Computer-aided material balancing for prediction of fermentation parameters.

Despite the importance of biomass as a parameter in fermentation processes, there are no commercially available sensors suitable for its measurement. An indirect approach for the assessment of biomass concentration can be based on material balances and on the direct monitoring of fermentation parameters for which there are established sensors (e.g., gaseous oxygen and carbon dioxide). As a consequence, this method requires no assumption of cellular yield coefficients or rate constants. This approach is also readily adaptable to general use since it requires only some knowledge of the compositions of the substrate, cells, and noncellular products.     

Simplified modeling of fed-batch alcoholic fermentation of sugarcane blackstrap molasses

Simplified modeling based on material balances for biomass, ethanol and substrate was used to describe the kinetics of fed-batch alcohol fermentation of sugarcane blackstrap molasses. Maintenance requirements were previously shown to be of particular significance in this system, owing to the use of massive inoculum to minimize inhibitions; therefore, they were taken into consideration for kinetic modeling. Average values of biomass and ethanol yields, productivities, and substrate consumption rates, calculated at the end of runs performed either at constant or exponentially varying flow rates, demonstrated that all of these parameters were influenced by the initial sugar-feeding rate, F(o)S(o). Under conditions of substrate shortage (F(o)S(o) 相似文献   

Infra-red spectroscopic analyses of banana waste degraded by oyster mushroom

Carbon, hydrogen and nitrogen analyses of banana leaf and pseudostem biomass revealed their potentiality as substrates for microorganisms. Infra-red (IR) spectra of both biomass show presence of cellulose, xylan and lignin. IR spectra of leaf and pseudostem biomass degraded in solid state fermentation (SSF) by two Pleurotus species (P. sajor-caju and P. ostreatus) for 40 days showed the utilization of cellulose, xylan and lignin by these microbes. Dynamics of various lignocellulolytic enzymes of Pleurotus species and analyses of carbon, hydrogen and nitrogen contents of degraded biomass supported the same. Both the Pleurotus species exhibited lignin consumption ability on both the substrates.     

Isoprene emission-free poplars--a chance to reduce the impact from poplar plantations on the atmosphere

? Depending on the atmospheric composition, isoprene emissions from plants can have a severe impact on air quality and regional climate. For the plant itself, isoprene can enhance stress tolerance and also interfere with the attraction of herbivores and parasitoids. ? Here, we tested the growth performance and fitness of Populus × canescens in which isoprene emission had been knocked down by RNA interference technology (PcISPS-RNAi plants) for two growing seasons under outdoor conditions. ? Neither the growth nor biomass yield of the PcISPS-RNAi poplars was impaired, and they were even temporarily enhanced compared with control poplars. Modelling of the annual carbon balances revealed a reduced carbon loss of 2.2% of the total gross primary production by the absence of isoprene emission, and a 6.9% enhanced net growth of PcISPS-RNAi poplars. However, the knock down in isoprene emission resulted in reduced susceptibility to fungal infection, whereas the attractiveness for herbivores was enhanced. ? The present study promises potential for the use of non- or low-isoprene-emitting poplars for more sustainable and environmentally friendly biomass production, as reducing isoprene emission will presumably have positive effects on regional climate and air quality.     

基于活细胞量测量的利福霉素发酵过程氮源优化策略

在发酵生产利福霉素SV的过程中,其菌丝体的生长代谢情况及产物发酵合成都与有活力的菌丝量密切相关.介绍了在线活细胞传感仪测定活细胞量的方法,它利用细胞的介电特性,能够排除发酵液中固含物的干扰,测得的电容值与活细胞浓度呈线性相关,可以作为工艺优化过程中的关键参数.通过电容变化反映的前期生长出现的二次生长现象,进行了通过使用迟效氮源豆饼粉代替了原培养基中价格昂贵的速效氮源蛋白胨,成功消除了发酵前期由于氮源利用转换造成的生长停滞期,利用豆饼粉情况下培养前期的OUR和CER达到了14.8和15.3 mmol/L/h,明显高于利用速效氮源蛋白胨A组的8.6和11.3 mmol/L/h,保证了持续较高的比生长速率,对于促进菌体的氧消耗速率的增加和维持有着重要的作用,明显有利于利福霉素的合成与速率的维持,氮源替代组的发酵效价达到了5969±19 U/ml,与对照组(5030±17U/ml)相比显著提升发酵单位18.7%以上.     

Fed-batch fermentation dealing with nitrogen limitation in microbial transglutaminase production by Streptoverticillium mobaraense

In the later stages of a batch fermentation for microbial transglutaminase production by Streptoverticillium mobaraense the availability of a nitrogen source accessible to the microorganism becomes critical. Fed-batch fermentation is investigated with the aim of avoiding this substrate limitation. When peptone is used as a nitrogen source in the feed, no significant improvement of growth and transglutaminase production is observed. This is probably due to crosslinking of the nitrogen source by the transglutaminase produced. Using an inorganic nitrogen source alone does not give satisfactory growth and production. A fed-batch fermentation method has thus been developed to deal with this problem. In the batch phase of the fermentation, an initial medium containing peptone, designed on the basis of the stoichiometric requirements of the microorganism, is used to ensure optimal growth. In the feeding phase, ammonium sulphate is used instead to avoid the crosslinking effect. The feed composition, mainly the amount of nitrogen and carbon source, is also based on the stoichiometric requirements of the organism, taking into account the replacement of peptone by ammonium sulphate. By using this fed-batch fermentation technique, cell-mass dry weight and transglutaminase production could be increased by 33% and 80% respectively, compared to those in a batch fermentation. Received: 10 July 1997 / Received revision: 24 October 1997 / Accepted: 24 October 1997     

Global metabolic profiling of plant cell wall polysaccharide degradation by Saccharophagus degradans

Plant cell wall polysaccharides can be used as the main feedstock for the production of biofuels. Saccharophagus degradans 2–40 is considered to be a potent system for the production of sugars from plant biomass due to its high capability to degrade many complex polysaccharides. To understand the degradation metabolism of plant cell wall polysaccharides by S. degradans, the cell growth, enzyme activity profiles, and the metabolite profiles were analyzed by gas chromatography‐time of flight mass spectrometry using different carbon sources including cellulose, xylan, glucose, and xylose. The specific activity of cellulase was only found to be significantly higher when cellulose was used as the sole carbon source, but the xylanase activity increased when xylan, xylose, or cellulose was used as the carbon source. In addition, principal component analysis of 98 identified metabolites in S. degradans revealed four distinct groups that differed based on the carbon source used. Furthermore, metabolite profiling showed that the use of cellulose or xylan as polysaccharides led to increased abundances of fatty acids, nucleotides and glucuronic acid compared to the use of glucose or xylose. Finally, intermediates in the pentose phosphate pathway seemed to be up‐regulated on xylose or xylan when compared to those on glucose or cellulose. Such metabolic responses of S. degradans under plant cell wall polysaccharides imply that its metabolic system is transformed to more efficiently degrade polysaccharides and conserve energy. This study demonstrates that the gas chromatography‐time of flight mass spectrometry‐based global metabolomics are useful for understanding microbial metabolism and evaluating its fermentation characteristics. Biotechnol. Bioeng. 2010; 105: 477–488. © 2009 Wiley Periodicals, Inc.     

Citric acid production from sucrose by recombinant Yarrowia lipolytica using semicontinuous fermentation

The genetically modified yeast strain Yarrowia lipolytica H222‐S4(p67ICL1)T5 is able to utilize sucrose as a carbon source and to produce citric and isocitric acids in a more advantageous ratio as compared to its wild‐type equivalent. In this study, the effect of pH of the fermentation broth (pH 6.0 and 7.0) and proteose‐peptone addition on citric acid production by the recombinant yeast strain were investigated. It was found that the highest citric acid production occurred at pH 7.0 without any addition of proteose‐peptone. Furthermore, two process strategies (fed‐batch and repeated fed‐batch) were tested for their applicability for use in citric acid production from sucrose by Y. lipolytica. Repeated fed‐batch cultivation was found to be the most effective process strategy: in 3 days of cycle duration, approximately 80 g/L citric acid was produced, the yield was at least 0.57 g/g and the productivity was as much as 1.1 g/Lh. The selectivity of the bioprocess for citric acid was always higher than 90% from the very beginning of the fermentation due to the genetic modification, reaching values of up to 96.4% after 5 days of cycle duration.     

Fast Pyrolysis of Biomass Residues in a Twin-screw Mixing Reactor

Fast pyrolysis is being increasingly applied in commercial plants worldwide. They run exclusively on woody biomass, which has favorable properties for conversion with fast pyrolysis. In order to increase the synergies of food production and the energetic and/or material use of biomass, it is desirable to utilize residues from agricultural production, e.g., straw. The presented method is suitable for converting such a material on an industrial scale. The main features are presented and an example of mass balances from the conversion of several biomass residues is given. After conversion, fractionated condensation is applied in order to retrieve two condensates — an organic-rich and an aqueous-rich one. This design prevents the production of fast pyrolysis bio-oil that exhibits phase separation. A two phase bio-oil is to be expected because of the typically high ash content of straw biomass, which promotes the production of water of reaction during conversion.Both fractionated condensation and the use of biomass with high ash content demand a careful approach for establishing balances. Not all kind of balances are both meaningful and comparable to other results from the literature. Different balancing methods are presented, and the information that can be derived from them is discussed.     

Evaluation of the xylan breakdown potential of eight mesophilic endoxylanases

In biomass degradation using simultaneous saccharification and fermentation (SSF), there is a need for efficient biomass degrading enzymes that can work at lower temperatures suitable for yeast fermentation. As xylan is an important lignocellulosic biomass constituent, this study aimed at investigating the possible differences in xylan breakdown potential of endoxylanases using eight different endoxylanases at conditions relevant for SSF. Both solubilising and degrading capacities of the endoxylanases were investigated using water-insoluble and water-soluble oat spelt xylan as model substrates for biomass xylan. Results showed that selecting for combinations of endoxylanases that are efficient at solubilising xylan on the one hand and degrading it to large extent on the other hand, coupled to high specific activities, seems the best option for complete xylan breakdown in lignocellulosic biomass conversion using SSF.     

Nutritional requirements of mycelial growth of Cordyceps sinensis in submerged culture

AIMS: The nutritional requirements for mycelial growth of Cordyceps sinensis in semi-synthetic liquid media were investigated. The results provide a basis for further physiological study and industrial fermentation of the fungus. METHODS AND RESULTS: Nutritional requirements, including 17 carbohydrates, 16 nitrogen compounds, nine vitamins, four macro-elements, four trace-elements and eight ratios of carbon to nitrogen, were studied for their effects on the mycelial growth in submerged cultures of C. sinensis by using one-factor-at-a-time and orthogonal matrix methods. Among these variables, sucrose, peptone, folic acid, calcium, zinc and a carbon to nitrogen ratio 12 : 1 were identified as the requirements for the optimum mycelial growth. The concentrations of sucrose, peptone and yeast extract were optimized and the effects of medium composition on mycelial growth were found to be in the order sucrose > yeast extract > peptone. The optimal concentration for mycelial growth was determined as 50 g l(-1) sucrose, 10 g l(-1) peptone and 3 g l(-1) yeast extract. CONCLUSIONS: Under optimal culture conditions, over 22 g l(-1) of mycelial biomass could be obtained after 40 days in submerged cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: Cordyceps sinensis, one of the most valued medicinal fungi, is shown to grow in axenic culture. This is the first report on nutritional requirements and design of a simplified semi-synthetic medium for mycelial growth of this psychrophilic species, which grows slowly below 20 degrees C. The results of this study will facilitate research on mass production of the fungus under defined culture conditions.     

Microcalorimetry studies of energy changes during the growth of Klebsiella aerogenes in simple salts/glucose media: growth in phosphate-limited medium

The power-time traces for cells of Klebsiella aerogenes grown in phosphate-limited media were unlike those for cells grown in phosphate-sufficient media. At a phosphate concentration of 18 mumol dm-3 three phases of growth were recognized: the exponential growth phase during which phosphate became exhausted; a slower growth phase to the exhaustion of glucose, and a period of minimal growth when acetate, formed as secondary metabolite, was metabolized. At a concentration of 40 mumol dm-3 only two phases were identified. From the measured values of biomass, carbon dioxide output, glucose and acetate, mass and energy balances were established for each phase of growth and for overall growth. The results are discussed in terms of the energy stored as biomass, that wasted as heat and that required for maintenance and biosynthetic processes when the cells are grown under normal and stressful conditions.     

Application of mass and energy balance regularities in fermentation. Reprinted from Biotechnology and Bioengineering, Vol. XX, No. 10, Pages 1595-1621 (1978)

Material and energy balances for fermentation processes are developed based on the facts that the heat of reaction per electron transferred to oxygen for a wide variety of organic molecules, the number of available electrons per carbon atom in biomass, and the weight fraction carbon in biomass are relatively constant. Mass-energy balance equations are developed which relate the biomass energetic yield coefficient to sets of variables which may be determined experimentally. Organic substrate consumption, biomass production, oxygen consumption, carbon dioxide production, heat evolution, and nitrogen consumption are considered as measured variables. Application of the balances using direct and indirect methods of yield coefficient estimation is illustrated using experimental results from the literature. Product formation is included in the balance equations and the effect of product formation on biomass yield estimates is examined. Application of mass-energy balances in the optimal operation of continuous single-cell protein production facilities is examined, and the variation of optimal operating conditions with changes in yield are illustrated for methanol as organic substrate.     

The behavior of kinetic parameters in production of pectinase and xylanase by solid-state fermentation

Solid-state fermentation (SSF) is defined as the growth of microbes without a free-flowing aqueous phase. The feasibility of using a citrus peel for producing pectinase and xylanase via the SSF process by Aspergillus niger F3 was evaluated in a 2 kg bioreactor. Different aeration conditions were tested to optimize the pectinase and xylanase production. The best air flow intensity was 1 V kg M (volumetric air flow per kilogram of medium), which allowed a sufficient amount of O2 for the microorganism growth producing 265 U/g and 65 U/g pectinases and xylanases, respectively. A mathematical model was applied to determine the different kinetic parameters related to SSF. The specific growth rate and biomass oxygen yield decreased during fermentation, whereas an increase in the maintenance coefficient for the different employed carbon sources was concurrently observed.     

Experimental and theoretical investigations of submerged fermentation and synthesis of pectinolytic enzymes by Aspergillus niger

The growth of the microorganism and the production of the pectinolytic enzyme complex in a stirred 30-l biofermentor using the Aspergillus niger Rehbrücke strain were studied. The time courses of fermentation parameters (formation of biomass, consumption of carbon and inorganic nitrogen source, formation of pectinolytic enzymes) were measured. The formation of biomass showed a distinct lag phase, followed by a log phase with exponential growth and finally a stationary period when cell lysis was beginning. The uptake of the carbon source and inorganic nitrogen source by the A. niger cells corresponded to the time course of growth. The formation of pectinolytic enzymes took place in two steps. The first one was growth-bounded and finished with the end of the log phase of biomass growth. The second step of pectinolytic enzyme formation took place after the end of the catabolite repression of the carbon source and was not growth-bounded. On the basis of the experimental data a mathematical model of the fermentation process was developed. Comparison of the kinetics of the measured fermentation curves and the solution curves of the model showed qualitatively good agreement.     

Application of mass and energy balance regularities in fermentation

Material and energy balances for fermentation processes are developed based on the facts that the heat of reaction per electron transferred to oxygen for a wide variety of organic molecules, the number of available electrons per carbon atom in biomass, and the weight fraction carbon in biomass are relatively constant. Mass–energy balance equations are developed which relate the biomass energetic yield coefficient to sets of variables which may be determined experimentally. Organic substrate consumption, biomass production, oxygen consumption, carbon dioxide production, heat evolution, and nitrogen consumption are considered as measured variables. Application of the balances using direct and indirect methods of yield coefficient estimation is illustrated using experimental results from the literature. Product formation is included in the balance equations and the effect of product formation on biomass yield estimates is examined. Application of mass–energy balances in the optimal operation of continuous single-cell protein production facilities is examined, and the variation of optimal operating conditions with changes in yield are illustrated for methanol as organic substrate.     

Carbon dioxide inhibition of yeast growth in biomass production

Saccharomyces cerevisiae was grown under aerobic and substrate-limiting conditions for efficient biomass production. Under these conditions, where the sugar substrate was fed incrementally, the growth pattern of the yeast cells was found to be uniform, as indicated by a constant respiratory quotient during the entire growing period. The effect of carbon dioxide was investigated by replacing portions of the nitrogen in the air stream with carbon dioxide, while maintaining the oxygen content at the normal 20% level, so that identical oxygen transfer rate and atmospheric pressure were maintained for all experiments with different partial pressures of carbon dioxide. Inhibition of yeast growth was negligible below 20% CO₂ in the aeration mixture. Slight inhibition was noted at the 40% CO₂ level and significant inhibition was noted above the 50% CO₂, level, corresponding to 1.6 × 10^?2M of dissolved CO₂ in the fermentor broth. High carbon dioxide content in the gas phase also inhibited the fermentation activity of baker's yeast.     

Data consistency,yield, maintenance,and hysteresis in batch cultures of Candida lipolytica cultured on n-hexadecane

Candida lipolytica was cultured batchwise using n-hexadecane as the main carbon source. Biomass production, n-hexadecane consumption, oxygen consumption, and carbon dioxide evolution were measured to follow the fermentation. The consistency of the measured data was examined using integrated and instantaneous available electron and carbon balances. Values of the “true” growth yield, η_max, and maintenance coefficient, m_e were estimated using three different sets of data (biomass and n-hexadecane, oxygen and biomass, and CO₂ and biomass), and the results were compared with estimates obtained from literature data. Hysteresis patterns were observed in plots of specific rates of oxygen consumption and carbon dioxide evolution versus specific growth rate.     

Screening of carbon sources for beta-glucosidase production by Aspergillus saccharolyticus

The fungus Aspergillus saccharolyticus was found to produce a culture broth rich in beta-glucosidase activity, an enzyme which plays an essential role for efficient and complete hydrolysis of lignocellulosic biomass. Direct application of fungal fermentation broths produced on-site in a biorefinery may be an integral part of a biorefinery for lowering the cost associated with the use of commercial enzymes for saccharification of biomass. Utilization of low value slip streams from the biorefinery as substrates for such an on-site enzyme production would be ideal to reduce costs. In order to understand which carbon sources that support growth and trigger A. saccharolyticus to produce beta-glucosidases, carbon sources, ranging from monomer sugars to complex lignocellulosic biomasses, including pretreated and hydrolyzed corn stover fractions, were investigated as substrates and inducers of enzyme production. A convenient micro titer plate experimental setup was developed that facilitated a fast screening for beta-glucosidase activity on the different carbon sources. The greatest beta-glucosidase activity was found when A. saccharolyticus was cultivated on media containing xylose, xylan, wheat bran, and pretreated corn stover. In a refinery, beta-glucosidase production by A. saccharolyticus could with success be based on the biomass hemicelluloses and their degradation products which cannot be converted by conventional yeast.     

A bioenergetic model of a mixed production fermentation

A bioenergetic model has been developed for the fermentation of glucose by Bacillus polymyxa. This model uses energy balances to determine which pathways are utilized by the substrate. The model can predict substrate consumption, biomass formation, and the product distribution for this fermentation. The products are carbon dioxide, water, 2,3-butanediol, and ethanol, where ethanol represents lumped anaerobic products.