Biomedical subjects

Kati Réczey

Publications and source records attributed to Kati Réczey.

9 recordsLinked to original sources

PubMed2005

beta-Glucosidase production by Trichoderma reesei.

The hydrolysis of cellulose to the water-soluble products cellobiose and glucose is achieved via synergistic action of cellulolytic proteins. The three types of enzymes involved in this process are endoglucanases, cellobiohydrolases, and beta-glucosidases. One of the best fungal cellulase producers is Trichoderma reesei RUT C30. However, the amount of beta-glucosidases secreted by this fungus is insufficient for effective cellulose conversion. We investigated the production of cellulases and beta-glucosidases in shake-flask cultures by applying three pH-controlling strategies: the pH of the production medium was adjusted to 5.8 after the addition of seed culture with no additional pH adjustment performed, the pH was adjusted to 6.0 daily, and the pH was maintained at 6.0 by the addition of Tris-maleate buffer to the growth medium. Different carbon sources Solka Floc 200, glucose, lactose, and sorbitol were added to standard Mandels nutrients. The lowest beta-glucosidase activities were obtained when no pH adjustment was done regardless of the carbon source employed. Somewhat higher levels of beta- glucosidase were measured in the culture filtrates when daily pH adjustment was carried out. The effect of buffering the culture medium on beta-glucosidase liberation was most prominent when a carbon source inducing the production of other cellulases was applied.

Cell Culture Techniques↗

PubMed2004

High solid simultaneous saccharification and fermentation of wet oxidized corn stover to ethanol.

In this study ethanol was produced from corn stover pretreated by alkaline and acidic wet oxidation (WO) (195 degrees C, 15 min, 12 bar oxygen) followed by nonisothermal simultaneous saccharification and fermentation (SSF). In the first step of the SSF, small amounts of cellulases were added at 50 degrees C, the optimal temperature of enzymes, in order to obtain better mixing condition due to some liquefaction. In the second step more cellulases were added in combination with dried baker's yeast (Saccharomyces cerevisiae) at 30 degrees C. The phenols (0.4-0.5 g/L) and carboxylic acids (4.6-5.9 g/L) were present in the hemicellulose rich hydrolyzate at subinhibitory levels, thus no detoxification was needed prior to SSF of the whole slurry. Based on the cellulose available in the WO corn stover 83% of the theoretical ethanol yield was obtained under optimized SSF conditions. This was achieved with a substrate concentration of 12% dry matter (DM) acidic WO corn stover at 30 FPU/g DM (43.5 FPU/g cellulose) enzyme loading. Even with 20 and 15 FPU/g DM (corresponding to 29 and 22 FPU/g cellulose) enzyme loading, ethanol yields of 76 and 73%, respectively, were obtained. After 120 h of SSF the highest ethanol concentration of 52 g/L (6 vol.%) was achieved, which exceeds the technical and economical limit of the industrial-scale alcohol distillation. The SSF results showed that the cellulose in pretreated corn stover can be efficiently fermented to ethanol with up to 15% DM concentration. A further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. It was also shown that the fermentation could be followed with an easy monitoring system based on the weight loss of the produced CO2.

Bioreactors↗

PubMed2004

Dynamics of cellulase production by glucose grown cultures of Trichoderma reesei Rut-C30 as a response to addition of cellulose.

An economic process for the enzymatic hydrolysis of cellulose would allow utilization of cellulosic biomass for the production of easily fermentable low-cost sugars. New and more efficient fermentation processes are emerging to convert this biologic currency to a variety of commodity products with a special emphasis on fuel ethanol production. Since the cost of cellulase production currently accounts for a large fraction of the estimated total production costs of bioethanol, a significantly less expensive process for cellulase enzyme production is needed. It will most likely be desirable to obtain cellulase production on different carbon sources-including both polymeric carbohydrates and monosaccharides. The relation between enzyme production and growth profile of the microorganism is key for designing such processes. We conducted a careful characterization of growth and cellulase production by the soft-rot fungus Trichoderma reesei. Glucose-grown cultures of T. reesei Rut-C30 were subjected to pulse additions of Solka-floc (delignified pine pulp), and the response was monitored in terms of CO2 evolution and increased enzyme activity. There was an immediate and unexpectedly strong CO2 evolution at the point of Solka-floc addition. The time profiles of induction of cellulase activity, cellulose degradation, and CO2 evolution are analyzed and discussed herein.

Biomass↗

PubMed2004

Effect of pH on cellulase production of Trichoderma reesei RUT C30.

Currently, the high market price of cellulases prohibits commercialization of the lignocellulosics-to-fuel ethanol process, which utilizes enzymes for saccharification of cellulose. For this reason research aimed at understanding and improving cellulase production is still a hot topic in cellulase research. Trichoderma reesei RUT C30 is known to be one of the best hyper producing cellulolytic fungi, which makes it an ideal test organism for research. New findings could be adopted for industrial strains in the hope of improving enzyme yields, which in turn may result in lower market price of cellulases, thus making fuel ethanol more cost competitive with fossil fuels. Being one of the factors affecting the growth and cellulase production of T. reesei, the pH of cultivation is of major interest. In the present work, numerous pH-controlling strategies were compared both in shake-flask cultures and in a fermentor. Application of various buffer systems in shake-flask experiments was also tested. Although application of buffers resulted in slightly lower cellulase activity than that obtained in non-buffered medium, beta-glucosidase production was increased greatly.

Biotechnology↗

PubMed2004

Yields from glucose, xylose, and paper sludge hydrolysate during hydrogen production by the extreme thermophile Caldicellulosiruptor saccharolyticus.

This study addressed the utilization of an industrial waste stream, paper sludge, as a renewable cheap feedstock for the fermentative production of hydrogen by the extreme thermophile Caldicellulosiruptor saccharolyticus. Hydrogen, acetate, and lactate were produced in medium in which paper sludge hydrolysate was added as the sole carbon and energy source and in control medium with the same concentration of analytical grade glucose and xylose. The hydrogen yield was dependent on lactate formation and varied between 50 and 94% of the theoretical maximum. The carbon balance in the medium with glucose and xylose was virtually 100%. The carbon balance was not complete in the paper sludge medium because the measurement of biomass was impaired owing to interfering components in the paper sludge hydrolysate. Nevertheless, >85% of the carbon could be accounted for in the products acetate and lactate. The maximal volumetric hydrogen production rate was 5 to 6 mmol/(L x h), which was lower than the production rate in media with glucose, xylose, or a combination of these sugars (9-11 mmol/[L x h]). The reduced hydrogen production rate suggests the presence of inhibiting components in paper sludge hydrolysate.

Bacteria↗

PubMed2004

Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility.

Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million t of corn stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40% of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time, and pH during steam pretreatment. The best conditions (200 degrees C, 5 min, 2% H2SO4) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated material. However, steam pretreatment at 190 degrees C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars, 56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the glucose to ethanol efficiently.

Biotechnology↗

PubMed2003

Pretreatment of corn stover using wet oxidation to enhance enzymatic digestibility.

Corn stover is an abundant, promising raw material for fuel ethanol production. Although it has a high cellulose content, without pretreatment it resists enzymatic hydrolysis, like most lignocellulosic materials. Wet oxidation (water, oxygen, mild alkali or acid, elevated temperature and pressure) was investigated to enhance the enzymatic digestibility of corn stover. Six different combinations of reaction temperature, time, and pH were applied. The best conditions (60 g/L of corn stover, 195 degrees C, 15 min, 12 bar O2, 2 g/L of Na2CO3) increased the enzymatic conversion of corn stover four times, compared to untreated material. Under these conditions 60% of hemicellulose and 30% of lignin were solubilized, whereas 90% of cellulose remained in the solid fraction. After 24-h hydrolysis at 50 degrees C using 25 filter paper units (FPU)/g of drymatter (DM) biomass, the achieved conversion of cellulose to glucose was about 85%. Decreasing the hydrolysis temperature to 40 degrees C increased hydrolysis time from 24 to 72 h. Decreasing the enzyme loading to 5 FPU/g of DM biomass slightly decreased the enzymatic conversion from 83.4 to 71%. Thus, enzyme loading can be reduced without significantly affecting the efficiency of hydrolysis, an important economical aspect.

Cellulase↗

PubMed2003

Hydrogen production from paper sludge hydrolysate.

The main objective of this study was to develop a system for the production of "renewable" hydrogen. Paper sludge is a solid industrial waste yielding mainly cellulose, which can be used, after hydrolysis, as a feedstock in anaerobic fermentation by (hyper)thermophilic organisms, such as Thermotoga elfii and Caldicellulosiruptor saccharolyticus. Tests on different medium compositions showed that both bacteria were able to produce hydrogen from paper sludge hydrolysate, but the amount of produced hydrogen and the requirement for other components differed. Hydrogen production by T. elfii strongly depended on the presence of yeast extract and salts. By contrast, C. saccharolyticus was less dependent on medium components but seemed to be inhibited by a component present in the sludge hydrolysate. Utilization of xylose was preferred over glucose by C. saccharolyticus.

Bacteria↗

PubMed2002

Chemical pretreatments of corn stover for enhancing enzymatic digestibility.

Corn stover, the most abundant agricultural residue in Hungary, is a potential raw material for the production of fuel ethanol as a result of its high content of carbohydrates, but a pretreatment is required for its efficient hydrolysis. In this article, we describe the results using various chemicals such as dilute H2SO4, HCl, and NaOH separately as well as consecutively under relative mild conditions (120 degrees C, 1 h). Pretreatment with 5% H2SO4 or 5% HCl solubilized 85% of the hemicellulose fraction, but the enzymatic conversion of pretreated materials increased only two times compared to the untreated corn stover. Applying acidic pretreatment following a 1-d soaking in base achieved enzymatic conversion that was nearly the theoretical maximum (95.7%). Pretreatment with 10% NaOH decreased the lignin fraction >95%, increased the enzymatic conversion more than four times, and gave a 79.4% enzymatic conversion. However, by increasing the reaction time, the enzymatic degradability could also be increased significantly, using a less concentrated base. When the time of pretreatment was increased three times (0.5% NaOH at 120 degrees C), the amount of total released sugars was 47.9 g from 100 g (dry matter) of untreated corn stover.

Cellulase↗