Selma Ates

Investigation of extractive citric acid fermentation using response-surface methodology

Extractive citric acid fermentation with Aspergillus niger microoganism was investigated in the presence of corn oil and Hostarex A327 in oleyl alcohol. In the extractive fermentation, production and separation phases are achieved simultaneously. Before Response Surface Methodology (RSM) was applied,the effect of potassium ferrocyanide (K4Fe(CN)6) concentration on citric acid production and the prevention of solvent toxicity using corn oil were investigated. Citric acid concentration increased with increasing K4Fe(CN)6 concentration. Solvent toxicity was reduced using corn oil in the extractive citric fermentation. In the RSM, the potassium ferrocyanide concentration, (0.02–0.10%, w/v), the ratio of organic phase volume to the aqueous phase volume, Vor/Vaq, (0.5–1.5), the corn oil concentration (0–20%, by volume) and the Hostarex A327 content in oleyl alcohol (10–50%, by volume) were the critical components. Optimum citric acid concentration was obtained as 5.70 g/l with employing the following predicted optimum extraction conditions: K4Fe(CN)6 of 0.06% (w/v), Vor/Vaq of 1.25, corn oil concentration of 13.7% (by volume) and Hostarex A327 content in oleyl alcohol of 33% (by volume). Citric acid production by extractive fermentation was increased approximately 40% with respect to the control run (4.10 g/l).

A new method for immobilization of β-galactosidase and its utilization in a plug flow reactor

Abstract A new method for the immobilization of β-galactosidase was developed which involved entrapment of the enzyme in cobalt alginate beads with a relative activity of 83%, the highest activity reported in the literature for β-galactosidase immobilization. Enzyme leakage was avoided by treatment with glutaraldehyde solution (1%) following which the relative activity (83%) was stable. The effect of pH and temperature on enzyme activity and reusability were investigated. This method yielded high activity and good physico-chemical characteristics and the immobilized particles were used in a plug flow reactor. The effects of the residence time and substrate concentration on productivity were investigated. The effect of temperature on operating time was also studied. This method could potentially be applied to be a general system for immobilization of different enzymes which are not inactivated by cobalt salts.

Enhancement of citric acid production by immobilized and freely suspended Aspergillus niger using silicone oil

Abstract The use of silicone oil as an oxygen vector for increasing citric acid production by free and immobilized Aspergillus niger conidiospores was studied. When silicone oil was used, citric acid concentration increased with respect to the control run in free and immobilized systems 2.0 and 1.6 times, respectively. The effect of potassium ferrocyanide [K 4 Fe(CN) 6 ] on citric acid production in a medium containing air, oxygen and silicone oil was studied. When K 4 Fe(CN) 6 was used with oxygen and silicone oil, citric acid concentration decreased significantly because of the conversion of ferrocyanide to ferricyanide. The reuse of immobilized A. niger conidiospores was investigated in citric acid production medium containing 2% (v/v) silicone oil. Citric acid production decreased on increasing the reuse number.

Production of actinorhodin by Streptomyces coelicolor in batch and fed-batch cultures

Abstract Fed-batch fermentations of Streptomyces coelicolor in chemically defined medium in a 20 litre bioreactor were used to produce actinorhodin. Concentrated solutions of phosphate and nitrate with or without glucose were fed intermittently or continuously. Continuous feeding of glucose alone was found to be the best strategy for actinorhodin production. In this case, the specific productivity was almost twice that obtained in conventional batch fermentation.

OXYGEN DIFFUSIVITY IN CALCIUM ALGINATE GEL BEADS CONTAINING GLUCONOBACTER SUBOXYDANS

Gaining insight into the mass transfer characteristics in immobilized enzyme and microorganism systems bears much importance because of their widely increased use in industrial scale production as well as for analysis purposes. In this study, the effective diffusion coefficient of oxygen in calcium alginate gel with and without cells has been determined by the Moment Analysis Method for the first time in literature. When the gel concentration was increased from 1 to 3 %, De values of oxygen varied between 2.54 x 10(-5) cm2/s and 2.58 x 10(-5) cm2/s indicating almost no dependency on gel concentration. However, a decrease in effective diffusion coefficient (from 2.55 cm2/s to 2.47 cm2/s) was observed with increased immobilized Gluconobacter suboxydans concentration in the range of 0 to 6 %. Experimental results on liquid-particle mass transfer coefficient revealed a negligible external mass transfer resistance. Effectiveness factor for the bioreactor system was also calculated and found to be 0.39 and 0.21 for gel beads of 0.1 and 0.2 cm radius respectively. It is concluded therefore that the use of smaller gel beads could substantially improve the production efficiency in similar bioreactors.

Synthesis of N,N-dimethylamines via barbier -grignard -type electrophilic amination

Abstract Aryl Grignard reagents react with N,N‐dimethyl O‐(mesitylenesulfonyl)hydroxylamine in THF under Barbier conditions at room temperature and give N,N‐dimethylanilines with high yields in a 2‐h reaction. The amination yield of in situ Grignard reagents were not lower than those of preformed aryl Grignard reagents. In situ cycloalkyl‐, allyl‐, and benzylmagnesium bromides did not react with N,N‐dimethyl O‐(mesitylenesulfonyl)hydroxylamine, except that amination of in situ n‐hexylmagnesium bromide resulted in a medium yield. Grignard–Barbier‐type amination of aryl bromides with N,N‐dimethyl O‐(mesitylenesulfonyl)hydroxylamine provides a new alternative route for the synthesis of N,N‐dimethylanilines.

Properties of immobilized glucose oxidase and enhancement of enzyme activity

Abstract In this study; glucose oxidase (GOD) and MnO2 were immobilized in alginate gel beads using the entrapment method and effects of oxygen vectors on immobilized GOD activity were investigated. The specific activity of free enzyme was 1.3 units/mg protein whereas that of immobilized enzyme was 8.4 × 10−1 units/mg protein. The Km values for free and immobilized enzyme were found to be 2.7 mM, 2.9 mM; Vmax values 3.64 × 10−1 μmol/min.mL, 2.61 × 10−1 μmol/min.mL, respectively. When 4% (v/v) silicone oil or soybean oil was used, the activity of immobilized GOD increased 1.7 times and 1.3 times, respectively, compared to media without these oils.

Enhanced ethyl butyrate production using immobilized lipase

Abstract In this study, the production of ethyl butyrate was investigated by using immobilized lipase enzyme in shake flasks. In order to determine optimum conditions for the production, response surface methodology was used. The model indicated the optimum conditions for maximum conversion (9.1%) at the 0.31 M substrate concentration, acid- alcohol molar ratio of 0.49, immobilized enzyme 25% (w/v) at 35°C, for 3 hours which were in good agreement with the experimental value. At the end of the 55 hours conversion was obtained as 61.3%. When Na2HPO4 was used in reaction medium conversion increased to 90.3% for 55 hours.

Properties of Immobilized Pectinesterase on Nylon

Abstract Pectinesterase (PE) was immobilized by covalent attachment on nylon-polyethylenimine co-polymer and the properties of the immobilized enzyme was investigated. The nylon support was activated both by using dimethyl sulphate (DMS) and triethyloxonium tetrafluoroborate (TOTFB). The suitable conditions for an operative and stable system were investigated. The immobilization of PE on nylon which had been by polyethylenimine (PEI) resulted in some loss of activity because of steric hindrance of pectin. The activity immobilization yielded 8.2% for DMS and 12.7% for TOTFB and higher than the previously reported in the literature. The pH optima and temperature stability of the immobilized PE significantly increased.

EXTRACTIVE FERMENTATION OF GIBBERELLIC ACID WITH FREE AND IMMOBILIZED Gibberella fujikuroi

Gibberelic acid fermentation using extractive methods was carried out in the presence of corn oil and Alamine 336. Gibberella fujikuroi fungus (NRRL 2278) was used to produce gibberellic acid. Oleyl alcohol was a diluting agent for Alamine 336. The effects of oleyl alcohol (100%, v/v), corn oil (5–25%, v/v), the concentration of Alamine 336 in oleyl alcohol, and feeding air were examined in this study. According to the results, oleyl alcohol was not effective on the production. On the other hand, oleyl alcohol solutions containing 15–30% (v/v) Alamine 336 showed effects as a toxic substance. In order to reduce solvent toxicity, corn oil was used. Addition of corn oil increased the concentration of gibberellic acid 1.3-fold compared to the control. Then the effects of immobilization and co-immobilization on extractive gibberelic acid fermentation were investigated. The highest total gibberellic acid concentration of 158.9 mg/L was produced with immobilized cells and feeding air by using extractive fermentation. The yield of gibberellic acid increased about 2.6-fold compared with the shake-flask fermentation (60.5 mg/L) without organic solutions.