Osato Miyawaki

Determination of log P for pressurized carbon dioxide and its characterization as a medium for enzyme reaction

The log P value of pressurized CO(2) at 50 degrees C was determined from the solubility of 1-octanol in CO(2) and compared with other solvent parameters such as permittivity, epsilon, and polarity parameter, E(T)(30). The log P indicated that pressurized CO(2) is rather hydrophilic although it seems hydrophobic being judged from epsilon(r) and E(T)(30). With a change in pressure from 3 to 11.8 MPa, the log P changed from 0.9 to 2.0 while epsilon(r) and E(T)(30) changed only slightly. The log P was linearly correlated to the logarithm of the solubility of water among organic solvents. Pressurized CO(2) was located close to the linear correlation line among the solvents at high pressure (>11 MPa) but its location deviated to the hydrophilic side with a decrease in pressure. Lipase-catalyzed esterification of stearic acid with ethanol and hydrolysis of ethyl stearate were carried out in pressurized CO(2), benzene (log P = 2.0), and n-hexane (log P = 3.5). In spite of the lowest log P value for CO(2), the reaction rate in CO(2) was the highest among solvents tested in pressure range over 10 MPa. The reaction rate was strongly dependent on pressure of CO(2).

Effect of seed ice on formation of tube ice with high purity for a freeze wastewater treatment system with a bubble-flow circulator

A freeze wastewater treatment system with a bubble-flow circulator is advantageous from an industrial point of view because a bubble-flow circulation requires much less energy for the mixing of the wastewater to facilitate heat, mass and momentum transfers in the system than that using agitators or pumping circulation. In this work an ice tube was produced in a bubble-flow circulator and the effect of seed ice crystals on tube ice formation with a high purity was investigated. Without seed ice crystals a large supercooling appears before ice crystal formation and dendritic ice crystals are suddenly formed. Components in wastewater are contaminated and trapped between dendritic ice crystals, resulting in poor quality in the wastewater treatment. To avoid abrupt ice crystallization it is necessary to keep supercooling small. A seed ice crystal is effective for this purpose because a seed ice crystal generates other ice crystals, resulting in no supercooling. Model wastewater including polypeptone with concentrations of 5000 and 10000 ppm, corresponding to 1290 to 3800 ppm in COD (chemical oxygen demand) was used. Two kinds of experiments with different types of seed ice addition were examined. In each concentration examined more than 30% COD normalized by initial COD was confirmed in the melted ice tube with no seed ice. On the other hand, only a few % of COD of the initial values were detected when seed ice crystals were used to initiate the ice tube formation.

Freezing and Ice Structure Formed in Protein Gels

Ice structure was photographically analyzed for frozen soy protein curd and egg albumin gel frozen under various conditions. Dendritic ice structure was observed growing from the cooling plate parallel to the direction of the heat flux. The change in the ice structure size was analyzed at different locations from the cooling plate in the plane perpendicular to the direction of heat flux. In accordance with the theoretical relationship proposed by us before, the mean ice structure size was inversely proportional to the moving speed of the freezing front and the proportionality constant was not very much different from the diffusion coefficient of water, showing the important role of the molcular diffusion mechanism in the process of ice crystal growth. For the freezing accompanied with supercooling, the ice structure became very small, reflecting the very rapid moving speed of the freezing front when supercooling ceased. The theoretical model by us had advantages over the models proposed in the literature for its simple theoretical basis and wider applicability.

Transesterification between triolein and ethylbehenate by immobilized lipase in supercritical carbon dioxide

Abstract Transesterification between triolein (OOO) and ethylbehenate (EB) was carried out to produce 1,3-dibehenoyl-2-oleoyl glycerol. (BOB), an antiblooming agent for chocolate, by 1,3-regiospecific immobilized lipase (Lipozyme IM) in supercritical carbon dioxide (SCCO 2 ). An increase in the concentration of EB accelerated the transesterification activity to BOB while an increase in the concentration of OOO was inhibitory, suggesting that the transesterification proceeds via behenoyl-enzyme complex. The optimum water content in immobilized enzyme for transesterification increased with an increase in the initial substrate concentration. The optimum temperature and pressure for the maximum productivity of BOB were determined to be 50°C and 15 MPa, respectively, as determined from both the initial period activity and the reaction equilibrium.

Conditions of producing an ice layer with high purity for freeze wastewater treatment

Abstract A freeze wastewater treatment has several advantages: (1) wastewater, including toxic compounds which is difficult to be treated biologically can be treated; (2) the ice crystals produced can be used for cold heat storage; and (3) a smaller facility is required than that for biological wastewater treatment. However, freeze wastewater treatment does not currently prevail in the world. This is because low-purity ice crystals are produced, resulting in poor wastewater treatment. In this paper, conditions of producing an ice layer with high purity were investigated. An ice layer was formed on an aluminum plate heat exchanger. Model wastewater including polypepton with concentrations from 2000 ppm, to 10000 ppm corresponding to 670 ppm to 3800 ppm in chemical oxygen demand (COD) was used. A seed ice layer was effective for producing an ice layer of higher purity. The greater the flow rate on the plate heat exchanger, the higher the purity of the ice layer involved, resulting in 10–30 ppm in COD at the superficial flow rate of 0.3 m/s regardless of the initial COD levels. The coolant temperature also affected little to produce an ice layer with high purity, whether the coolant temperature was 268 K or 263 K.

Relationship between the electrical and rheological properties of potato tuber tissue after various forms of processing

The impedance at frequencies of 1-1000 kHz and dynamic bending storage modulus measured by the vibrating reed method were compared for potato tuber tissue, which had been processed by various methods. Raw potato tuber tissue strips were either heated for 30 min up to 100°C or frozen-thawed. Some samples were osmotically dehydrated in a mannitol solution up to a concentration of 0.7 mol/l. The electrical reactance correlated well with the storage modulus of heated or frozen-thawed potato tissues, but not with the storage modulus of the mannitol-treated tissue. The storage modulus appeared to be strongly dependent on the turgor pressure of the cells which was drastically decreased by the heating, freezing-thawing, and osmotic treatments. The electrical properties reflect the cell integrity, and a large difference was observed between the change in impedance after heating or freezing-thawing, and that after the osmotic treatment. A significant change in the electric properties was also observed for a starch suspension at the gelatinization temperature. However, the contribution due to gelatinization did not appear to play an important role in the change of electrical properties of potato tissue by heating.

The sol–gel preparation and characterization of nanoporous silica membrane with controlled pore size

Abstract A thin nanoporous silica membrane was prepared by the two-step sol–gel method. First, silica membrane was formed onto the α-alumina support as an intermediate layer with fibrous silica colloid. Then, silica nanoparticles were deposited on the first layer of silica membrane surface again by the sol–gel method. It is generally found that gelation process, as liquid evaporates during drying, begins with the formation of fractal aggregates. Since an aggregate having the higher fractal dimension has the more complex void space than the aggregate having the lower fractal dimension, the silica nanoparticle concentration in the coating solution for the second step modification was selected low enough to avoid the aggregates with the higher fractal dimension. Thus, the prepared membrane had a dense skin layer with a nanospace as interparticle void space, which was proved by the AFM surface image analysis and the result from nitrogen adsorption porosimetry.

Dielectric Relaxation of Aqueous Solution with Low-molecular-weight Nonelectrolytes and Its Relationship with Solution Structure

Dielectric relaxation of water molecules was measured in the frequency range from 0.2 to 20 GHz for aqueous solutions of urea, formamide, alcohols, and saccharides. The relaxation behavior was described well by the Debye equation with a single relaxation process in most cases. The static permittivity of solution and relaxation time of water in solution changed linearly with solute concentration. The relaxation time shift of water molecules through the existence of solute was correlated well to the first virial coefficient of the activity coefficient of water suggesting the close relationship between dielectric relaxation time and aqueous solution structure.

Effects of water activity and aqueous solvent ordering on thermal stability of lysozyme, α-chymotrypsinogen A, and alcohol dehydrogenase

Effects of water activity (aW) and solvent ordering were separately analyzed on the thermal unfolding of lysozyme and alpha-chymotrypsinogen A, and also on the thermal deactivation of yeast alcohol dehydrogenase (YADH) in aqueous solutions with various additives. With the coexistence of additives, water activity was the determinant of the extent of the change in the thermal stability of proteins while solvent ordering was the determinant of the direction of the change. The parameter alpha, determined from the activity coefficient of water, representing the deviation of aW from that of the ideal solution, was useful as a quantitative index of the solvent ordering showing good correlations with the unfolding temperature and enthalpy of lysozyme and alpha-chymotrypsinogen A and also with the thermal deactivation rate constant of YADH at a constant aW. Solvent ordering seemed to affect the thermal stability of proteins mainly through its effect on the intramolecular hydrophobic interaction among amino acid residues in a protein molecule but the contribution of the electrostatic interaction including hydrogen bonding through the change in permittivity of solution was also suggested.

Electrochemical bioreactor with immobilized glucose-6-phosphate dehydrogenase on the rotating graphite disc electrode modified with phenazine methosulfate

Physical adsorption, covalent binding through the carbodiimide reaction between the surface carboxyl group and the amino group of the protein, and the crosslinking method with bovine serum albumin by glutaraldehyde were applied for the immobilization of glucose-6-phosphate dehydrogenase (G6PDH) on a graphite electrode. Among those, the crosslinking method was employed for its highest apparent enzyme activity per unit surface area. Phenazine methosulfate (PMS), as a mediator for the electrochemical oxidation of NADH, was also immobilized on the graphite surface through adsorption. The conjugation reaction of G6PDH and the electrochemical oxidation of NADH were confirmed by cyclic voltammetry and the constant potential electrochemical reaction. An electrochemical bioreactor system was established by using a rotating disc graphite electrode with G6PDH immobilized. The coenzyme, NAD, was effectively recycled between the electrochemical and the enzymatic reactions.