Biodegradation of cell wall components of maize stover colonized by white-rot fungi and resulting impact on in-vitro digestibility

Treatment of crop residues with some species of white-rot fungi can enhance digestibility. This study was conducted to investigate changes in in-vitro dry matter disappearance (IVDMD) and degradation of cell wall constituents in maize (Zea maize L) stover treated with three white-rot fungi: Cyathus stercoreus, Phlebia brevispora and Phanerochaete chrysosporium. Solid fermentation of maize stover for 28 days at 27°C improved IVDMD from 409 g kg^?1 (control) to 514 g kg^?1 for P brevispora and 523 g kg^?1 for C stercoreus. In contrast, growth of P chrysosporium reduced IVDMD from 409 to 298 g kg^?1. All fungi degraded cell wall p-coumaric acid (PCA) and ferulic acid (FA), but P chrysosporium was the least effective in degrading PCA and FA. Conversely, P chrysosporium degraded lignin 1·6 times more effectively than C stercoreus and 1·4 times more than P brevispora, indicating that lignin degradation alone cannot account for the IVDMD enhancement and that degradation of PCA and FA may be important. Hemicelluloses were preferentially and highly utilized by all the fungi. Cellulose was extensively degraded only by P chrysosporium (69% lost after 28 days of incubation), while substrate colonized by the other two fungi retained more than 84% original cellulose. Incubation of C stercoreus and P brevispora decreased the concentrations of both xylose and arabinose, but increased glucose concentration, whereas P chrysosporium removed less xylose and decreased glucose concentration. Preferential removal of arabinose over xylose by the fungi caused an increase in the xylose to arabinose ratio of the treated residues. Enhanced digestibility may have resulted from cleavage of lignin-carbohydrate bonds. Results of this study suggest that digestibility enhancement of maize stover colonized by white-rot fungi is regulated by a complex combination of various factors, including the degradation of structural carbohydrates, cell wall phenolic acids and lignin.     

Fungal pretreatment of wheat straw: Effects on the biodegradability of cell walls,structural polysaccharides,lignin and phenolic acids by rumen microorganisms

Disappearance of cell wall components of untreated straw and straw treated with the ligninolytic white-rot fungi Phanerochaete chrysosporium, Dichomitus squalens and Cyathus stercoreus were determined during the course of rumen digestion of samples in nylon bags. The first fungus degraded hemicelluloses and cellulose non-selectively, adversely affecting the digestion rate of crude cell walls. Dichomitus squalens and C. stercoreus preferentially degraded hemicelluloses and lignin, affording cell wall degradation rates 1.5 times higher than in native straw. Furthermore, the extent of cell wall digestion was also significantly enhanced. Both strains improved the extent of cellulose digestion, whereas the potentially degradable xylan fraction remained unchanged. Polysaccharide digestion rates were influenced in different ways depending on the strain tested: straw degraded by C. stercoreus showed an increase in cellulose digestion rate by 50%, whereas residual arabinose units were slowly degraded. Xylan was degraded 1.8 times faster in straw decayed' by D. squalens, while cellulose digestion remained unchanged. Phanerochaete chrysosporium depressed both xylan and cellulose digestion rates. Fungal-treated lignins were solubilised in the rumen faster than in untreated straw, whereas only treatment by C. stercoreus resulted in higher lignin losses. Esterified phenolic acids were extensively degraded by all three fungi. Residual ferulic and p-coumaric acids accumulated during rumen digestion, although only the former decreased in the original straw.     

Chemical composition and biodegradability of crop residues colonized by white-rot fungi

Two experiments were conducted to study the degradation of rice (Oriza sativa L) straw and maize (Zea maize L) stover by selected white-rot fungi, using loss of organic matter, disappearance of cell wall constituents, and in-vitro dry matter digestibility (IVDMD) as indices of rumen microbial degradation. Four white-rot fungi—Cyrathus stercoreus, Dichomitus squalens and two strains (cellulase-less mutant and a wild type) of Phanerochaete chrysosporium—were selected for the first experiment. After 30 days of solid state fermentation. C stercoreus increased IVDMD of both substrates from 373 g kg^?1 (rice) and 393 g kg^?1 (corn) to approximately 540 g kg^?1 by selectively degrading hemicellulose as opposed to cellulose. The highest IVDMD was obtained with a minimal loss of dry matter (33 g kg^?1). In contrast, both strains (wild and mutant) of P chrysosporium degraded cellulose and hemicellulose indiscriminately, and thus lowered the IVDMD to 276. 257 as opposed to 373 for rice straw and 301. 307 as opposed to 393 g kg^?1 for maize stover. All the fungi showed a preference for degrading maize stover compared with rice straw, although the materials were similar in cellulose and lignin concentration. No direct correlation was found between lignin degradation and the improvement of substrate IVDMD of either substrate. The objective of the second experiment was to determine the rate and extent of digestibility of rice straw colonized by C stercoreus during two incubation periods (15 and 30 days). Dry matter disappearance (DMD) was determined by ruminal incubation of the substrate contained in nylon bags. The 30-day incubation period was superior (1.3 ×) to that of the 15-day period in improving in-situ DMD. Treatment of rice straw for 30 days not only improved the extent of dry matter digestibility (616 as opposed to 389 g kg^?1), but also increased (1.5 ×) the rate of disappearance of substrate.     

Digestibility of silages in relation to their hydroxycinnamic acid content and lignin composition

BACKGROUND: The effectiveness of the analysis of cell wall‐bound hydroxycinnamic acids and the composition of lignin to evaluate the in vivo digestibility of a silage collection with unknown botanical composition was evaluated. RESULTS: Syringyl units content and total etherified phenols showed the highest correlation coefficients with in vivo dry matter digestibility (IVDMD) (r = ? 0.792 and r = ? 0.703, respectively), while guaiacyl units and total phenols showed the highest correlation coefficients with in vivo organic matter digestibility (IVOMD) (r = ? 0.871 and r = ? 0.817, respectively). Using the above‐mentioned chemical parameters, 10 equations were also developed to predict in vivo digestibility. The prediction of IVDMD produced a high adjusted R² value (0.710) using syringyl, total lignin, etherified total phenols, esterified ferulic acid and total phenol content as predictors. The prediction of IVOMD produced a higher adjusted R² value (0.821) using guaiacyl, total phenols, total ferulic acid and etherified p‐coumaric acid content as predictors. CONCLUSION: Cell wall digestibility depends on a multiplicity of factors and it is not possible to attribute a causal effect on in vivo digestibility to any single factor. However, syringyl and guaiacyl content and etherified phenols emerge as good predictors of digestibility. Copyright © 2010 Society of Chemical Industry     

嗜碱性木素降解菌降解能力的初步研究

通过比较不同嗜碱细菌对麦草中木素、纤维素和半纤维素的降解率, 并比较不同菌株的产酶及酶活情况, 筛选出了木素降解能力较强, 而纤维素和半纤维素降解能力相对较弱的嗜碱性木素降解菌。在ｐＨ≈１０－４的条件下培养８ｄ 后, 菌株６ 降解了３２－３７％ 的麦草木素, 而纤维素和半纤维素分别降解了２１－４８％ 和２２－６９％ 。这与其产酶情况基本一致, 该菌株的酶活最高, 分别为ＭｎＰ２７１－３０Ｕ／Ｌ和ＬｉＰ４１－９４Ｕ／Ｌ。     

Effect of delignification on the in vitro rumen digestion of polysaccharides of bagasse

Sugar cane bagasse was partially delignified by three different chemical methods, viz. sodium sulphide/hydroxide (Kraft process), sodium hydroxide and sodium sulphite. The Kraft and alkali treatments each reduced the lignin content by about 55%, and increased the rumen dry matter digestibility (d.m.d., measured by an in vitro method) by over 170%. Treatment of the bagasse with sodium sulphite removed only 15% of the lignin and increased the d.m.d. by only 37%. The digestibility of hemicelluloses (measured as xylan and arabinan) and cellulose in delignified bagasse increased fourfold and twofold, respectively, for the Kraft and alkali treatments and twofold for the sodium sulphite treatment.     

Fibrolytic potential of anaerobic fungi (Piromyces sp.) isolated from wild cattle and blue bulls in pure culture and effect of their addition on in vitro fermentation of wheat straw and methane emission by rumen fluid of buffaloes

BACKGROUND: Ten isolates of anaerobic fungi of Piromyces genus from wild cattle and blue bulls (five isolates from each host species) were evaluated for their fibrolytic ability in pure culture, their suitability for use as a microbial additive in buffaloes and their effect on methane emission. RESULTS: In pure culture, only two out of five isolates from wild cattle degraded wheat straw efficiently, whereas all five isolates from wild blue bulls did. Isolate CF1 (from cattle) showed the highest apparent digestibility (53.4%), true digestibility (70.8%) and neutral detergent fibre digestibility (75.0%) of wheat straw after 5 days of incubation. When added to buffalo rumen fluid, all five isolates from cattle increased (P < 0.05) in vitro apparent digestibility of wheat straw compared with the control (received autoclaved culture), but all five isolates from blue bulls failed to influence in vitro digestibility of wheat straw. Isolate CF1 showed the highest stimulating effect on straw digestion by buffalo rumen fluid microbes and increased apparent digestibility (51.9 vs 29.4%, P < 0.05), true digestibility (57.9 vs 36.5%, P < 0.05) and neutral detergent fibre digestibility (51.5 vs 26.9%, P < 0.05) of wheat straw compared with the control after 24 h of fermentation. There were also significant increases in fungal count and enzyme activities of carboxymethylcellulase and xylanase in the CF1‐added group compared with the control group. Gas and methane production g^?1 truly digested dry matter of straw were comparable among all groups including the control. CONCLUSION: Wild cattle and blue bulls harbour some anaerobic fungal strains with strong capability to hydrolyse fibre. The fungal isolate CF1 has high potential for use as a microbial feed additive in buffaloes to improve digestibility of fibrous feeds without increasing methane emission per unit of digested feed. Copyright © 2010 Society of Chemical Industry     

Biodegradation of plant cell walls,wall carbohydrates,and wall aromatics in wheat grown in ambient or enriched CO2 concentrations

Mature internodes from wheat (Triticum aestivum L) grown in control (ambient at c 370 μnol mol^?1) or enriched (to 550 μmol mol^?1) concentrations of atmospheric CO₂ in the free-air CO₂ enrichment (FACE) system were analyzed for potential changes in biodegradation of constituents due to predicted increases in atmospheric levels of CO₂. The first internodes below the grain were incubated with the lignocellulose-degrading white rot fungus, Phanerochaete chrysosporium K-3, or incubated without microorganisms. Plant samples were then analyzed for dry weight loss, disposition of specific cell types to biodegradation using electron microscopy, carbohydrates and lignin using solid state NMR spectroscopy, and ester-and ether-linked aromatics using gas chromatography. Phanerochaete chrysosporium extensively degraded stems cells (c 75%) and both carbohydrate and aromatic portions of the wheat stems; proportionately more carbohydrates were removed by the fungus from the stems. Enriched CO₂ did not affect the chemical composition of wheat stems or the biodegradation by P chrysosporium of plant cell walls or wall components for the most part. Data from various methods all indicated that enriched CO₂ did not substantially alter the biodegradation of wheat cell wall internodes or wall components. Evidence was not found for an influence on C cycling due to CO₂ concentrations in this study.     

Biodegradability of Free Monomeric and Cell-Wall-Bound Phenolic Acids in Maize Stover by Two Strains of White-Rot Fungi

Development of fungal bioconversion technology to upgrade feeding value of fibrous crop residues into animal feed requires the understanding of the impact of fungal treatments on cell wall phenolic acids. This study investigated the capacity of two strains of white-rot fungi, Phanerochaete chrysosporium and Phlebia brevispora , in degrading cell wall-bound phenolic acids in maize ( Zea maize L) stover and the free phenolic monomers in a liquid culture medium. In the study, 150 mg litre⁻¹ of p -coumaric acid (PCA), ferulic acid (FA), syringic acid (SYA), p -hydroxybenzoic acid (PHBA), vanillic acid (VA), and 200 mg litre⁻¹ of caffeic acid (CA) were added to a liquid nutrient medium and incubated with each of the fungi for 28 days. The results indicated that within 21 days the fungal treatments completely removed the added PCA and FA from the medium, and over 94% of SYA was degraded after 28 days. During the incubation periods, VA and PHBA were also extensively removed by P chrysosporium , but resistant to degradation by P brevispora . Disappearance of caffeic acid from the medium was related to both fungal degradation and abiotic hydrolysis. In the culture media, P chrysosporium was superior to P brevispora in removing the phenolic acids. Solid incubation of maize stover with the selected fungi for 28 days resulted in extensive degradation of cell-wall-bound FA and PCA. However, complete degradation of cell wall FA and PCA did not occur in maize stover. In contrast to results in pure liquid medium, P chrysosporium degraded only 20% of the initial concentration of cell wall PCA, and was less effective in degrading cell wall FA compared to P brevispora . These results indicate that the white-rot fungi were able to degrade phenolic acids both in pure culture medium and in cell wall matrix of maize stover. Furthermore, P brevispora exhibited stronger ability to degrade cell-wall-bound phenolic acids. Thus, this fungus can be more effective for the enhancement of fibre digestibility.     

Lignin Impact on Fibre Degradation: 1—Quinone Methide Intermediates Formedfrom Lignin DuringIn VitroFermentation ofCorn Stover*

Experiments were conducted to determine whether formation of quinone methide intermediates from lignin occurs during ruminal fermentation of corn stover, as indicated by nucleophilic addition reaction with sulphur-containing reducing agents. Corn stover leaf and stem fractions harvested at full maturity were incubated in buffered ruminal fluid without reducing agents or with (NH₄)₂SO₄ (S-control), Na₂S.9H₂O, cysteine-HCl (cysHCl), or cysHCl plus Na₂S.9H₂O; and in only buffer with or without cysHCl plus Na₂S.9H₂O. Mixed reducing agents (cysHCl plus Na₂S.9H₂O) enhanced ( P< 0.001) in vitro fibre degradation after 48 h, tended to increase solubilisation of fibre ( P =0.07) and dry matter ( P =0.06) in buffer alone, and elevated ( P< 0.001) S-content of residual fibre. In vitro incorporation of S into the undegraded fibre was determined for corn stover fractions of varying lignin compositions that were harvested at two maturities (early dent and full maturity) in 2 years. Extent of fibre degradation was correlated with extent of S-incorporation ( r =-0.54, P< 0.001), and with lignin methoxyl content ( r =-0.84, P< 0.001). The negative association of lignin methoxyl content with digestibility is explained by the relative likelihood of quinone methide intermediate formation from guaiacyl and syringyl units in lignin.     

Fiber and lignin analysis in concentrate, forage, and feces: detergent versus enzymatic-chemical method

Hemicelluloses, cellulose, and lignin contents of contrasting feeds, with emphasis on concentrate ingredients and complete concentrates, were analyzed using the Van Soest detergent procedure (analyzing neutral detergent fiber, acid detergent fiber, and acid detergent lignin) and the enzymatic-chemical procedure (analyzing cellulose, soluble and insoluble noncellulosic polysaccharides, and Klason lignin). Also, feces from cows fed concentrates differing in carbohydrate composition were analyzed by the 2 procedures. The correlation between acid detergent lignin and Klason lignin was significant, but not as close as the one between individual structural polysaccharides measured with the 2 procedures. The correlation between the results of the 2 procedures was highly significant for apparent cellulose digestibility, as were the correlations between digestibilities of hemicelluloses with total as well as with insoluble noncellulosic polysaccharides. The relationship between dietary lignin content and fiber digestibility was weak. The exclusion of a group of cows fed a concentrate with apple pulp, however, improved the respective correlations. Klason lignin correlated more closely with the measured fiber digestibility than acid detergent lignin. The study showed that results of the detergent method were comparable to those of the enzymatic-chemical method with cellulose, hemicelluloses, and their digestibilities. However, acid detergent lignin was much lower than Klason lignin. When the carbohydrate composition of concentrate varied widely, lignin was not suitable for the prediction of fiber digestibility.     

Evaluation of pretreatment with Pleurotus ostreatus for enzymatic hydrolysis of rice straw

The effects of biological pretreatment of rice straw using four white-rot fungi (Phanerochaete chrysosporium, Trametes versicolor, Ceriporiopsis subvermispora, and Pleurotus ostreatus) were evaluated on the basis of quantitative and structural changes in the components of the pretreated rice straw as well as susceptibility to enzymatic hydrolysis. Of these white-rot fungi, P. ostreatus selectively degraded the lignin fraction of rice straw rather than the holocellulose component. When rice straw (water content of 60%) was pretreated with P. ostreatus for 60 d, the total weight loss and the degree of Klason lignin degraded were 25% and 41%, respectively. After the pretreatment, the residual amounts of cellulose and hemicellulose were 83% and 52% of those in untreated rice straw, respectively. By enzymatic hydrolysis with a commercial cellulase preparation for 48 h, 52% holocellulose and 44% cellulose in the pretreated rice straw were solubilized. The net sugar yields based on the amounts of holocellulose and cellulose of untreated rice straw were 33% for total soluble sugar from holocellulose and 32% for glucose from cellulose. The SEM observations showed that the increase in susceptibility of rice straw to enzymatic hydrolysis by pretreatment with P. ostreatus is caused by partial degradation of the lignin seal. When the content of Klason lignin was less than 15% of the total weight of the pretreated straw, enhanced degrees of enzymatic solubilization of holocellulose and cellulose fractions were observed as the content of Klason lignin decreased.     

Fractionation and characterization of ball‐milled and enzyme lignins from abaca fibre

An Erratum has been published for this article in Journal of the Science of Food and Agriculture 79(15) 1999, 2122. Ball‐milled and enzyme lignins were produced from abaca fibre via ball milling for 6 days followed by cellulase treatment for 3 days. The crude lignin preparations were fractionated into milled lignin (ML), enzyme lignin (EL), hemicellulose‐rich milled lignin (HRML), and lignin‐rich enzyme lignin (LREL) fractions using a two‐step precipitation method instead of a traditional ether precipitation procedure. The yield and chemical composition of the resulting lignin samples are reported. The ML and EL fractions contained low amounts of associated neutral sugars (2.0–3.3%) and uronic acids (1.4–1.5%), and showed relatively low average molecular weights (2500–2660), while the LREL and HRML fractions contained large amounts of bound polysaccharides (35.6–38.3%), and showed high molecular weights (8800–25000). The four lignin fractions are composed of a large proportion of syringyl units with fewer guaiacyl and p‐hydroxyphenyl units. The ML is mainly composed of β–O–4 ether bonds between the lignin structural units. The less common β–β, β–5 and 5–5′ carbon–carbon linkages are also present in the lignin molecules. It was found that uronic acids and 41–63% of p‐coumaric acids are esterified to lignin in the three lignin‐rich fractions of ML, EL and LREL. This level increased to over 90% in the hemicellulose‐rich fraction of HRML. For ferulic acids, 92–97% were found to be etherified to lignin in the three lignin‐rich fractions of ML, EL and LREL, while in the hemicellulose‐rich fraction of HRML this reduced to only 13%, suggesting that a majority of the ferulic acids are esterified to hemicelluloses or lignin in this fraction. © 1999 Society of Chemical Industry     

经胆碱氨基酸水溶液预处理的水稻秸秆中残余木质素对多糖酶水解抑制作用的研究

本文通过考察牛血清蛋白(BSA)的添加量和不同纤维素酶用量下其添加与否对水稻秸秆残渣中多糖酶水解效率的影响,以及比较不同木质素含量的底物对纤维素酶催化行为的影响来探讨[胆碱][氨基酸]处理水稻秸秆残渣后其残留木质素对纤维素酶活性的抑制作用大小。结果发现,低酶量下,BSA的添加对纤维素和半纤维素的酶水解降解度有轻微的促进作用,分别最多提高5%及7%;而高纤维素酶用量时,其促进作用甚微。且经该类离子液体处理后的不同木质素含量的水稻秸秆基本上对酶蛋白皆无显著吸附和抑制作用。可见,该类离子液体可去除部分木质素以提高酶分子对多糖底物的可及性,此为多糖酶水解效率提高的关键因素,而该法所形成的残余木质素对酶蛋白的非特异吸附或抑制作用相对较弱。     

Cell wall composition and degradability of forage stems following chemical and biological delignification

Chemical and biological delignification methods were used to investigate the relationship between the concentration and composition of lignin and degradation of forage cell walls. Stem material from lucerne (Medicago sativa L), smooth bromegrass (Bromus inermis Leyss) and maize (Zea mays L) stalks was treated with alkaline hydrogen peroxide, potassium permanganate, sodium chlorite, sodium hydroxide, nitrobenzene, and the lignolytic fungus Phanerochaete chrysosporium. Klason lignin and esterified and etherified phenolic acids were delermined. Cell wall neutral sugar and uronic acid composition and the extent of in-vitro degradability were measured. Chemical delignification generally removed lignin. but the fungal treatment resulted in the removal of more polysaccharide than lignin. The concentrations of esterfied and etherified p-coumaric and ferulic acids were generally reduced in treated cell walls; chlorite treatment preferentially removing p-coumaric acid whereas nitrobenzene treatment removed more ferulic acid. Syringyl moieties were completely removed from the core lignin polymer by nitrobenzene treatment of forage stems. Alkaline hydrogen peroxide and nitrobenzene were generally the most effective delignification treatments for improving polysaccharide degradability, with the grass species responding similarly to delignification whereas lucerne was somewhat less responsive. Fungal delignification, under these experimental conditions, did not improve cell wall degradability of these forages. Multiple regression and covariate analyses indicated that the lignin components measured were not powerful predictors of cell wall degradability. Neither the concentration nor the composition of the lignin fractions was consistently correlated with degradation. This lack of effect was attributed to the more generalised disruption of the cell wall matrix structure by delignification treatments.     

Relationship of cell wall composition to in vitro cell wall digestibility of maize inbred line stems

The phenolic equipment of maize stem tissues was investigated in relation to the feeding value of the detergent fibre components. Sixteen maize inbred lines, including three brown‐midrib 3 mutants and their normal counterparts, were selected for highly divergent in vitro cell wall digestibility. These lines were grown during two years. Maize stems were analysed for detergent fibre concentration, esterified and etherified p‐hydroxycinnamic acids, lignin content and structure and in vitro digestibility. A large genotypic variation was found for neutral detergent fibre, cell wall phenolic composition and cell wall digestibility. Within the normal maize lines the in vitro neutral detergent fibre digestibility (IVNDFD) of stem fractions was negatively correlated with their Klason lignin content. A multiple regression model based on esterified p‐coumaric acid and lignin composition as two explanatory variates accounted for 58% of the IVNDFD variation. In this study, three normal maize inbred lines displaying a lignin content and a cell wall digestibility level close to those observed in the three bm3 lines could be detected, which opens up new breeding avenues. © 2000 Society of Chemical Industry     

Solid-state 13C NMR study of palm trunk cell walls

Trunk material from the oil palm Elaeis guineensis was dissected into parenchyma and vascular bundle fractions, which were individually examined by ¹³C solid-state nuclear magnetic resonance at low field (25 MHz). Cross-polarisation and magic-angle spinning were used with dipolar dephasing to reveal the aromatic carbons of lignin free from interference by carbohydrate. The lignin contents of the parenchyma and vascular bundles were found to be 240 g kg^?1 and 130 g kg^?1, respectively. The lignin appeared to contain a high proportion of aryl ether-linked syringyl units, but little or no ferulic or p-coumaric acid. The cellulose of both fractions had a high proportion of the crystalline component. The acetyl content was c 6 mol %C. The in-vitro digestibility of the two fractions was measured using the rumen liquor-pepsin method and was found to be low compared with forage materials: 19.5% in the parenchyma and only 11.1% in the vascular bundles.     

木聚糖酶预处理对麦草木素结构特征的影响

为了探讨木聚糖酶在麦草碱法化学机械制浆过程中的作用机理,采用13C、1H和2-DNMR光谱技术对木聚糖酶预处理麦草的二氧六环木素进行了研究。分析结果表明:麦草经木聚糖酶处理,木素的羟基和甲氧基数量增加。木聚糖酶处理是"生物"作用,在酶攻击麦草的木素-碳水化合物复合体的脂键或糖键、部分脱出木糖的同时,麦草被"活化"。高清晰度的2D-HMQC NMR技术是分析木素结构的有利工具。     

有机溶剂法麦草木质素的化学特性研究

用不同浓度的乙酸-水、甲酸-乙酸-水、甲醇-水及乙醇-水溶液处理脱蜡的麦草,获得的木质素采用FT-IR、~1H-NMR、~(13)C-NMR及化学法研究其化学特性,结果表明,有机酸溶液比有机醇溶液脱木素作用更加广泛,能选择性降解麦草中的纤维素、木质素及半纤维素。甲酸对木质素的溶解有显著影响。随着乙酸或甲酸浓度的增加,愈创木基结构单元增加,木质素缩合。有机醇处理获得的木质素中,含有几乎等量的非缩合型愈创木基和紫丁香基结构单元及少量的对羟苯基结构单元。     

Effect of chemical pretreatments on the fermentation and ultimate digestibility of bagasse by Phanerochaete chrysosporium

When sugarcane bagasse was pretreated at room temperature with various chemicals singly or in combination, (0.25 m NaOH; 0.5 m H₂SO₄; 2.6 M NH₃;0.14 M Ca(OH)₂+0.12 M Na₂CO₃;4.2 m EDA; and 0.5 M H₂SO₄ or 0.25 M NaOH followed by 4.2 M EDA), increases in in-vitro digestibility range from 28.9 to 48.6% depending on the particular chemicals. With most pretreatments, the hemicellulose content decreased and the cellulose content increased slightly, while lignin levels decreased only with NaOH + EDA pretreatments. Further fermentation of the chemically pretreated bagasse with Phanerochaete chrysosporium gave increased digestibilities, the highest final digestibility (59%) being achieved by pre-treatment with 0.25 M NaOH. Pretreatment with NaOH or Ca(OH)₂+Na₂CO₃ and fermentation gave greatly increased levels of hemi-cellulose and cellulose and substantial decreases in lignin levels. Chemical pretreatments of bagasse together with autoclaving considerably enhanced in-vitro digestibility (up to 75%) and lignin degradation (1.4%). Pretreatment with NaOH, Ca(OH)₂+Na₂CO₃, and EDA plus autoclaving gave large increases in total hemicelluloses and cellulose and marked decreases in lignin. Further fermentation with P. chrysosporium gave only slight increases in digestibility.