Moon H. Han

Continuous ethanol production by immobilized yeast in a fluidized reactor

SummaryIn order to minimize the adverse effect of CO2 gas in a packed bed immobilized yeast reactor, a fluidized bed reactor was used for the continuous production of ethanol from glucose. Immobilized yeast was prepared by entrapping whole cells of Saccharomyces cerevisiae within a Caalginate matrix. It was found that the efficiency of the ethanol production in a fluidized bed reactor was 100% better than that for a packed bed reactor system. The alcohol productivity obtained was 21 g/l/hr in a fluidized bed reactor at 94% of conversion level.

Ethanol production from cassava and sago starch using Zymomonas mobilis

SummaryCassava and sago starch were evaluated for their feasibilities as substrates for ethanol production using Zymomonas mobilis ZM4 strain. Before fermentation, the starch materials were pretreated employing two commercial enzymes, Termamyl (thermostable α-amylase) and AMG (amyloglucosidase). Using 2 μl/g of Termamyl and 4 μl/g of AMG, effective conversion of both cassava and sago starch into glucose was found with substrate concentration up to 30%(w/v) dry substances. Fermentation study performed using these starch hydrolysates as substrates resulted in ethanol yield at an average of 0.48g/g by Z. Mobilis ZM4.

Rifamycin B. oxidase from Monocillium spp., a new type of diphenol oxidase

It was found that enzyme from a microbial strain, Monocillium spp. ATCC 20621, catalyzed the oxidative reaction of rifamycin B to form rifamycin O. The identification of the reaction products suggested that the reaction proceeded by the oxidative cyclization of rifamycin B to give rifamycin O, which spontaneously hydrolyzed to rifamycin S in neutral aqueous milieu. The characteristic of the enzyme was different as compared with that of other polyphenol oxidases such as laccase. It is proposed that this new type of enzyme be classified into a subgroup EC 1.10.3.6 with a trival name rifamycin B oxidase.

Simultaneous saccharification and ethanol fermentation of sago starch using immobilized Zymomonas mobilis

Abstract Simultaneous saccharification and ethanol fermentation (SSF) of sago starch using amyloglucosidase (AMG) and immobilized Zymomonas mobilis ZM4 on sodium alginate was studied. The immobilized Zymomonas cells were more thermo-stable than free Zymomonas cells in this system. The optimum temperature in the SSF system was 40°C, and 0.5% (v/w) AMG concentration was adopted for the economical operation of the system. The final ethanol concentration obtained was 68.3 g/ l and the ethanol yield, Y p/s , was 0.49 g/g (96% of the theoretical yield). After 6 cycles of reuse at 40°C with 15% sago starch hydrolysate, the immobilized Z. mobilis retained about 50% of its ethanol fermenting ability.

Continuous ethanol production from sago starch using immobilized amyloglucosidase and Zymomonas mobilis

Abstract To produce ethanol more economically than in a conventional process, it is necessary to attain high productivity and low production cost. To this end, a continuous ethanol production from sago starch using immobilized amylogucosidase (AMG) and Zymomonas mobilis cells was studied. Chitin was used for immobilization of AMG and Z. mobilis cells were immobilized in the form of sodium alginate beads. Ethanol was produced continuously in an simultaneous saccharification and ethanol fermentation (SSF) mode in a pacekd bed reactor. The maximum ethanol productivity based on the void volume, V v , was 37 g/ l /h with ethanol yield, Y p/s , 0.43 g/g (84% of the theoretical ethanol yield) in this system. The steady-state concentration of ethanol (46 g/ l could be maintained in a stable manner over two weeks at the dilution rate of 0.46 h − .

Immobilization of Zymomonas mobilis and amyloglucosidase for ethanol production from sago starch

Abstract Immobilization of amyloglucosidase ( AMG ) and Zymomonas mobilis cells was studied in order to produce ethanol from sago starch economically. Among various immobilization methods tested, a coimmobilized system using chitin and sodium alginate appeared most promising with respect to ethanol productivity and operational stability. When the system was run in the continuous simultaneous saccharification and fermentation ( SSF ) mode, the maximum ethanol productivity was found to be 72.2 g l −1 h −1 at a dilution rate of 3.28 h −1 . This system could be run in the stable manner over 40 days with a steady-state ethanol concentration of 44 g l −1 and an ethanol conversion yield of 93% .

The properties of immobilized whole cell ofHumicola spp. with rifamycin oxidase activity

SummaryThe whole cell ofHumicola spp. ATCC 20620 with rifamycin oxidase activity was immobilized by copolymerization with acrylamide. The whole cell was defatted by treatment with acetone to reduce the diffusional resistance through the cell membrane. The recovery of enzyme activity after the immobilization step was about 50%. The acetone-defatted cell showed the maximum activity at pH 7.5 for both free and the immobilized forms. No appreciable activity loss could be detected when stored at 4 °C and pH 7.8 for one month, while the half life at 40 °C and pH 8 was decreased to about 8 days. The apparent Km values of rifamycin oxidase for the free and immobilized acetonedefatted cells were 0.3mM and 0.6mM, respectively. The enzyme demonstrated substrate inhibition, but the degree of substrate inhibition was different between two forms of the enzyme preparation. A complete substrate inhibition was observed for the immobilized cell, whereas the enzyme activity was partially inhibited at high substrate concentration in the acetone-defatted cells.

Studies on microbial glucose isomerase: 4. Characteristics of immobilized whole-cell glucose isomerase from Streptomyces spp.

Whole-cell glucose isomerase from a Streptomyces spp. was immobilized by entrapment in gelatin matrices crosslinked with glutaraldehyde. The resultant immobilized enzyme preparation had up to 40% recovery yield of the activity and showed relatively long stabilities during storage and the isomerizing reaction. The storage half-life of the preparation was 19 months at 5°C and the half-life of the enzyme during operation was 260 days in the presence of 1 mM Co2+ and 80 days in the absence of the metal ion. Optimum pH and temperature were 7.5 and 70–75°C, respectively. The Km values for glucose and fructose were 0.29 and 0.46 m, respectively, with a maximum theoretical conversion yield of 56%. The simulation results based on the reversible one-substrate enzyme kinetic model agreed well with the experimental data obtained from a batch reactor. The continuous operation of packed bed reactors demonstrated that some effects of the external film diffusion resistance were apparent at low flow rates of the substrate feed solution, whereas the internal pore diffusion resistance was negligible up to the pellet size used in this work.

A GRAPHICAL METHOD OF DETERMINING THE MICHAELIS-MENTEN CONSTANT FREE OF EXTERNAL MASS TRANSFER RESISTANCE FOR IMMOBILIZED ENZYMES IN A PACKED BED REACTOR

SummaryA graphical method of determining the Michaelis-Menten constant free of the external mass transfer resistance for a packed bed immobilized enzyme system was illustrated with examples from 3 different enzyme reactions. The intercept at the ordinate obtained by the straight line extrapolation of data points in the plot of apparent Km value vs. the reciprocal of superficial velocity in column allowed an easy calculation of Km free of external mass transfer resistance. An asymptotic value of apparent Km value at infinite zero superficial velocity was ascribed to the fact that the mass transfer coefficient kL, approached a definite value at this condition.

Plasmid maintenance and growth of recombinantSaccharomycescerevisiae producing hepatitis B virus surface antigen

SummaryThe effects of host strains (Saccharomycescerevisiae) and medium composition on the plasmid stability and expression level of hepatitis B virus surface antigen were investigated. Specific growth rates of cells carrying a plasmid, pMHBS, was found to be slower than those without the plasmid. It was also found that the plasmid was maintained in a more stable manner in the selective medium. The nonselective complex medium, however, was greatly favored for the growth of recombinant hosts as well as the HBsAg production.