Toshimasa Yano

LIPASE ACTIVITY AND STABILITY IN SUPERCRITICAL CARBON DIOXIDE

Abstract The use of a supercritical fluid as a medium for enzymatic reaction was investigated with respect to its application and reaction mechanism. Lipase could catalyze the reaction of hydrolysis and interes-terification in supercritical carbon dioxide at 35°C and 137 bar. There was no difference in the time course of interesterification between the untreated lipase and the lipase exposed to supercritical carbon dioxide indicating that the enzyme was not severely damaged.

Fundamental Studies on the Aerobic Fermentation

The oxygen uptake rate of aggregated mycelia is decreased to an extent which, in the case of a typical spherical aggregate, could be estimated depending on its diameter, mycelial density, oxygen diffusivity, and so forth. Equations were presented in this paper to evaluate the oxygen uptake rate of an mold pellet. A favorable agreement was found between the calculation and the experiment.

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.

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.

Kinetic Studies on Microbial Activities in Concentrated Solutions.: Part. I. Effect of Excess Sugars on Oxygen Uptake Rate of a Cell Free Respiratory System

Decreases of respiration rates in the presence of excess sugars, substrates and non-substrates, were investigated kinetically on the cell free preparation of a Pseudomonas. The schemes of enzyme inhibition which include successive inactive complexes of one mole of enzyme and two and three moles of substrate or one mole of enzyme and one and two moles of inhibitor were shown to fit the experimental results. Water concentrations were not enough to explain the different inhibitory properties of sugars.

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.

Scaling analysis on elasticity of agarose gel near the sol–gel transition temperature

Abstract The elastic shear modulus G′ of gel and the correlation length ξ were, respectively, described by G′∝ϵ t (1) ξ∝ϵ −ν (2) where ϵ is the deviation from sol–gel transition point (ϵ=|P−Pc| in percolation; P: percolation probability, Pc: percolation threshold), t is the critical exponent of the elastic shear modulus and ν is the critical exponent of the correlation length. We experimentally evaluated not only the elastic modulus of a sol–gel transition system but also the correlation length, since the critical exponent t is related to spatial dimension and the critical exponent of correlation length, depending on the characteristics of elasticity. We could determine the correlation length of agarose gel by the dynamic light scattering method. The temperature dependence of the elasticity of agarose gel was evaluated by the ellipticity as the percolation parameters. The correlation length also diverged when the ellipticity approached the sol–gel transition point. The logarithm of the correlation length was a linear function of the logarithm of the deviation in ellipticity from the sol–gel transition point. The critical exponent of the elastic modulus was described by the scaling law (t=1+ν(d−2); d: spatial dimension), which De Gennes drew on the basis of the scalar elasticity neglecting the bending deformation for a network chain. This suggests that agarose fibers are stiff enough to show the scalar elasticity.

Effective thermal diffusivity of food gels impregnated with air bubbles

A predictive model of the effective thermal diffusivity of food gels impregnated with air bubbles was proposed. The model included the effect of latent heat transport accompanied by water vapor diffusion within the bubbles in addition to heat conduction. To discuss the reliability of the model, the effective thermal diffusivities of several air-impregnated gels were measured and compared with the predicted values. For air-impregnated gels of low water content, the effective thermal diffusivities measured at 20°C were in good agreement with the predicted values. For air-impregnated gels of high water content, the effective thermal diffusivities were well approximated by the predicted values up to 50°C. At higher temperatures, the model tended to overestimate the effective thermal diffusivity especially for the gels of high porosity.

Critical bubble radius for expansion in extrusion cooking

Abstract Strong wheat flour, weak wheat flour and rice flour were expanded by sudden reduction in pressure at the discharge port of an extruder. Their micropore-volume distributions were measured by nitrogen adsorption isotherms. The results were compared with the theoretical critical radius for expansion calculated from the balance of forces acting inside and outside a bubble. The micropore volume near the theoretical critical radius for expansion of an extrudate decreased remarkably after extrusion cooking, indicating that the theoretical critical radius for expansion almost coincided with the experimental one.

Viscoelastic behavior of an agar—gelatin mixture gel as a function of its composition

Abstract The stress relaxation behavior of an agar—gelatin mixture gel was analyzed as a function of the stress relaxation behaviors of the component agar and gelatin gels. A six-element model composed of three components of the Maxwell mechanical model was applicable for each stress relaxation behavior. Except for the behavior of the shortest relaxation time, the three elastic moduli of the mixture gel, including the instantaneous elastic modulus, became predictable from the corresponding moduli of the agar and the gelatin gels, taking into account the concentration dependence and using a parallel-series combination model for the elasticity. The viscosities of the mixture gel were also predictable from the corresponding viscosities of the component agar and gelatin gels, except for the behavior of the shortest relaxation time.