural residues (FRs) is an industrial waste material with an enormous potential for bio-ethanol production. In this study, FRs were pretreated with green liquor (GL) combined with hydrogen peroxide (GL–H2O2) or ethanol (GL-ethanol). The wettability and electrostatic contributions of untreated and pretreated FRs was investigated as well as that of isolated lignin cellulolytic enzyme lignin (CEL) and cellulose. The results showed that the hydrophilicity of FRs was increased after GL–H2O2 and GL-ethanol pretreatment. Lignin is the key factor that affects the hydrophilicity of substrate. The cellulase binding for lignin was reduced due to the increase of hydrophilicity of lignin, resulting in the improvement of enzymatic hydrolysis. The electrostatic contributions was also an important factor that influenced the cellulase binding of lignin. After pretreatments, the negative charge of lignin was decreased. Accordingly, the cellulase binding capacity was reduced. This effect was more significant after the GL-ethanol pretreatment. Thus, the glucose yield of the substrate obtained from the GL-ethanol pretreatment (86.1 %) was larger than that from the GL–H2O2 pretreatment (82.2 %). Unlike the CEL, GL–H2O2 pretreatment increased the negative charge of cellulose. And the increase of negative charge improved the affinity of cellulose to cellulase via electrostatic attraction. The XPS analyses indicated that the carbonyl groups from lignin play an important role in decreasing the hydrophobicity of the substrates.

Surfactants are popular additives for the prevention of the inhibitory effect of lignin on cellulolytic enzymes. Saponin is a type of natural surfactant extracted from Gleditsia spp. In this study, the effect of saponin on the high-solids-loading enzymatic hydrolysis of furfural residues (FRs) with a lignin content of 45% was investigated. The optimal dosage of Gleditsia saponin (GS) was determined to be 25-fold greater than its critical micelle concentration (CMC; 0.16 g/L). The addition of GS increased the cellulose conversion by up to 52.63% in high-solids-loading enzymatic hydrolysis. Due to the addition of GS, a maximum cellulose conversion of 74.88% was achieved after FRs had hydrolyzed for 120 h at a solids loading of 20% (w/w) with 30 filter paper unit (FPU)/g-cellulose. The decrease in cellulose conversion was found to exhibit a linear correlation with an increase in the solids loadings from 20.0% to 27.5% (w/w). The surface structural variations of hydrolytic residues were characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the carbonyl groups of lignin facilitated the binding of GS to the surface of lignin, which resulted in a decrease in the adsorption of between the enzyme and lignin. Interestingly, GS could maintain enzymatic activity in the supernatants.

Furfural residues (FRs) were pretreated with ethanol and a green liquor (GL) catalyst to produce fermentable sugar. Anthraquinone (AQ) was used as an auxiliary reagent to improve delignification and reduce cellulose decomposition. The results showed that 42.7% of lignin was removed and 96.5% of cellulose was recovered from substrates pretreated with 1.0 mL GL/g of dry substrate and 0.4% (w/w) AQ at 140 °C for 1 h. Compared with raw material, ethanol–GL pretreatment of FRs increased the glucose yield from 69.0% to 85.9% after 96 h hydrolysis with 18 FPU/g-cellulose for cellulase, 27 CBU/g-cellulose for β-glucosidase. The Brauner–Emmett–Teller surface area was reduced during pretreatment, which did not inhibit the enzymatic hydrolysis. Owing to the reduced surface area, the unproductive binding of cellulase to lignin was decreased, thus improving the enzymatic hydrolysis. The degree of polymerization of cellulose from FRs was too low to be a key factor for improving enzymatic hydrolysis.

A potential commercial pretreatment for furfural residues (FRs) was investigated by using a combination of green liquor and hydrogen peroxide (GL–H 2 O 2 ). The results showed that 56.2% of lignin removal was achieved when the sample was treated with 0.6 g H 2 O 2 /g-DS (dry substrate) and 6 mL GL/g-DS at 80 °C for 3 h. After 96 h hydrolysis with 18 FPU/g-cellulose for cellulase, 27 CBU/g-cellulose for β-glucosidase, the glucose yield increased from 71.2% to 83.6%. Ethylenediaminetetraacetic acid was used to reduce the degradation of H 2 O 2 , the glucose yield increased to 90.4% after the addition of 1% (w/w). The untreated FRs could bind more easily to cellulase than pretreated FRs could. The structural changes on the surface of sample were characterized by X-ray photoelectron spectroscopy. The results indicated that the surface lignin could be effectively removed during pretreatment, thereby decreasing the enzyme–lignin binding activity. Moreover, the carbonyl from lignin plays an important role in cellulase binding.

In this study, Streptococcus thermophilus and Lactobacillus bulgaricus were used to produce l(+)-lactic acid by simultaneous saccharification and fermentation (SSF). The use of hydrolyzed yeast as cheap nutrients and mixtures of cellulosic materials and starchy materials as carbon source for l(+)-LA production was evaluated. Heat treatment (121 °C) was proven to be an effective method to improve the performances of yeast as nutrients for the fermentations using different carbon sources. The addition of yeast hydrolyzate obviously lowered the surface tension of medium and improved enzyme hydrolysis of furfural residue (FR) as the concentration was beyond 10 g/L. Carbon–nitrogen ratio, substrates composition, substrates feeding rate and enzyme-feeding strategy will affect the productivity of l(+)-LA production from mixed substrates. SSF of FR and corn saccharification liquid tends to obtain good yields, when the total WIS content is in 10 % and carbon–nitrogen ratio is about 30. This study provides an encouraging means of producing l(+)-LA from lignocellulosic resource and starchy resource, which could optimize the use of raw materials.

Furfural residues produced from the furfural industry were investigated as a substrate for lactic acid production by simultaneous saccharification and fermentation (SSF). Alkaline peroxide was used for delignification of furfural residues to improve the final lactic acid concentration. The residue was treated with 1.3% to 1.7% hydrogen peroxide at 80 °C for 1 h with a substrate concentration of 3.33%. SSF of furfural residues with different delignification degrees were carried out to evaluate the effect of delignification degree on lactic acid production. Using corn hydrolysates/ furfural residues as substrates, SSF with different media were carried out to investigate the effect of lignin on the interaction between enzymes and lactic acid bacteria. Lactic acid bacteria had a negative effect on cellulase, thus resulting in the reduction of enzyme activity. Lignin and nutrients slowed down the decreasing trend of enzyme activity. A higher delignification resulted in a slower fermentation rate and lower yield due to degradation products of lignin and the effect of lignin on the interaction between enzymes and lactic acid bacteria. For the purpose of lactic acid production, a moderate delignification (furfural residues with the lignin content of 14.8%) was optimum.

The price of raw material, energy demand in the pretreatment step, and enzyme usage rate are the major cost factors in the process of converting biomass to bioethanol. Unwashed furfural residues (FRs) possess great potential for application in bioethanol production. Surfactant addition is an effective method to enhance the fermentation rate. In this study, unwashed FRs were used directly as raw materials to produce bioethanol. Tea-seed cake (TSC), tea seed residues that contained protein and saponin, was added in the simultaneous saccharification and fermentation (SSF) process. The effect of TSC dosage on SSF was compared. TSC was added at the dosage of 10 g/L, which resulted in a final ethanol yield of 87.2%. However, a high concentration of TSC could induce cytotoxicity in yeast. The surface tension (approximately 33.92 mM/m) at SSF using TSC-medium was much lower than that of other fermentation systems (about 64.67 mN/m). Further contact angle testing showed that TSC-medium (21.7°) had better wetting capacity than FRs (45.6°). This study provided a proposed process strategy that SSF with the addition of TSC could be a minimum consumption of chemicals and enzymes for future cellulosic ethanol production process.

Furfural residues, lignocellulosic residues from commercial furfural production, generally consist of cellulose, lignin, and a rather low amount of residual hemicellulose. They represent the most promising potential sources of biomass that are cheap and readily available in large quantities. Furfural residues with cellulose contents of 51.92%, 68.49%, 83.88%, and 94.92% were hydrolysed by a mixture of cellulase and β-glucosidase with an enzyme loading rate of 7.5 filter paper units/g and 15 cellobiase units/g of cellulose, respectively. We evaluated the filter paper activities of the digested furfural residues containing various cellulose concentrations. Both adsorption and desorption of the cellulase mixture to the lignocellulosic substrate were compared according to the filter paper activities of the digests. The higher the cellulose content of the lignocellulosic substrate, the higher was the apparent adsorption and desorption of the cellulase mixture; this indicates considerable adsorption between the enzyme and the lignin in the furfural residues. The glucose yield of furfural residues increased incrementally according to the cellulose content of the substrate. The highest glucose yield was obtained from the enzymatic hydrolysate of the furfural residue with a cellulose content of 94.92% after a 72-h saccharification. Furfural residues can be easily hydrolysed to fermentable sugars with mixtures of cellulase and β-glucosidase. Therefore, furfural residues are potential biomass resources for cellulosic ethanol production. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

Furfural residues are by-products from the process of furfural production with corncobs. The cellulose in the residues can be used to produce ethanol, but lignin, the other main component in the residues, inevitably exerts unfavourable effects on the enzymatic hydrolysis process. In order to reveal the effects and make an efficient utilization of the lignin, the characteristics, especially the variation during furfural production, should first be investigated. In this paper, the milled wood lignin (MWL) of the furfural residual (FR) and corncob were separated and a comparative study of the MWL fractions was made in terms of the UV, FT-IR, 1 H and 13 C NMR spectra as well as the molecular weight and the thermal stability. It was found that the proportion of the three structure units in the two kinds of lignin fractions was different and that some reactions had taken place on the benzene rings during furfural manufacture. The methoxyls in the lignin structure units had been removed partially, and the groups conjugated with the benzene rings were destroyed. Moreover, the alcoholichydroxyl in the lignin of the corncob reduced and transformed into carbonyl. Both the degradation of the lignin and the condensation reactions have emerged during the furfural production.

The enzymatic saccharification of pretreated furfural residues with different lignin content was studied to verify the effect of lignin removal in the hydrolysis process. The results showed that the glucose yield was improved by increasing the lignin removal. A maximum glucose yield of 96.8% was obtained when the residue with a lignin removal of 51.4% was hydrolyzed for 108 h at an enzyme loading of 25 FPU/g cellulose. However, further lignin removal did not increase the hydrolysis. The effect of enzyme loading on the enzymatic hydrolysis was also explored in this work. It was concluded that a high glucose yield of 90% was achieved when the enzyme dosage was reduced from 25 to 15 FPU/g cellulose, which was cost-effective for the sugar and ethanol production. The structures of raw material and delignified samples were further characterized by XRD and scanning electron microscopy (SEM).

This study reports four schemes to pretreat wet furfural residues (FRs) with sodium bisulfite for production of fermentable sugar. The results showed that non-detoxified FRs (pH 2-3) had great potential to lower the cost of bioconversion. The optimal process was that unwashed FRs were first pretreated with bisulfite, and the whole slurry was then directly used for enzymatic hydrolysis. A maximum glucose yield of 99.4% was achieved from substrates pretreated with 0.1 g NaHSO3/g dry substrate (DS), at a relatively low temperature of 100 °C for 3 h. Compared with raw material, enzymatic hydrolysis at a high-solid of 16.5% (w/w) specifically showed more excellent performance with bisulfite treated FRs. Direct bisulfite pretreatment improved the accessibility of substrates and the total glucose recovery. Lignosulfonate in the non-detoxified slurry decreased the non-productive adsorption of cellulase on the substrate, thus improving enzymatic hydrolysis.

Simultaneous saccharification and fermentation (SSF) is an attractive process configuration for bio-ethanol production. Further reductions in process cost of SSF are expected with the use of waste agricultural or industrial materials as feedstock. In the current study, two industrial lignocellulosic wastes, cassava residues (CR) and furfural residues (FR), were combined during SSF for ethanol production due to their value-added applications and positive environmental impacts. After CR were liquefied and saccharified, saccharification liquid was added to SSF of FR. The effect of substrate fractions was investigated in terms of ethanol yield, byproduct concentration and the number of yeast cells. Besides, a natural surfactant, Gleditsia saponin, was added to investigate the effect of FR lignin on SSF with 20% substrate concentration. The results showed that increasing the ratio of CR/FR improved the ethanol yield and that the ethanol yield was also increased gradually by increasing the substrate concentration from 6% to 12%. A high ethanol concentration of 36.0 g/L was obtained under the condition of CR:FR = 2:1 with 12% substrate concentration, reaching 71.1% of the theoretical yield. However, Gleditsia saponin did not affect the ethanol yield, indicating the insignificant effect of lignin in SSF with low lignin content in the reaction system.

Furfural residue (FR) is a waste lignocellulosic material with enormous potential for bioethanol production. In this study, bioethanol production from FR after delignification was compared. Hydrophilic variation was measured by conductometric titration to detect the relationship between hydrophilicity and bioethanol production. It was found that ethanol yield increased as delignification enhanced, and it reached up to 75.6% of theoretical yield for samples with 8.7% lignin. The amount of by-products decreased as delignification increased. New inflection points appeared in conductometric titration curves of samples that were partially delignified, but they vanished in the curves of the highly delignified samples. Total charges and carboxyl levels increased after slight delignification, and they decreased upon further delignification. These phenomena suggested some new hydrophilic groups were formed during pretreated delignification, which would be beneficial to enzymatic hydrolysis. However, some newly formed groups may act as toxicant to the yeast during simultaneous saccharification and fermentation.

Furfural residues (FRs) were pretreated with laccase or a laccase-mediator (1-hydroxybenzotriazole, HBT) system to produce fermentable sugar for bioethanol production. Compared to laccase-only pretreatment, laccase-mediator pretreatment dissolved more lignin. Approximately 10.5% of the initially present lignin was removed when FRs were treated with a laccase loading of 100 U/g of dry substrate in 1% (w/w) HBT at 48 °C for 24 h in an acetate buffer (pH 4.8). The enzymatic saccharification process was carried out by a combined laccase or laccase-mediator pretreatment without washing of the treated solids. The results showed that active laccase had a negative effect on the rate and yield of enzymatic hydrolysis. Laccase-oxidized HBT seriously reduced glucose yield. However, non-oxidized HBT increased glucose yield when laccase was deactivated at 121 °C for 20 min prior to enzymatic hydrolysis. The highest glucose yield, 80.9%, was obtained from the substrate pretreated with 100 U/g of dry substrate laccase and 1% (w/w) HBT at 48 °C for 24 h in an acetate buffer (pH 4.8). Furthermore, the structures of FRs before and after laccase-mediator pretreatment were characterized by scanning electron microscopy (SEM) and Fourier Transform Infrared spectroscopy (FT-IR).

Background Recently, interest in the utilization of corncob residue (CCR, with high lignin of 45.1%) as a feedstock for bioethanol has been growing. Surfactants have been one of the most popular additives intended to prevent the inhibitory effect of lignin on cellulolytic enzymes, thereby improving hydrolysis. In this study, the effects of biosurfactant tea saponin (TS) on the enzymatic hydrolysis of CCR and the bonding behavior of cellulolytic enzymes to the substrate were investigated. The surface tension in the supernatant was also detected to obtain information about the characteristics and stability of TS. Results The glucose concentration was 17.15 mg/mL at 120 hours of hydrolysis with the low loading of cellulolytic enzymes (7.0 FPU/g cellulose and 10.5 BGU/g cellulose) and 5% CCR. The optimal dosage of TS was its critical micelle concentration (cmc, 1.80 mg/mL). The glucose yield was enhanced from 34.29 to 46.28 g/100 g dry matter by TS. The results indicate that TS can promote the adsorption of cellulolytic enzymes on the substrate and mediate the release of adsorbed enzymes. Meanwhile, TS improves the recovery of the cellulolytic enzymes after a hydrolysis cycle and prevents deactivation of the enzymes during the intense shaking process. The surface tension in supernatants of digested CCR with TS remained at 50.00 mN/m during the course of hydrolysis. It is interesting to note that biosurfactant TS can maintain the surface tension in supernatants, despite its digestibility by cellulolytic enzymes. Conclusions Serving as an accelerant of lignocellulose hydrolysis, TS can also be degraded by the cellulolytic enzymes and release glucose while retaining stability, which reduces the cost of both the cellulolytic enzymes and the additive. As the glucose from the TS could be utilized by yeast, further efforts will investigate the mechanism of function and the application of TS in the production of ethanol by simultaneous saccharification and fermentation (SSF).

Four fungal strains—Trichoderma viride, Aspergillus niger, Trichoderma koningii, and Trichoderma reesei—were selected for cellulase production using furfural residues and microcrystalline cellulose (MCC) as the substrates. The filter paper activity (FPA) of the supernatant from each fungus was measured, and the performance of the enzymes from different fungal strains was compared. Moreover, the individual activities of the three components of the cellulase system, i.e., β-glucosidase, endoglucanase, and exoglucanase were evaluated. T. koningii showed the highest activity (27.81 FPU/ml) on furfural residues, while T. viride showed an activity of 21.61 FPU/ml on MCC. The FPA of the crude enzyme supernatant from T. koningii was 30% higher on furfural residues than on MCC. T. koningii and T. viride exhibited high stability and productivity and were chosen for cellulases production. The crystallinity index (CrI) of the furfural residues varied after digested by the fungi. The results indicated differences in the functioning of the cellulase system from each fungus. In the case of T. koningii, T. reesei and T. viride, furfural residues supported a better environment for cellulase production than MCC. Moreover, the CrI of the furfural residues decreased, indicating that this material was largely digested by the fungi. Thus, our results suggest that it may be possible to use the cellulases produced from these fungi for the simultaneous saccharification and fermentation of lignocellulosic materials in ethanol production.

Background As the most abundant renewable resources, lignocellulosic materials are ideal candidates as alternative feedstock for bioethanol production. Cassava residues (CR) are byproducts of the cassava starch industry which can be mixed with lignocellulosic materials for ethanol production. The presence of lignin in lignocellulosic substrates can inhibit saccharification by reducing the cellulase activity. Simultaneous saccharification and fermentation (SSF) of furfural residues (FR) pretreated with green liquor and hydrogen peroxide (GL-H2O2) with CR saccharification liquid was investigated. The final ethanol concentration, yield, initial rate, number of live yeast cells, and the dead yeast ratio were compared to evaluate the effectiveness of combining delignificated lignocellulosic substrates and starchy substrates for ethanol production. Results Our results indicate that 42.0 % of FR lignin removal was achieved on FR using of 0.06 g H2O2/g-substrate and 9 mL GL/g-substrate at 80 °C. The highest overall ethanol yield was 93.6 % of the theoretical. When the ratio of 0.06 g/g-H2O2-GL-pretreated FR to CR was 5:1, the ethanol concentration was the same with that ratio of untreated FR to CR of 1:1. Using 0.06 g/g-H2O2-GL-pretreated FR with CR at a ratio of 2:1 resulted in 51.9 g/L ethanol concentration. Moreover, FR pretreated with GL-H2O2 decreased the concentration of byproducts in SSF compared with that obtained in the previous study. Conclusions The lignin in FR would inhibit enzyme activity and GL-H2O2 is an advantageous pretreatment method to treat FR and high intensity of FR pretreatment increased the final ethanol concentration. The efficiency of ethanol fermentation of was improved when delignification increased. GL-H2O2 is an advantageous pretreatment method to treat FR. As the pretreatment dosage of GL-H2O2 on FR increased, the proportion of lignocellulosic substrates was enhanced in the SSF of the substrate mixture of CR and FR as compared with untreated FR. Moreover, the final ethanol concentration was increased with a high ethanol yield and lower byproduct concentrations.

Background As the supply of starch grain and sugar cane, currently the main feedstocks for bioethanol production, become limited, lignocelluloses will be sought as alternative materials for bioethanol production. Production of cellulosic ethanol is still cost-inefficient because of the low final ethanol concentration and the addition of nutrients. We report the use of simultaneous saccharification and cofermentation (SSCF) of lignocellulosic residues from commercial furfural production (furfural residue, FR) and corn kernels to compare different nutritional media. The final ethanol concentration, yield, number of live yeast cells, and yeast-cell death ratio were investigated to evaluate the effectiveness of integrating cellulosic and starch ethanol. Results Both the ethanol yield and number of live yeast cells increased with increasing corn-kernel concentration, whereas the yeast-cell death ratio decreased in SSCF of FR and corn kernels. An ethanol concentration of 73.1 g/L at 120 h, which corresponded to a 101.1% ethanol yield based on FR cellulose and corn starch, was obtained in SSCF of 7.5% FR and 14.5% corn kernels with mineral-salt medium. SSCF could simultaneously convert cellulose into ethanol from both corn kernels and FR, and SSCF ethanol yield was similar between the organic and mineral-salt media. Conclusions Starch ethanol promotes cellulosic ethanol by providing important nutrients for fermentative organisms, and in turn cellulosic ethanol promotes starch ethanol by providing cellulosic enzymes that convert the cellulosic polysaccharides in starch materials into additional ethanol. It is feasible to produce ethanol in SSCF of FR and corn kernels with mineral-salt medium. It would be cost-efficient to produce ethanol in SSCF of high concentrations of water-insoluble solids of lignocellulosic materials and corn kernels. Compared with prehydrolysis and fed-batch strategy using lignocellulosic materials, addition of starch hydrolysates to cellulosic ethanol production is a more suitable method to improve the final ethanol concentration.

Background: Enhancement of enzymatic digestibility by some supplementations could reduce enzyme loading and cost, which is still too high to realize economical production of lignocellulosic biofuels. A recent study indicates that yeast hydrolysates (YH) have improved the efficiency of cellulases on digestibility of furfural residues (FR). In the current work, the components of YH were separated by centrifugation and size exclusion chromatography and finally characterized in order to better understand this positive effect. Results: A 60.8% of nitrogen of yeast cells was remained in the slurry (YHS) after hydrothermal treatment. In the supernatant of YH (YHL), substances of high molecular weight were identified as proteins and other UV-absorbing compounds, which showed close molecular weight to components of cellulases. Those substances attributed to a synergetic positive effect on enzymatic hydrolysis of FR. The fraction of YHL ranged from 1.19 to 2.19 mL (elution volume) contained over 50% of proteins in YHL and had the best performance in stimulating the release of glucose. Experiment results proved the adsorption of proteins in YHL on lignin. Conclusions: Supplementation of cellulases with YH enhances enzymatic digestibility of FR mainly by a competitive adsorption of non-enzymatic substances on lignin. The molecular weight of these substances has a significant impact on their performance. Different strategies can be used for a good utilization of yeast cells in terms of biorefinery concept.