Yoon Seok Song

Biodiesel production by a mixture of Candida rugosa and Rhizopus oryzae lipases using a supercritical carbon dioxide process

In this study, various factors, such as temperature, pressure, agitation speed, water content, and the concentration and ratio of immobilized ROL and CRL were investigated for the efficient enzymatic production of biodiesel using a supercritical carbon dioxide process. Furthermore, a stepwise reaction method for the maintenance of immobilized lipase activity was optimized. Optimal conditions for biodiesel production were determined to be as follows: 130 bar pressure, 45 °C temperature, 250 rpm agitation speed, 10% water content, and 20% immobilized ROL and CRL (1:1). When batch process was performed under optimal conditions, the biodiesel conversion yield was 99.13% at 3 h. Biodiesel conversion yield was 99.99% at 2 h when 90 mmol methanol was used in a stepwise reaction. Moreover, the conversion yield of biodiesel produced by the repeated recycling of immobilized lipase in the stepwise reactions was 85% after 20 reuses.

Enzymatic fuel cells based on electrodeposited graphite oxide/cobalt hydroxide/chitosan composite–enzymeelectrode

Enzymatic fuel cells (EFCs) use redox enzymes with high electron transfer rates that lead to high power density from bioavailable substrates. However, EFCs are limited by the difficult electrical wiring of the enzymes to the electrode. Therefore, deposition of Co(OH)₂ onto graphite oxide (GO) was improved for efficient wiring of the enzymes. The GO/Co(OH)₂/chitosan composites were electrodeposited for immobilization of glucose oxidase (GOD) or laccase on an Au electrode, respectively. The electrical properties of the bioelectrode according to cyclic voltammetry were improved using GO/Co(OH)₂/chitosan composites. The anode and cathode system was composed of GOD and laccase as biocatalysts and glucose/oxygen as substrates under ambient conditions (pH 7.0 and 25 °C). The EFC using GO/Co(OH)₂/chitosan composites with a mediator delivered a high power density of up to 517±3.3 μW/cm² at 0.46 V and open circuit voltage of 0.60 V. These results provide a promising direction for further development and application of EFCs.

Batch and continuous synthesis of lactulose from whey lactose by immobilized β-galactosidase.

In this study, lactulose synthesis from whey lactose was investigated in batch and continuous systems using immobilized β-galactosidase. In the batch system, the optimal concentration of fructose for lactulose synthesis was 20%, and the effect of galactose, glucose and fructose on β-galactosidase activity was determined for hydrolysis of whey lactose and the transgalactosylation reaction for lactulose synthesis. Galactose and fructose were competitive inhibitors, and glucose acted as a noncompetitive inhibitor. The inhibitory effects of galactose and glucose were stronger in the transgalactosylation reaction than they were in the hydrolysis reaction. In addition, when immobilized β-galactosidase was reused for lactulose synthesis, its catalytic activity was retained to the extent of 52.9% after 10 reuses. Lactulose was synthesized continuously in a packed-bed reactor. We synthesized 19.1g/l lactulose during the continuous flow reaction at a flow rate of 0.5 ml/min.

Quantitative Detection of Glyphosate by Simultaneous Analysis of UV Spectroscopy and Fluorescence Using DNA-Labeled Gold Nanoparticles

A sandwich-type immunosensor composed of antigen-double target/probe DNA-coated gold nanoparticles (NPs) was developed for the measurement of fluorescence intensity and quantitative analysis of single-stranded DNA based on the concentration of free glyphosate. The reaction between the antigen-double DNA-gold NPs and immobilized antibody on the substrate was carried out for 2 h. The results of the antigen-antibody reaction were measured on the basis of the fluorescence intensity obtained from comparison with the free antigens at concentrations of 0.01-100 μg mL(-1) for the detection of immobilized antigen-double DNA-gold NPs. For the quantitative analysis based on the concentration of glyphosate(0.01-100 μg mL(-1)), the immunosensor response also revealed the same detection range of glyphosate using DNA detection.

Statistical optimization of medium components for the production of xylanase byAspergillus niger KK2 in submerged cultivation

Medium composition was optimized for the production of xylanase byAspergillus niger KK2 using statistical experimental designs. Corn steep liquor (CSL) and industrial yeast extract (IYE) were the most important factors affecting xylanase activity. The medium that produced the optimum conditions for the production of xylanase contained 3% rice straw, 1% wheat bran, 6.3% CSL, 0.15% IYE, and 0.5% KH2PO4. After 4 days of cultivation under optimized conditions in a 2.5-L stirred tank reactor the activity and productivity of xylanase were 620 IU/mL and 6,458 IU/L.h, respectively. The highest xylanase activity obtained using the optimized medium was 80% greater than the activity obtained using basal medium. The xylanase activity predicted by a polynomial model was 670 IU/ml.

Improvement of lactulose synthesis through optimization of reaction conditions with immobilized β-galactosidase

Kluyveromyces lactisβ-galactosidase was immobilized on silica gels using a covalent bonding method. To improve lactulose synthesis using immobilized β-galactosidase, the optimal reaction conditions, such as lactose and fructose concentrations, pH and ionic strength of the buffer, loading amount of the enzyme and temperature, were determined. Lactulose synthesis using the immobilized β-galactosidase was markedly improved after optimization of the reaction conditions. When the lactulose synthesis was carried out at 47 °C using 40% (w/v) lactose, 20% (w/v) fructose and immobilized β-galactosidase of 12 U/ml in 50 mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 15.80 g/l and 1.32 mg/U·h, respectively. In addition, when the immobilized β-galactosidase was reused for lactulose synthesis, its catalytic activity retained 60.5% after 10 reuses.

Optimization of lactulose synthesis from whey lactose by immobilized β-galactosidase and glucose isomerase.

In the present study, commercially available whey was used as a lactose source, and immobilized β-galactosidase and glucose isomerase were used to synthesize lactulose from whey lactose in the absence of fructose. Optimal reaction conditions, such as lactose concentration, temperature, ionic strength of the buffer, and ratio of immobilized enzymes, were determined to improve lactulose synthesis using immobilized enzymes. Lactulose synthesis using immobilized enzymes improved markedly after optimizing the reaction conditions. When the lactulose synthesis was carried out at 53.5°C using 20% (w/v) whey lactose, 12U/ml of immobilized β-galactosidase and 60U/ml of immobilized glucose isomerase in 100mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 7.68g/l and 0.32mg/Uh, respectively. Additionally, when the immobilized enzymes were reused for lactulose synthesis, their catalytic activity was 57.1% after 7 repeated uses.

Bioconversion of Linoleic Acid to Conjugated Linoleic Acid by Bifidobacterium breve

The bioconversion of linoleic acid (LA) to conjugated linoleic acid (CLA) was investigated to examine LA-adaptation ofBifidobacterium breve KCTC 3461 to additions of 1 to 5 mg/mL of LA overtime. To induce LA-adaptation,B. breve KCTC 3461 was treated with LA, according to three schemes. For LA-adaptedB. breve the maximum concentration of CLA, 300–350 μg/mL, was obtained in cys-MRS medium containing 1 mg/mL of LA. The CLA production significantly increased with increasing LA concentration, from 1 to 4 mg/mL, but the conversion of LA to CLA gradually decreased. The CLA production capability ofB. breve, and its tolerance, improved significantly with LA-adaptation. The addition of LA (1 mg/mL) into the culture broth after 24 h of cultivation in a 100-mL media bottle was most effective at promoting CLA production. In a 2.5-L stirred-tank bioreactor, the observed conversion and productivity of 56.6% and 35.4 μgml−1h−1, respectively, by LA-adaptedB. breve were approximately 6.6 and 9.8 times higher than those of LA-unadaptedB. breve.

Fatty acids reduce the tensile strength of fungal hyphae during cephalosporin C production in Acremonium chrysogenum

Fragmentation rate constants, which can be used to estimate the tensile strength of fungal hyphae, were used to elucidate relationships between morphological changes and addition of fatty acids during cephalosporin C production in Acremonium chrysogenum M35. The number of arthrospores increased gradually during fermentation, and, in particular, was higher in the presence of rice oil, oleic acid or linoleic acid than in their absence. Because supplementation of rice oil or fatty acids increased cephalosporin C, we concluded that differentiation to arthrospores is related to cephalosporin C production. To estimate the relative tensile strengths of fungal hyphae, fragmentation rate constants (kfrag) were measured. When rice oil, oleic acid, or linoleic acid were added into medium, fragmentation rate constants were higher than for the control, and hyphal tensile strengths reduced. The relative tensile strength of fungal hyphae, however was not constant presumably due to differences in physiological state.

Efficient Immobilization Technique for Enhancement of Cellobiose Dehydrogenase Activity on Silica Gel

In this study, cellobiose dehydrogenase (CDH) of Phanerochaete chrysosporium ATCC 32629 was immobilized on silica gel for the further application of CDH in the saccharification process of biomass. To prevent the loss of enzyme activity during enzyme immobilization, the pretreatment of CDH was performed by various pretreatment materials before immobilization. When pretreated enzymes were used in immobilization, the activities of immobilized CDH were higher than non-pretreated CDH even in same amounts of immobilized protein. The specific activity of pretreated immobilized CDH with lactose was about two times higher than that of non-pretreated immobilized CDH. Moreover, the pretreated immobilized CDH showed better reusability than non-pretreated immobilized CDH, with 67.3% of its original activity being retained after 9 reuses.