Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian countries, it is burnt on fields causing harm to the environment. Rice straw contains lignin, ...cellulose, hemicelluloses, and silicates making it recalcitrant. Pretreatment processes disintegrate lignin-carbohydrate matrix for efficient bioconversion of polysaccharides to fermentable sugars. A good number of physical, biological and chemical processes have been tried but degradation of polysaccharides and subsequent fermentation is still a challenge. Alkaline pretreatment causes effective delignification and swelling of biomass. The present study was performed on alkaline pretreatment of rice straw with 1% NaOH by autoclaving for 30 min at 121 °C at 10% solid loading. It was extracted with water to remove lignins, solids separated by filtrations and washed again to neutralize the pH. Water washing also led to removal of phenolic inhibitors. High (63%) glucan enrichment was obtained with concomitant lignin loss. Dry matter loss was around 50%. Enzymatic saccharification of the pretreated solids at 5 and 10% with Accellerase® 1500 for 24 h at 50 °C gave saccharification efficiency 76 and ~ 50% respectively. Hydrolysates containing 18 and 23 gL
−1
sugars, supplemented with minimal salts, yeast extract, fermented by
S. cerevisiae
LN for 24 h yielded ~ 2 and 4 gL
−1
ethanol with fermentation efficiency 55–66%. Thus, NaOH pretreatment is a cost effective option for ethanol production from rice straw. Lignin removed in prehydrolysates can be recovered by acidification.
As world moves toward increasing number of products being produced from renewable lignocellulosic agricultural and forest residues, the major classes of products that will shift to greener routes on ...priority are energy, fuels, and materials in that order. In materials segment, polyhydroxyalkanoates are an emerging class of biopolyesters with several potential industrial uses. The present work investigates medium chain length polyhydroxyalkanoates (mcl-PHA) producing capabilities of Pseudomonas putida KT2440 from a mixture of compounds produced from lignocellulosic biomass deconstruction. The hydrolysates obtained from nitric acid pretreatment of lignin rich cotton stalk (CS) and palm empty fruit bunch (EFB) were used as substrates for production of mcl-PHA. Presence of 3-hydroxydecanoate and 3-hydroxyocytanoate observed on GC-MS confirmed PHA accumulation in the cells. PHA accumulation was estimated between 20% and 35% of cell dry weight when grown on both model substrates as well as biomass hydrolysates. PHA titers obtained on hydrolysates of CS and EFB were 0.24 g/L and 0.21 g/L, respectively.
Lignocellulosic biomass provides attractive nonfood carbohydrates for the production of ethanol, and dilute acid pretreatment is a biomass‐independent process for access to these carbohydrates. ...However, this pretreatment also releases volatile and nonvolatile inhibitors of fermenting microorganisms. To identify unique gene products contributing to sensitivity/tolerance to nonvolatile inhibitors, ethanologenic Escherichia coli strain LY180 was adapted for growth in vacuum‐treated sugarcane bagasse acid hydrolysate (VBHz) lacking furfural and other volatile inhibitors. A mutant, strain AQ15, obtained after approximately 500 generations of growth in VBHz, grew and fermented the sugars in a medium with 50% VBHz. Comparative genome sequence analysis of strains AQ15 and LY180 revealed 95 mutations in strain AQ15. Six of these mutations were also found in strain SL112, an independent inhibitor‐tolerant derivative of strain LY180. Among these six mutations, null mutations in mdh and bacA were identified as contributing factors to VBHz tolerance in strain AQ15, based on the genetic and physiological analysis. The deletion of either gene in strain LY180 increased tolerance to VBHz from approximately 30–50% (vol/vol). Considering the location and physiological role of the two enzymes in the cell, it is likely that the two enzymes contribute to the VBHz sensitivity of ethanologenic E. coli by different mechanisms.
Increased tolerance of engineered E. coli to biomass acid hydrolysate.
•Reduced and non-reduced forms of biomass compounds were evaluated in APR.•Reduced feeds produced significantly higher gas yield with high hydrogen selectivity.•Biomass hydrolysate exhibited better ...performance than glucose.•Ru/C catalyst was more active than Pt/Al2O3 for reduced biomass feeds.
There has been increasing interest in the production of gaseous and liquid biofuels from biomass. Biomass feed type and its content to be used in the conversion process are very important parameters to produce high yield biofuel. In this study, reduced and non-reduced forms of biomass-derived compound (glucose) and actual biomass hydrolysate feeds were evaluated to produce hydrogen-rich gas mixture by aqueous-phase reforming (APR) in presence of supported Ru catalyst. Various hydrogenation conditions were tested for effective conversion. The results showed that reduced solutions always produced significantly higher gas yield with high hydrogen selectivity. Although biomass hydrolysate was composed of variety of complex compounds, it exhibited significantly better performance compared to glucose, simple biomass model compound.
An industrial ethanol-producing
Saccharomyces cerevisiae
strain with genes of fungal oxido-reductive pathway needed for xylose fermentation integrated into its genome (YRH1415) was used to obtain ...haploids and diploid isogenic strains. The isogenic strains were more effective in metabolizing xylose than YRH1415 strain and able to co-ferment glucose and xylose in the presence of high concentrations of inhibitors resulting from the hydrolysis of lignocellulosic biomass (switchgrass). The rate of xylose consumption did not appear to be affected by the ploidy of strains or the presence of two copies of the xylose fermentation genes but by heterozygosity of alleles for xylose metabolism in YRH1415. Furthermore, inhibitor tolerance was influenced by the heterozygous genome of the industrial strain, which also showed a marked influenced on tolerance to increasing concentrations of toxic compounds, such as furfural. In this work, selection of haploid derivatives was found to be a useful strategy to develop efficient xylose-fermenting industrial yeast strains.
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A headspace gas chromatography (HS-GC) method is developed for determination of formic acid (FA) and acetic acid (AA) in biomass hydrolysate. The method is based on the “in-vial” ...derivatization reaction of alcohols and acids. NaHSO4/ethanol is selected as the preferred derivatization reagent. The method has a reproducibility of RSD <0.87% and recovery of 97.1%–103.1%. The limits of the quantification were 2.02 and 2.38mg/L for FA and AA, respectively. The GC analysis time only required 12.4min. The method is rapid, sensitive and suitable for measuring FA and AA in the multifarious biomass hydrolysates in pulping and biorefinery industries.
Tuna protein hydrolysate (TPH) was prepared by hydrolysis with Prolyve BS and fractionated by membranes process. The antioxidant activities of recovered peptide fractions were evaluated. Four novel ...antioxidant peptides that were isolated from nanofiltration retentate exhibited the highest antioxidant activity, using gel chromatography and reversed phase high-performance liquid chromatography. The amino acid sequences of isolated peptides were identified as Tyr-Glu-Asn-Gly-Gly (P2), Glu-Gly-Tyr-Pro-Trp-Asn (P4), Tyr-Ile-Val-Tyr-Pro-Gly (P7) and Trp-Gly-Asp-Ala-Gly-Gly-Tyr-Tyr (P8) with molecular weights of 538.46, 764.75, 710.78 and 887.85 Da, respectively. P2, P4, P7 and P8 exhibited good scavenging activities on hydroxyl radical (IC
50
0.41, 0.327, 0.17 and 0.042 mg/ml), DPPH radical (IC
50
0.666, 0.326, 0.451 and 0.377 mg/ml) and superoxide radical (IC
50
0.536, 0.307, 0.357 and 0.115 mg/ml). P7 was effective against lipid peroxidation in the model system. The isolated peptides might be useful used as natural food additive in food industry and formulation of nutritional products.
Alkaline pretreatment and sequential enzymatic hydrolysis of soybean hull were investigated to obtain fermentable sugars for polyhydroxyalkanoates production along with residual glycerol as low-cost ...carbon sources. Soybean hull is composed of approximately 32% cellulose, 12% hemicellulose, 6% lignin, and 11% protein. Alkaline pretreatment was carried out with 2% NaOH concentration, 10% (w/v) biomass loading, and 60 min incubation time in an autoclave at 120 °C. The response surface methodology (RSM) based on the central composite design (CCD) tool was employed to optimize the enzymatic hydrolysis process, where the variables of biomass loading, enzymes’ concentration, and time were considered. The maximum total reducing sugars concentration obtained was 115.9 g∙L−1 with an enzyme concentration of 11.5 mg protein/g dry substrate for enzyme preparation B1, 2.88 mg protein/g dry substrate for XylA, and 57.6 U/g dry substrate for β-glucosidase, after 42 h at 45 °C, and pH was 4.5. Subsequently, the saccharification step was conducted by increasing the processing scale, using a 1 L tank with stirring with a controlled temperature. Implementing the same enzyme concentrations at pH 4.5, temperature of 45 °C, 260 mL working volume, and incubation time of 42 h, under fed-batch operation with substrate feeding after 14 h and 22 h, a hydrolysate with a concentration of 185.7 g∙L−1 was obtained. Initially, to verify the influence of different carbon sources on Cupriavidus necator DSMz 545 in biomass production, batch fermentations were developed, testing laboratory-grade glucose, soybean hull hydrolysate, and waste glycerol (a by-product of biodiesel processing available in large quantities) as carbon sources in one-factor-at-a-time assays, and the mixture of soybean hull hydrolysate and waste glycerol. Then, the hydrolysate and waste glycerol were consumed by C. necator, producing 12.1 g∙L−1 of biomass and achieving 39% of polyhydroxyalkanoate (PHB) accumulation. To the best of our knowledge, this is the first time that soybean hull hydrolysate has been used as a carbon source to produce polyhydroxyalkanoates, and the results suggest that this agro-industrial by-product is a viable alternative feedstock to produce value-added components.
Inhibitors are formed that reduce the fermentation performance of fermenting yeast during the pretreatment process of lignocellulosic biomass. An exometabolomics approach was applied to ...systematically identify inhibitors in lignocellulosic biomass hydrolysates.
We studied the composition and fermentability of 24 different biomass hydrolysates. To create diversity, the 24 hydrolysates were prepared from six different biomass types, namely sugar cane bagasse, corn stover, wheat straw, barley straw, willow wood chips and oak sawdust, and with four different pretreatment methods, i.e. dilute acid, mild alkaline, alkaline/peracetic acid and concentrated acid. Their composition and that of fermentation samples generated with these hydrolysates were analyzed with two GC-MS methods. Either ethyl acetate extraction or ethyl chloroformate derivatization was used before conducting GC-MS to prevent sugars are overloaded in the chromatograms, which obscure the detection of less abundant compounds. Using multivariate PLS-2CV and nPLS-2CV data analysis models, potential inhibitors were identified through establishing relationship between fermentability and composition of the hydrolysates. These identified compounds were tested for their effects on the growth of the model yeast, Saccharomyces. cerevisiae CEN.PK 113-7D, confirming that the majority of the identified compounds were indeed inhibitors.
Inhibitory compounds in lignocellulosic biomass hydrolysates were successfully identified using a non-targeted systematic approach: metabolomics. The identified inhibitors include both known ones, such as furfural, HMF and vanillin, and novel inhibitors, namely sorbic acid and phenylacetaldehyde.
We report here the production of pure (R,R)-2,3-butanediol (2,3-BDO) isomer by the non-pathogenic Paenibacillus polymyxa ICGEB2008 using lignocellulosic hydrolysate as substrate. Experimental design ...based on Plackett-Burman resulted in identification of Mn and K as most crucial salt elements along with the yeast extract for 2,3-BDO production. Further experiments using Box-Behnken design indicated that both KCl and yeast extract together had major impact on 2,3-BDO production. Optimized medium resulted in 2,3-BDO production with 2.3-fold higher maximum volumetric productivity (2.01 g/L/h) and similar yield (0.33 g/g sugar) as compared to rich yeast extract-peptone-dextrose medium in the bioreactor studies. Considering that the balance substrate was channeled towards ethanol, carbon recovery was close to theoretical yield between the two solvents, i.e., 2,3-BDO and ethanol. Biomass hydrolysate and corn-steep liquor was used further to produce 2,3-BDO without impacting its yield. In addition, 2,3-BDO was also produced via simultaneous saccharification and fermentation, signifying robustness of the strain.
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