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1.
Comparison of macauba and soybean oils as substrates for the enzymatic biodiesel production in ultrasound-assisted system.
Santin, CMT, Michelin, S, Scherer, RP, Valério, A, Luccio, MD, Oliveira, D, Oliveira, JV
Ultrasonics sonochemistry. 2017;(Pt A):525-528
Abstract
The objective of this study is to evaluate the batch enzymatic production of biodiesel in solvent-free system under ultrasound using as substrates ethanol, soybean oil and macauba fruit oil. For this purpose, a Plackett & Burman experimental design was carried out for soybean oil while a 24-1 design was conducted for macauba oil in order to maximize the biodiesel conversion for each system. Good conversions to fatty acid ethyl esters (FAEE), 88% for soybean oil and 75.2% for macauba oil, was obtained thus demonstrating the potential use of ultrasound for this reaction system.
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2.
Comparison of operating strategies for increased biogas production from thin stillage.
Moestedt, J, Nordell, E, Schnürer, A
Journal of biotechnology. 2014;:22-30
Abstract
The effect of increasing organic loading rate (OLR) and simultaneously decreasing hydraulic retention time (HRT) during anaerobic digestion of sulphur- and nitrogen-rich thin stillage was investigated during operation of continuously stirred tank laboratory reactors at two different temperatures. The operating strategies and substrate were set in order to mimic an existing full-scale commercial biogas plant in Sweden. The reactors were operated for 554-570 days with a substrate mixture of thin stillage and milled grain, resulting in high ammonium concentrations (>4.5gL(-1)). Initially, one reactor was operated at 38°C, as in the full-scale plant, while in the experimental reactor the temperature was raised to 44°C. Both reactors were then subjected to increasing OLR (from 3.2 to 6.0gVSL(-1)d(-1)) and simultaneously decreasing HRT (from 45 to 24 days) to evaluate the effects of these operational strategies on process stability, hydrogen sulphide levels and microbial composition. The results showed that operation at 44°C was the most successful strategy, resulting in up to 22% higher methane yield compared with the mesophilic reactor, despite higher free ammonia concentration. Furthermore, kinetic studies revealed higher biogas production rate at 44°C compared with 38°C, while the level of hydrogen sulphide was not affected. Quantitative PCR analysis of the microbiological population showed that methanogenic archaea and syntrophic acetate-oxidising bacteria had responded to the new process temperature while sulphate-reducing bacteria were only marginally affected by the temperature-change.
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3.
Optimization of process parameters for the production of tyrosine phenol lyase by Citrobacterfreundii MTCC 2424.
Chandel, M, Azmi, W
Bioresource technology. 2009;(5):1840-6
Abstract
The process optimization using technological combinations for the production of tyrosine phenol lyase by Citrobacter freundii MTCC 2424 has been carried out in this study. The maximum production of tyrosine phenol lyase (0.15 U) was obtained by culturing C. freundii MTCC 2424 in a medium containing (g/l) meat extract 5.0, yeast extract 5.0, peptone 2.5, and l-tyrosine 1.0 at 25 degrees C for 16 h in a temperature controlled orbital shaker. A 2.5-fold increase in enzyme activity with 1.3-fold decrease in the cost of enzyme production (in terms of media components) was achieved by using different technological combinations. The process optimization using technological combinations allowed quick optimization of large number of variables, which helps in designing of suitable fermentation conditions for the cost-effective production of tyrosine phenol lyase. Moreover, this also provides information for balancing the nutrient concentration with minimum experimentation.
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4.
Comparative study on chemical pretreatment methods for improving enzymatic digestibility of crofton weed stem.
Zhao, X, Zhang, L, Liu, D
Bioresource technology. 2008;(9):3729-36
Abstract
In order to utilize and control the invasive weed, crofton weed (Eupatorium adenophorum Spreng), a potential pathway was proposed by using it as a feedstock for production of fermentable sugars. Three chemical pretreatment methods were used for improving enzymatic saccharification of the weed stem. Mild H2SO4 pretreatment could obtain a relatively high yield of sugars in the pretreatment (32.89%, based on initial holocellulose), however, it led to only a slight enhancement of enzymatic digestibility. NaOH pretreatment could obtain a higher enzymatic conversion ratio of cellulose compared with H2SO4 pretreatment. Peracetic acid (PAA) pretreatment seemed to be the most effective for improving enzymatic saccharification of the weed stem in the three chemical pretreatment methods under the same conditions. The conversion ratio of cellulose in the sample pretreated by PAA under the "optimal" condition was increased to 50% by cellulase loading of 80 FPU/g cellulose for 72 h incubation. A number of empirical quadratic models were successfully developed according to the experimental data to predict the yield of sugar and degree of delignification.
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5.
Role of energetic coenzyme pools in the production of L-carnitine by Escherichia coli.
Cánovas, M, Sevilla, A, Bernal, V, Leal, R, Iborra, JL
Metabolic engineering. 2006;(6):603-18
Abstract
The aim of this work was to understand the steps controlling the biotransformation of trimethylammonium compounds into L(-)-carnitine by Escherichia coli. The high-cell density reactor steady-state levels of carbon source (glycerol), biotransformation substrate (crotonobetaine), acetate (anaerobiosis product) and fumarate (as an electron acceptor) were pulsed by increasing them fivefold. Following the pulse, the evolution of the enzyme activities involved in the biotransformation process of crotonobetaine into L(-)-carnitine (crotonobetaine hydration), in the synthesis of acetyl-CoA (ACS: acetyl-CoA synthetase and PTA: ATP: acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid (ICDH: isocitrate dehydrogenase) and glyoxylate (ICL: isocitrate lyase) cycles was monitored. In addition, the levels of carnitine, the cell ATP content and the NADH/NAD(+) ratio were measured in order to assess the importance and participation of these energetic coenzymes in the catabolic system. The results provided an experimental demonstration of the important role of the glyoxylate shunt during biotransformation and the need for high levels of ATP to maintain metabolite transport and biotransformation. Moreover, the results obtained for the NADH/NAD(+) pool indicated that it is correlated with the biotransformation process at the NAD(+) regeneration and ATP production level in anaerobiosis. More importantly, a linear correlation between the NADH/NAD(+) ratio and the levels of the ICDH and ICL (carbon and electron flows) and the PTA and ACS (acetate and ATP production and acetyl-CoA synthesis) activity levels was assessed. The main metabolic pathway operating during cell metabolic perturbation with a pulse of glycerol and acetate in the high-cell density membrane reactor was that related to ICDH and ICL, both regulating the carbon metabolism, together with PTA and ACS enzymes (regulating ATP production).
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6.
The use of microorganisms in L-ascorbic acid production.
Bremus, C, Herrmann, U, Bringer-Meyer, S, Sahm, H
Journal of biotechnology. 2006;(1):196-205
Abstract
L-Ascorbic acid has been industrially produced for around 70 years. Over the past two decades, several innovative bioconversion systems have been proposed in order to simplify the long time market-dominating Reichstein method, a largely chemical synthesis by which still a considerable part of L-ascorbic acid is produced. Here, we describe the current state of biotechnological alternatives using bacteria, yeasts, and microalgae. We also discuss the potential for direct production of l-ascorbic acid exploiting novel bacterial pathways. The advantages of these novel approaches competing with current chemical and biotechnological processes are outlined.
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7.
Biosafety considerations for selectable and scorable markers used in cassava (Manihot esculenta Crantz) biotechnology.
Petersen, W, Umbeck, P, Hokanson, K, Halsey, M
Environmental biosafety research. 2005;(2):89-102
Abstract
Cassava is an important subsistence crop grown only in the tropics, and represents a major source of calories for many people in developing countries. Improvements in the areas of resistance to insects and viral diseases, enhanced nutritional qualities, reduced cyanogenic content and modified starch characteristics are urgently needed. Traditional breeding is hampered by the nature of the crop, which has a high degree of heterozygosity, irregular flowering, and poor seed set. Biotechnology has the potential to enhance crop improvement efforts, and genetic engineering techniques for cassava have thus been developed over the past decade. Selectable and scorable markers are critical to efficient transformation technology, and must be evaluated for biosafety, as well as efficiency and cost-effectiveness. In order to facilitate research planning and regulatory submission, the literature on biosafety aspects of the selectable and scorable markers currently used in cassava biotechnology is surveyed. The source, mode of action and current use of each marker gene is described. The potential for toxicity, allergenicity, pleiotropic effects, horizontal gene transfer, and the impact of these on food or feed safety and environmental safety is evaluated. Based on extensive information, the selectable marker genes nptII, hpt, bar/pat, and manA, and the scorable marker gene uidA, all have little risk in terms of biosafety. These appear to represent the safest options for use in cassava biotechnology available at this time.
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8.
Biotechnological production of 2-phenylethanol.
Etschmann, MM, Bluemke, W, Sell, D, Schrader, J
Applied microbiology and biotechnology. 2002;(1):1-8
Abstract
2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.