白腐菌胞外酶降解木素的机制及其协同作用

白腐菌是唯一能完全降解木质纤维素的微生物,其分泌的胞外酶对木素的降解倍受关注。木质纤维素中木素的降解是多种生物酶作用的结果,文中叙述了漆酶、多种过氧化物酶、产过氧化氢的氧化酶等胞外酶的作用机制,以及这些酶之间存在的广泛而复杂的协同作用。     

几种产木素降解酶白腐菌对碱木素的降解研究

白腐菌分泌胞外氧化酶——木素降解酶。这类氧化酶底物专一性不强，除降解木素外还降解大量的污染物。首先观察4种白腐菌Pleurotus eryngii,Polyporus versicolor，Pleurotus ostreatus和Fomes lignosus在限氮和富氮培养基中产木素过氧化物酶、锰过氧化物酶和漆酶的能力，4种真菌只产锰过氧化物酶和漆酶。由于Pleurotus eryngii喇和Pleurotus eryngii产酶能力较强，用于碱木素的降解脱色，二者在限氮条件下11天对碱木素降解脱色率为65％和72％。0．6g／L Ca^2 有助于菌体生物量的增加，对产酶影响不明显；10mg／L Mn^2 有助于锰过氧化物酶活性的提高：5mg／L Cu^2 可显著提高菌体产漆酶能力，10天可使碱木素的降解脱色率达到90％。     

木素降解酶在制浆漂白中的应用

木素降解酶的生物漂白是通过木素降解酶的直接氧化和降解纸浆中的残余木素,以降低纸浆的卡伯值,提高纸浆白度或有利于后续化学漂白剂的漂白,提高可漂性.本文着重介绍了三种木素降解酶在漂白中的应用.     

木素模型物及其在制浆中的应用研究进展

木素是自然界储量仅次于纤维素和甲壳素的天然大分子聚合物。从化学结构上看,木素由愈创木基、对羟苯基和紫丁香基三种结构单元以醚键和碳碳双键连接而成,结构十分复杂,且在植物原料中,木素与纤维素和半纤维素紧密地联系在一起,利用现有手段很难分离出纯木素。木素对制浆过程,尤其是对蒸煮和纸浆漂白有重要影响,为深入理解木素在制浆过程中发生的化学反应机理及其结构变化,需要借助木素模型物进行木素的相关研究。本文综述了国内外木素模型物的研究现状,论述了木素模型物在制浆过程中木素-碳水化合物复合体(LCC)的生成及漂白过程中反应机理等相关研究中的应用情况。     

乙酸法制浆副产物半纤维素降解糖的初步研究

乙酸法制浆是分离木质纤维素原料的主要组分-木素、纤维素、半纤维素,以便于其进一步利用的简单、可行的方法。本文主要研究了乙酸法分离得到的半纤维素降解糖的特点,利用较新型的离子色谱法分析了半纤维素降解糖中的单糖组成和含量;利用超滤系统进行了半纤维素降解糖的初步分级及相对质量百分含量测定,分析了其分子量分布情况;利用红外光谱对半纤维素降解糖结构进行了一定的分析。     

木聚糖酶、木素酶预处理制备硫酸盐浆的研究

木聚糖酶、木素降解酶和纤维素酶等处理蔗渣原料进行酶法化学制浆,可节省氢氧化钠和硫化钠各21．4％。木聚糖酶剂量20-501U／g较为合适,木素降解物结构鉴定显示,不同木素降解酶对木素作用位点和矿化作用力不同,是其处理效果差异的本质原因。     

降解芦苇木素复合菌种的选育

选用普通青霉菌(A)、产黄青霉菌(B)、向病菌(C)和烟曲霉菌(D)作为实验菌种对芦苇木素进行降解。通过对4种菌种进行不同比例的复合制成复合菌,比较木素降解率,从而确定最佳复合菌。然后进行复合菌种不同复合方式、不同复合比例和固液比的优化,得到最佳复合菌。结果表明,ABD复合菌木素降解率最高,ABD复合菌在8天、复合比例为A∶B∶D=1∶4∶16时,木素含量为10.7%,降解率达67.3%。     

分批与流加发酵法生产纤维素酶的研究

采用里氏木霉ＲｕｔＣ－３０,对２．５Ｌ罐分批和流加发酵产酶条件及优化进行了系统研究。通过研究不同浓度的ＳｏｌｋａＦｌｏｃ（纤维素粉）对分批发酵产酶的影响,发现菌体浓度与产酶量随底物浓度增加而增加,当采用５０ｇ／ＬＳｏｌｋａＦｌｏｃ复合１０ｇ／Ｌ麸皮为碳源时,菌体浓度和产酶量最大,最大ＤＣＷ１３．８２ｇ／Ｌ,ＣＭＣａｓｅ２３４．２Ｕ／ｍｌ,ＦＰＡ２１．２５Ｕ／ｍｌ,但ＳｏｌｋａＦｌｏｃ增加至６０ｇ／Ｌ,高浓度底物对菌体初始生长产生强烈抑制,产酶下降。通过研究不同初始Ｓｏｌ－ｋａＦｌｏｃ浓度对流加发酵产酶的影响,发现当初始底物浓度为５０ｇ／ＬＳｏｌｋａＦｌｏｃ复合１０ｇ／Ｌ麸皮时,菌体量和产酶均达到最大值,分别为ＤＣＷ１５．４１ｇ／Ｌ,ＣＭＣａｓｅ３５９．７Ｕ／ｍｌ,ＦＰＡ３０．６Ｕ／ｍｌ,高菌体量是获得纤维素酶高产的关键因素之一。此外用硫铵盐析法对纤维素酶进行了提取。     

采用TiO2／ZnO光催化降解蒸煮废液中木素

印度Panjab大学化学工程和技术系科技人员采用TiO2或ZnO半导体光催化降解麦草硫酸盐蒸煮废液中的木素,发现ZnO比TiO2光催化降解蒸煮废液中木素的效果更好。试验了各种不同参变数包括催化剂用量、废液pH值、氧化剂浓度和木素起始浓度。在pH值为11时有利于木素降解。催化剂最佳用量为1g／L。     

生物质原料的酶解及其在制浆造纸工业中的应用

纤维素、半纤维素和木素是主要的生物质原料,它们对自然界的碳循环是必不可少的.每种聚合物都可被能产生协同作用的酶系的多种微生物降解.不久的将来,基于微生物和酶的新工艺会引起新的环境友好技术.主要介绍了三大生物质原料的生物降解所需要的微生物和酶,对主要酶的作用机制和分子生物学进展也进行了阐述,另外概述了基于木质纤维原料酶水解的生物制浆和生物漂白的研究进展.     

木质素与半纤维素对稻草秸秆酶解的影响

分别采用稀酸和酸碱顺序两种方法处理稻草秸秆,20 FPU/g(底物干重)的纤维素酶、底物质量浓度为80 g/L,45℃酶解72 h。结果表明,木质素与半纤维素对纤维素转化为葡萄糖都有较大影响,稀酸处理的秸秆酶解纤维素转化率(43.4%,葡萄糖质量浓度24.1 g/L)是未处理秸秆(16.8%,葡萄糖质量浓度6.2 g/L)的2.6倍,而酸碱顺序处理的秸秆(60.6%,葡萄糖质量浓度47.7 g/L)则是未处理秸秆的3.6倍。采用上述两种方法处理秸秆后,秸秆木质素和半纤维素被移去,秸秆结构发生改变,从而秸秆纤维更易受纤维素酶的攻击,并且秸秆木质素和半纤维素质量分数越低,纤维素的酶解得率就越高。     

Effect of seed culture on solid-state bioconversion of wheat straw by Phanerochaete chrysosporium for animal feed production

The solid-state bioconversion of wheat straw by Phanerochaete chrysosporium for the production of animal feed was studied. This study was performed based on a central composite experimental design. The conditions of the seed culture most suitable for rapid induction of the ligninolytic activity of the fungus, when the seed culture is subsequently used for solid-state bioconversion of wheat straw, were determined. When the seed culture with an initial pH of 5.8 was grown under agitated conditions at 130 rpm in baffled flasks at 38 degrees C, it was predicted to give lignin degradation of 19.5% and cellulose degradation of 17.8%. A time profile study of the solid-state bioconversion of wheat straw indicated that the highest lignin and lowest cellulose degradation levels occurred on the sixth day of cultivation. The desirability coefficient for this process also passed through a maximum of 0.705 on the sixth day.     

白腐菌对稻草秸秆中木质纤维素降解规律的研究

通过对傅里叶变换红外光谱(FTIR)谱图的分析和木质纤维素组分含量变化的测定,研究了3株白腐菌在50天培养期内降解稻草中木质纤维素的规律。结果表明,3株白腐菌对稻草秸秆中木质纤维素的降解具有一定的顺序和选择性,先降解半纤维素和木质素,再同时降解半纤维素、纤维素和木质素。从降解比例来看,白腐菌对半纤维素和木质素具有很好的降解优势,对半纤维素有较好的降解选择性。     

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.     

Structural changes in wheat straw components during decay by lignin-degrading white-rot fungi in relation to improvement of digestibility for ruminants

Structural changes and resulting in-vitro dry matter digestibility (IVDMD) were determined during the course of solid-state fermentation of wheat straw using the lignin-degrading white-rot fungi Sporotrichum pulverulentum, Pycnoporus cinnabarinus and Cyathus stercoreus. The first fungus grew very rapidly on straw but degraded hemicelluloses and cellulose non-selectively resulting in very low IVDMD increases (50% after 35% weight loss). P. cinnabarinus and C. stercoreus preferentially degraded hemicelluloses achieving high improvements in IVDMD (maximum increase of 63 and 94%, respectively) with limited dry weight losses (12 and 18% after 7 and 13 days, respectively). The three fungi exhibited some selectivity among the individual hemicellulose components: O-acetyls were removed essentially at the same rate as xylan, while uronic acids accumulated as incubation proceeded. Conversely, the arabinose content decreased rapidly, especially with C. stercoreus and P. cinnabarinus, suggesting that removal of this pentose was partly responsible for digestibility improvement. Esterified phenolic acids were rapidly degraded during the first stages of decay by all three fungi although P. cinnabarinus and C. stercoreus degraded ferulic acid faster than p-coumaric acid. Lignin was preferentially degraded compared to polysaccharides by all three fungi. The amount of lignin removed, as determined by Klason, correlated well with IVDMD improvement (r=?0.97), while acid detergent lignin (ADL) showed a lower correlation (r=-0.86). Acidolysis yields of decayed lignin pointed to preferential degradation of β-O-4 ether linked units by the fungi. Syringyl units were removed faster than guaiacyl units only after 5 to 10% weight loss was obtained.     

Inter-relationships between acidic and alkali treatments of cotton straw and wheat straw and their fibre chemical properties

The amount of lignin in the cell walls of cotton straw (CS) and wheat straw (WS) was found to be the same, but the ratio between lignin and hemicellulose was considerably lower in CS than in WS. In CS the amount of soluble acid lignin was less than 1% of the total lignin, whereas in WS it was 20%. The amount of phenolics in concentrated sulphuric acid (72%) hydrolysates of the cell wall was reduced drastically in WS compared with the amount released by diluted (1 N) sulphuric acid; this may have been due to polymerisation of low-molecular-size lignin. The amount of alkali-soluble lignin in WS was 3–7 times greater than in CS. Following acid treatment the amount of alkali-soluble lignin was reduced from 20% of the total content to 5% in WS, and from 5% to 1% in CS. Enzymic hydrolysis was 49% higher in WS cell wall than in CS cell wall. In WS, acidic and alkali pretreatments followed by cellulase treatment increased glucose yield from cellulose by 260% and 280%, respectively. In CS, acidic pretreatment did not affect the glucose yield from cellulose, whereas alkali treatment increased it by 35%.     

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.     

不同Cu离子浓度和pH值对云芝降解秸秆中木质素和纤维素的影响

云芝(Coriolus versicolor)对秸秆中木质素与纤维素的降解情况受不同Cu2+浓度和pH值条件的影响,设定不同条件可以提高木质素的降解率,降低纤维素的降解率,以更好地保存纤维素的完整性,实现秸秆中主要成分的分离。通过均匀设计法,设定不同的Cu2+浓度环境X1(0、1.0、2.0、4.0、6.0mmol/L)和不同pH值条件X2(2.2、2.8、3.4、4.0、4.6),测定相应条件下云芝的菌丝生长情况、木质素酶活力、纤维素酶活力以及秸秆中木质素和纤维素的降解率。结果表明：木质素的降解率与Cu2+浓度呈正相关,与pH值呈负相关;纤维素的降解率与pH值呈正相关,与Cu2+ 浓度呈负相关。通过试验所得方程预测得知,Cu2+浓度6mmol/L、pH2.2是优化的云芝降解、分离秸秆中主要成分的条件,在该条件下,由所得方程可知秸秆中木质素的降解率为16.1%,纤维素的降解率为27.7%。     

制取可降解纤维地膜的秸秆纤维特性研究

原料的特性在很大程度上决定了产品的特性及加工工艺,因此对制成可降解纤维地膜的原料秸秆纤维进行物理化学及机械打浆特性研究具有重要意义。本研究采用Leica显微镜测定秸秆纤维形态,SPSS17．0统计分析纤维长宽比,Design-expert6．0．10区组对比分析两种秸秆、纤维间理化及机械打浆特性差异和经机械加工后纤维成...     

Chemical composition of some forages and various residues from feeding value determinations

NDF, ADF, ‘cellulose’ and IVOMD residues, from feeding value determinations, were prepared from some forages, including straw, alkali-treated straw, grass and lucerne samples. The crude protein, cellulose, hemicellulose, uronic acid, Klason lignin, lignin and ash contents of these residues and the corresponding original forage samples were determined together with the relative composition of the neutral sugar constituents after acid hydrolysis. Cellulose, hemicellulose and Klason lignin were the main components in the NDF fractions but substantial amounts of crude protein (1–6%) also remained. Cellulose and Klason lignin were the main components in the ADF fractions, but 7–14% of the fractions was hemicellulose and 1–4% crude protein. Cellulose was the main component in the ‘cellulose’ fractions, but they also contained 8–13% hemicellulose, 2–7% Klason lignin and 2–11% ash. The composition of the IVOMD residues showed that cellulose and hemicellulose had been dissolved to about the same amounts (70–80%) and that most of the Klason lignin remained.