微波预处理稻壳对纤维素酶固态发酵的影响

以稻壳为原料,通过微波预处理后用于固态发酵生产纤维素酶,研究了微波处理对后续发酵过程的影响。采用正交试验与单因素试验确定了微波处理的条件,并分析了微波功率与处理时间对发酵过程中纤维素酶活性及戊糖、还原糖含量的影响。试验结果表明,用功率为300W的微波处理稻壳7min后进行发酵,可以得到最高的纤维素酶酶活,其中滤纸酶活（干基质）可达7．09 IU／g,CMC酶活（干基质）可达87．24 IU／g,分别比未经处理的稻壳提高了21％和15％。若以单位能耗产生的酶活增加量计算,微波处理稻壳5min后发酵,可以得到最高的酶活性增加量。     

基于响应面法对秸秆纤维素乙醇生产工艺参数的优化

文章在对里氏木霉T12菌株产纤维素酶的培养条件进行单因素优化的基础上,以滤纸酶活力(FPA)为响应值,通过Plackett-Burman设计法筛选出对产酶影响最显著的3个因素,依次为麦麸>温度>氯化钙。响应面优化结果为当麦麸、温度、氯化钙分别为6.27 g/L,31℃,0.709 g/L时,纤维素酶理论最大FPA酶活为62281.3 U/m L。在优化后的培养条件下纤维素酶粗酶液的实际FPA酶活为60 126.5±16.0 U/m L。将纤维素酶粗酶液以10%添加量加入秸秆一步转化乙醇的5 L发酵罐中,经过144 h的发酵,乙醇产量(v/v)可达到7.05%±0.18%。     

混合固态发酵降解甘蔗渣产糖产乙醇研究

以碱处理甘蔗渣为原料,比较里氏木霉(Trichoderma reesei CICC40359)和斜卧青霉(Penicillium decumbens LSM-1)单菌和混菌固态发酵及转化乙醇效果,研究发酵过程菌体生长、产酶产糖和乙醇转化情况。结果表明:混菌发酵效果优于单菌,在接种量8%,发酵温度30℃,混菌固态发酵(SSF)72h后总糖和还原糖产量最大值为20.21 g/L和12.47 g/L;β-葡萄糖苷酶活力和菌体生物量在144 h后分别达到0.48 IU/m L和0.21 g/g DM;对发酵3 d后底物(包括生成糖、合成酶及未降解基质)接种酵母进行乙醇同步糖化发酵,乙醇浓度在发酵24 h时达到5.83 g/L,发酵效率达到理论值的40.84%。利用多菌混合固态发酵转化底物产乙醇能避免传统乙醇生产过程高成本纤维素酶的应用,为纤维乙醇生产提供一条经济有效的新途径。     

固态发酵产酶反应中体系传热传质行为分析

固态发酵是纤维素类生物质转化的有效途径,具有用水量少、容积产率高等优点。固态发酵生产纤维素酶一般是液态发酵酶产量的近3倍,可大幅降低酶的生产成本。在固态发酵过程,微生物在缺水环境中生长,发酵底物和接种物之间存在异质性,导致发酵热量分布不均匀、发酵过程氧气与中间产物不易扩散等问题。基于此,重点对固态发酵反应中体系传热传质方式及其影响因素进行了分析,并探讨其强化方法。根据传热方式,总结了发酵罐适用的导热微分方程及传热模拟方法,并分析气泡和颗粒基质中的传质过程及其限速步骤以及解决传质限速的途径。反应体系传热传质机理研究可促进固态发酵技术产业化应用进程。该研究可为有机废弃物固态发酵技术研究及应用提供一定的理论和技术支持。     

优化产酶培养基用于稻草发酵产乳酸的研究

对利用稻草为碳源发酵产纤维酶的过程从菌种选择、培养基的选择、碳源的结构、含水率进行了优化。以黑曲霉及里氏木霉的混合菌株为产酶菌种,在稻草粉和麦麸以3:1的比例混合作碳源,培养基中含水率为70%时发酵产出的纤维素酶酶活达到最高,最高的Cx酶活为1568.47U/g,滤纸酶活为489.3U/g。以该条件下产的纤维素酶分别用短乳杆菌和米根霉进行乳酸发酵实验,产乳酸结果为:短乳杆菌:10.8g/L;米根霉:9.2g/L。     

沼气发酵过程中几种水解酶活性的变化规律研究

研究了猪粪的沼气发酵过程中几种水解酶活性的变化。结果表明，酶活性大小与沼气产量的大小是相关的。各种酶酶活最大时，产气量正好处于高峰。其中酸性和中性蛋白酶酶活力发酵第５天呈现象最大，分别为１０．４和６．７μｇ酷氨酸／（ｍＬ．ｍｉｎ）；碱性蛋白酶酶活在发酵第１４天呈现最大，为９．３μｇ酷氨酶／（ｍＬ．ｍｉｎ）；脂肪酶酶活最大值亦在第１４天，为９１．１８μｇ脂肪酸／（ｍＬ．ｍｉｎ）；纤维素酶麦活出现滞后     

一株高活力纤维素酶产生茵-链霉菌C-5产酶研究

以链霉菌(Streptomyces sp.)C-5为实验材料,稻草粉为唯一诱导碳源培养基,采用液体摇瓶发酵法,对其产纤维素酶进行了单因素优化试验和四因素三水平正交设计优化试验.C-5的最佳培养条件为:稻草粉5%(w/v),豆饼粉1.5%(w/v),初始pH为7.5,培养温度31℃.在此最佳培养条件下C-5的CMCase酶活达到了41.37U,是优化前CMCase酶活的3.32倍.链霉菌C-5的产酶进程长,酶活维持较高水平可达10d以上.因此,利用该菌生产纤维素酶具有一定的优越性,对提高秸秆的资源利用率有良好的应用前景.     

木质纤维素酶水解分形动力学的研究进展

酶水解作为发酵法生产燃料乙醇的关键步骤之一,其高效的转化过程对后续糖发酵至关重要,酶水解动力学研究可为高效转化机理的研究提供理论支持。但纤维素酶水解是一个复杂的多相异质反应过程,很难用简单的动力学模型进行表征。由于酶分子表面具有分形特性,其与分形动力学具有局部相似性,因此,分形理论可为木质纤维素酶水解的复杂动力学研究提供理论基础。从纤维乙醇生产工艺出发,在分析木质纤维素酶水解机理及影响酶解效率主要因素的基础上,总结了国内外分形动力学目前用于木质纤维素类生物质酶水解过程的主要动力学模型研究进展,并对其发展趋势和应用前景进行了展望。     

绿色木霉的选育及固态发酵产纤维素酶的研究

从纤维素酶产生菌绿色木霉TY-2出发,通过紫外诱变技术选育出1株遗传稳定性良好的高产菌株H-28,其产纤维素酶的滤纸酶活力稳定在2.67 U/g左右,较出发菌株提高58.08%。以麸皮和蔗渣为主要原料对变异株H-28进行固态发酵研究,单因素优化了培养基、培养条件和表面活性剂对菌株H-28发酵产纤维素酶的影响,最后选取影响产酶较大的4个因素:发酵时间、Mandels营养盐液、蛋白胨、吐温-80做4因素3水平正交试验。最终优化后突变菌株H-28的产酶能力最高值为6.79 U/g,是出发菌株的4.07倍。     

里氏木霉和黑曲霉降解香蕉秆产可发酵糖的研究

研究了里氏木霉和黑曲霉以香蕉秆作为碳源生产纤维素酶的培养特性。采取30℃培养木霉30 h后接种黑曲霉,32℃混合培养,得到FPA和β-Gluase活性互补的酶系组成:FPA为920.6 U/g,β-Gluase为864.2U/g。对发酵曲降解香蕉秆的研究结果表明:当木霉纯培养曲和黑曲霉纯培养曲以2∶1混合酶解时,最大酶解得率达到30.6%,酶解得率比木霉纯培养曲提高16.8%;优化条件下混合培养的酶解得率为31.5%,达到最大酶解得率所需时间比木霉纯培养曲缩短4 h,酶解得率提高20.2%。混合培养不仅优化了纤维素酶系组成,提高了糖化效率,而且可大大简化生产全酶系纤维素酶的工艺。     

Production and optimization of high grade cellulase from waste date seeds by Cellulomonas uda NCIM 2353 for biohydrogen production

Production of high grade cellulolytic enzymes from waste agricultural biomass would valorise these wastes to valuable products as well as avoid the pollution problems associated with landfilling of the biomass. In the present study, waste date palm (Phoenix dactylifera) seeds were valorised for cellulase production from Cellulomonas uda NCIM 2353 and for its subsequent usage in biohydrogen production. Optimization of key operational parameters such as date seed concentration, xylose, casein and initial media pH were performed using central composite design to obtain the maximum enzyme yield. The optimum values obtained were (g/L): date seed concentration 30.65, xylose concentration 0.55, casein 7.00 and pH 7.40 for a determination coefficient of 0.999. The results demonstrated a higher prediction accuracy of response surface methodology as the cellulase activity increased six fold (175.96 IU/mL) after optimization. The optimum pH and temperature of purified cellulase was 7 and 50 °C respectively where the enzyme retained nearly 80% of activity upto 180 min. Enzymatic hydrolysis studies showed that a high saccharification efficiency of 60.5% was obtained for acid pretreated sugarcane bagasse by the indigenous cellulase, equivalent to the performance of commercial cellulase. Further, the as-obtained reducing sugars were decomposed by Clostridium thermocellum to produce biohydrogen of maximum concentration 187.44 mmol/L at end of 24 h of fermentation. Results show that date seed substrate based cellulase protein can be employed for industrial processes of biohydrogen production.     

Enhanced bio-hydrogen production from cornstalk hydrolysate pretreated by alkaline-enzymolysis with orthogonal design method

Bio-hydrogen (H₂) production from renewable biomass has been accepted as a promising method to produce an alternative fuel for the future. In this study, fermentative hydrogen production from cornstalk (CS) hydrolysate pretreated by alkaline-enzymolysis method was investigated. Meanwhile, a five-factor and five-level orthogonal experimental array was designed to study the influences of Ca(OH)₂ concentration, alkaline hydrolysis time, alkaline hydrolysis temperature, cellulase and xylanase dosages on cornstalk pretreatment and hydrogen production. A maximum reducing sugar yield of 0.59 g/g-CS was obtained at Ca(OH)₂ 0.5%, hydrolysis temperature 115 °C, hydrolysis time 1.5 h, cellulase dosage 4000 U/g-CS and xylanase 4000 U/g-CS. Under this same condition, the maximum hydrogen yields of 168.9 mL/g-CS, 357.6 mL/g-CS, and 424.3 mL/g-CS were obtained at dark-fermentation, photo-fermentation, and two-stage fermentation respectively. It's also found that the significance of these five parameters on H₂ production followed from high to low order as: Ca(OH)₂ concentration, cellulase dosage, xylanase dosage, hydrolysis time, and hydrolysis temperature. By comparing the energy produced with the energy spent, the maximum Energy Sustainability Index (ESI) value of 1.11 was obtained at the two-stage fermentation. The results suggested that two-stage fermentation is a promising and efficient way for hydrogen production from lignocellulosic biomass.     

Enhanced endoglucanase production by soil inhabiting Streptomyces sp. strain NAA9 using lignocellulosic biomass

The actinomycete strain NAA9 exhibiting cellulase production potential was identified based on 16S rDNA sequencing and was found belonging to Streptomyces group. On studying the effect of different lignocellulosic biomass on cellulase production by Streptomyces sp. NAA9, Parthenium hysterophorus weed biomass induced highest levels of enzyme production. The enzyme production was further enhanced by optimization of various parameters, under submerged fermentation conditions. The optimized conditions of 2% (w/v) substrate concentration, 40°C temperature, pH 6.0, an incubation period of 6 days and supplementation of the medium with 0.5% ammonium sulfate, resulted in maximum 0.990±0.012 U/ml endoglucanase production. The findings demonstrate the improved cellulase production by Streptomyces strain NAA9 using P. hysterophorus and indicate the potential of this weed biomass in acting as a low-cost natural substrate for cellulase production. The enzyme produced by actinomycete strain can also be utilized in various applications based on the bioconversion of the cellulosic biomass.     

Enzymatic saccharification of pretreated rice straw by cellulase produced from Bacillus carboniphilus CAS 3 utilizing lignocellulosic wastes through statistical optimization

A marine bacterium, Bacillus carboniphilus CAS 3 was subjected to optimization for cellulase production utilizing cellulosic waste through response surface methodology. Plackett – Burman and Central composite design was employed and the optimal medium constituents for maximum cellulase production (4040.45 U/mL) were determined as rice bran, yeast extract, MgSO₄·7H₂O and KH₂PO₄ at 6.27, 2.52, 0.57 and 0.39 g/L, respectively. The cellulase produced was purified to the specific activity of 434.94 U/mg and 11.46% of recovery with the molecular weight of 56 kDa. The optimum temperature, pH and NaCl for enzyme activity was determined as 50 °C, 9 and 30% and more than 70% of its original activity was retained even at 80 °C, 12 and 35% respectively. Further, enzymatic saccharification of pretreated rice straw yielded about 15.56 g/L of reducing sugar at 96 h, suggesting that the purified cellulase could be useful for production of reducing sugars from cellulosic biomass into ethanol.     

Microbial diversity of hydrogen-producing bacteria in batch reactors fed with cellulose using leachate as inoculum

Hydrogen production using cellulosic residues offers the possibility of waste minimization with renewable energy recovery. In the present study, heat-treated biomass purified from leachate was used as inoculum in batch reactors for hydrogen production fed with different concentrations of cellulose (2.5, 5.0 and 10 g/L), in the presence and absence of exogenous cellulase. The heat-treated biomass did not degrade cellulose and hydrogen production was not detected in the absence of cellulase. In reactors with cellulase, the hydrogen yields were 1.2, 0.6 and 2.3 mol H₂/mol of hydrolyzed cellulose with substrate degradation of 41.4, 28.4 and 44.7% for 2.5, 5.0 and 10 g/L cellulose, respectively. Hydrogen production potentials (P) varied from 19.9 to 125.9 mmol H₂ and maximum hydrogen production rates (R_m) were among 0.8–2.3 mmol H₂/h. The reactor containing 10 g/L of cellulose presented the highest P and R_m among the conditions tested. The main acid produced in reactors were butyric acid, followed by acetic, isobutyric and propionic acids. Bacteria similar to Clostridium sp. (98–99%) were identified in the reactors with cellulase. The heat-treated leachate can be used as an inoculum source for hydrogen production from hydrolyzed cellulose.     

蒸汽爆破预处理玉米芯及其酶解工艺研究

以蒸汽爆破预处理后的玉米芯为原料,进行了玉米芯酶解工艺条件的研究。粉碎后的玉米芯在压力2.8 MPa、保压时间240 s条件下蒸汽爆破预处理,在初始固形物含量为14%(w/v),pH 5.0的条件下,分别添加纤维素酶15 FPA/g(底物)、木聚糖酶225 IU/g(底物),同时添加环境因子MgSO40.005 g/g(底物)、Tween-800.001 g/g(底物),糖化48 h后,还原糖浓度达到71.81 g/L,糖化率达到80.85%。试验结果表明,蒸汽爆破预处理及添加适量环境因子对玉米芯的糖化效果影响显著。     

Thermodynamic analysis of propane dry and steam reforming for synthesis gas or hydrogen production

Thermodynamics was applied to investigate propane dry reforming (DR) and steam reforming (SR). Equilibrium calculations employing the Gibbs free energy minimization were performed upon a wide range of pressure (1–5 atm), temperature (700–1100 K), carbon dioxide to propane ratio (CPR, 1–12) and water to propane ratio (WPR, 1–18). From a thermodynamic perspective, it is demonstrated that DR is promising for production of synthesis gas with low hydrogen content, as opposite to SR which favours generation of synthesis gas with high hydrogen content. Complete conversion of propane was obtained for the range of pressure, temperature, CPR and WPR considered in this study. Atmospheric pressure is shown to be preferable for both DR and SR. Approximately 10 mol of synthesis gas can be produced per mole of propane at a temperature greater than 1000 K from DR when CPR is higher than 6. The optimum conditions for synthesis gas production from DR are found to be 975 K (CPR = 3) for a H₂/CO ratio of 1 and 1100 K (CPR = 1) for a H₂/CO ratio of 2. The greatest CO₂ conversion (95%) can be obtained also at 1100 K and CPR = 1. Preferential conditions for hydrogen production from SR are achieved with the temperatures between 925 and 975 K and WPRs of 12–18. The maximum number of moles of hydrogen produced is 9.1 (925 K and WPR = 18). Under conditions that favour hydrogen production, methane and carbon formation can be eliminated to negligible level.     

Fungal solid-state fermentation and various methods of enhancement in cellulase production

Cellulase serves vast applications in the industries of biofuel, pulp and paper, detergent and textile. With the presence of its three components i.e. endoglucanase, exoglucanase and β-glucosidase, the enzyme can effectively depolymerize the cellulose chains in lignocellulosic substrate to produce smaller sugar units that consist of cellobiose and glucose. Fungi are the most suitable cellulase producers attributing to its ability to produce a complete cellulase system. Solid state fermentation (SSF) by fungi is a preferable production route for cellulase as it imposes lower cost and enables the production of cellulase with higher titre. This article gives an overview on the major aspects of cellulase production via SSF by applying white-rot fungi (WRF) and brown-rot fungi (BRF), which include the type of lignocellulosic substrates for cellulase production, inoculum preparation and process conditions applied in SSF. The parameters that affect SSF production of cellulase such as fermentation medium, duration, pH, temperature and moisture content are highlighted. In addition, potential methods that can improve cellulase production, namely genetic modification, co-culture of different fungal strains, and development of bioreactors are also discussed.