Hiroyuki Sasahara

Purification and characterization of two xylanases and an arabinofuranosidase from Aspergillus sojae

Abstract Two isoenzymes of xylanase (endo-1,4-β-xylanase, EC 3.2.1.8) and an arabinofuranosidase (α- l -arabino-furanosidase, EC 3.2.1.55) were purified as electrophoretically homogeneous proteins from a solid-state culture of Aspergillus sojae . The molecular weights of the xylanases (X-I and X-II-B) and arabinofuranosidase (X-II-A) were estimated to be 32,700, 35,500 and 34,300, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Gel filtration chromatography gave molecular weight values similar to those obtained by SDS-PAGE for each of the purified enzymes. The isoelectric points of X-I and X-II-B were 3.50 and 3.75, and that of X-II-A was 3.90. The maximum velocities of arabinoxylan degradation by the xylanases were attained at 60°C (X-I) and 50°C (X-II-B), when the pH was maintained at 5.5. The xylanases were stable from pH 5.0 to 8.0, and up to 50°C (X-I) and 35°C (X-II-B). The optimum pH and temperature of X-II-A were 5.0 and 50°C, respectively, and it was stable from pH 5.0 to 9.0 and up to 50°C. The activity of these three enzymes was significantly inhibited by Mn 2+ and EDTA, and stimulation by metal ions was not observed. Amino acid composition and sequence of the amino-terminus indicated that the xylanases of A. sojae were distinct from other known Aspergillus xylanases.

Production of D-Talitol from D-Psicose by Candida famata R28

A halotolerant yeast strain R28 that can convert d-psicose to d-talitol was isolated from soy sauce mash and identified as Candida famata. The cells grown on l-sorbose were found to have the best conversion potential. C. famata R28 converted d-psicose to d-talitol at a faster rate in the presence of various carbohydrates such as erythritol, d-sorbitol, ribitol and glycerol in the reaction mixture. At 10% substrate concentration, the conversion ratio was above 90% using washed cells when 5% d-sorbitol was added to the reaction mixture. Moreover, for production of d-talitol by a fermentation reaction with C. famata R28, the conversion ratio was about 80% at 10% substrate concentration, and more than 98% of the substrate consumed was converted to d-talitol.

Rapid continuous lactic acid fermentation by immobilised lactic acid bacteria for soy sauce production

Abstract Continuous lactic acid fermentation was carried out to produce an appropriate feed solution for rapid ethanol fermentation in soy sauce production. Lactic acid bacteria were immobilised physically within porous alumina ceramic beads and the fermentation substrate was a filtered extract of soy sauce mash. Lactic acid concentration was controlled by dilution rate. The volumetric production rate was dependent on the dilution rate and was much higher than that in batch fermentation. The lactic acid productivity was mathematically modelled from the basic material balance and the rate equation. The simulated results agreed with the experimental ones.

Porous alumina beads for immobilization of lactic acid bacteria and its application for repeated-batch fermentation in soy sauce production

Abstract Porous alumina beads with controlled pores were prepared for the immobilization of lactic acid bacteria to improve soy sauce productivity, and the alumina support with the highest lactic acid productivity was used for repeated-batch fermentation. Immobilized lactic acid bacteria could be used 5 times in repeated-batch fermentation, where higher productivities were obtained than that in conventional fermentation. The lactic acid fermentation process was mathematically modeled from the material balance and the rate equation. The simulated results agreed with the experimental ones.

Rapid ethanol fermentation for soy sauce production using a microfiltration membrane reactor

Abstract Continuous ethanol fermentation of a filtrate solution from a soy sauce mash was conducted to improve soy sauce productivity by the simultaneous use of a stirred tank reactor and a microfiltration membrane. Soy sauce yeast cells were maintained within the reactor system with a rejection rate over 0.99 by the membrane. The concentrations of ethanol and glucose in the retentates and the permeates were mathematically modeled from the material balance and the rate equations, and the simulated results agreed well with the experimental ones. Ethanol concentration was dependent of the dilution rate, and its highest value was obtained at a transmembrane pressure of 1 kPa. The volumetric ethanol productivity obtained was several times higher than those in batch and immobilized cell systems.

Rapid Ethanol Fermentation for Soy Sauce Production by Immobilized Yeast Cells

Continuous ethanol fermentation was done to improve soy sauce productivity using immobilized soy sauce yeast cells. The yeast cells were immobilized physically in pores of alumina ceramic beads, and fermentation was done with a filtrate solution from soy sauce mash. The ethanol concentration was controlled by the dilution rate, and the volumetric production rate, being dependent on dilution rate, was found to be much higher than that in batch fermentation. The ethanol production system was mathematically modeled from the basic material balance and the rate equation. The simulated results agreed with the experimental ones. The reactor system with immobilized yeast cells was effective for obtaining ethanol with a high production rate.

Succinate Metabolism of Isolated Soybean Nodule Bacteroids at Low Oxygen Concentration

The effects of various concentrations of succinate in the incubation system on ARA and oxidative succinate degradation by nodule bacteroids were analyzed. When the bacteroids’ ARA was measured in various concentrations of succinate the highest ARA was observed at 2mM succinate, and the activity was lower at higher succinate concentrations.To monitor the oxidative degradation of exogenous 2,3-14C-succinate by nodule bacteroids the formation of 14CO2 was measured continuously with or without Lb.In 1% oxygen 14CO2 was formed actively by bacteroids at 0.5 to 3mM succinate, but at 4 or 8mM succinate the bacteroid’s 14CO2 formation was almost negligible. The bacteroids did not release 14CO2 with no oxygen in the incubation system.Addition of Lb (100mM) to the incubation system stimulated the 14CO2 formation at all concentrations of succinate in 1% O2, especially at 4 or 8mM succinate the succinate oxidation was greatly improved.The pathway of succinate degradation in the bacteroids was analyzed when the incubat...

Production of D-iditol from D-sorbose by Rhodotolura rubra RY10 isolated from Miso paste

The yeast strain RY10 that can convert D-sorbose to D-iditol was isolated from miso paste and identified as Rhodotolura rubra. The cells grown on D-fructose were found to have relatively high conversion potential. Addition of ethanol to the reaction mixture significantly accelerated the conversion rate of D-sorbose to D-iditol. During the conversion reaction, ethanol was added to the reaction mixture at 48 h intervals to maintain the concentration of ethanol at 1.0%. The final conversion ratios were 82.7%, 95.0%, 93.7%, and 78.0% using washed cells when the concentration D-sorbose were 1.0%, 2.0%, 3.0% and 5.0%, respectively. The product produced from D-sorbose was identified as D-iditol by high performance liquid chromatography analysis, infrared spectrum, optical rotation and melting point measurements.