Rikuo Takai

Comparative Investigation by Two Analytical Approaches of Enthalpy Relaxation for Glassy Glucose, Sucrose, Maltose, and Trehalose

No HeadingPurpose.In an effort to understand the stability of glassy sugars such as glucose, sucrose, maltose, and trehalose, the molecular mobility below the glass transition temperature (Tg) was investigated by an enthalpy relaxation measurement with differential scanning calorimetry (DSC).Methods.The glassy sample was aged over several days at (Tg − 10) K to (Tg − 30) K, before a DSC heating scan was taken. The relaxed enthalpy (ΔHrelax) was estimated from the endothermic peak area. The enthalpy relaxation time was analyzed from the time course of ΔHrelax using two different approaches; Kohlrausch-Williams-Watts (KWW) and extended Adam-Gibbs (exAG).Results.τKWW, which is defined as the mean average enthalpy relaxation time in a distribution, and τeff0 and τeff∞, which correspond to the enthalpy relaxation time of the initial minimum and final maximum cooperative rearrangement region, were estimated by KWW and exAG, respectively. And three activation energies for enthalpy relaxation were calculated from the Arrhenius plot.Conclusions.Although these ΔEs originated from different theoretical backgrounds, almost the same trend was observed for a comparison of the values of the four sugars. The finding that the ΔEs of glassy trehalose were the largest among the four sugars may support the reason that glassy trehalose is an effective stabilizer.

Factors affecting the uptake of DMSO by the eggs and embryos of medaka, Oryzias latipes.

High performance liquid chromatography (HPLC) was used to assess the uptake dynamics of the cryoprotectant DMSO by intact unfertilized eggs (stage 0), 8-cell (stage 5) and eyed embryos (stage 30) of medaka, Oryzias latipes, the relation of the internal concentration (Cin) of DMSO with fertilization and survival rates, and the effects of several factors on these processes. The factors examined were: cryoprotectant concentration (0.6, 1.2, 1.9 and 2.5 M), impregnation time (1, 3, 5, 10, 15 and 20 min), temperature (0, 5 and 20 degrees C), hydrostatic pressure (0 and 50 atm), and the osmotic conditions of the materials (normal or partially dehydrated). Cryoprotectant permeation, estimated from the initial rates of DMSO uptake, was higher in embryos than in eggs and increased with embryonic development; however, the DMSO Cin in eyed embryos reached a plateau at 1-5 min and could not be increased by prolonging impregnation. The highest fertilization and survival rates for any given DMSO Cin were obtained with high concentrations and short times of impregnation rather than low concentrations and long impregnation times. Application of hydrostatic pressure (50 atm) and exposure for 3 min to a 1 M trehalose solution prior to impregnation induced a substantial increase in the DMSO Cin of 8-cell embryos in comparison to untreated controls with no significant effect on survival. Hydrostatic pressure also promoted DMSO uptake in unfertilized eggs, but with rapid loss of viability, and was ineffective in eyed embryos. The uptake of DMSO and its toxicity to 8-cell embryos were directly proportional to the temperature of impregnation. The results of this study reveal important interactions between cryoprotectant concentration, impregnation time and the developmental stage (or type) of the materials and provide evidence that hydrostatic pressure, temperature of impregnation and the osmotic conditions of the materials can be manipulated to increase the uptake of cryoprotectant by fish eggs and embryos.

Kinetic process of enthalpy relaxation of glassy starch and effect of physical aging upon its water vapor permeability property

Abstract The enthalpy relaxation during aging below Tg of an amorphous starch was examined via the Kohlrausch–Williams–Watts (KWW) relation in order to describe its kinetic process quantitatively. The experimental data were fitted satisfactorily by the KWW equation of stretched exponential form. Comparison to the results reported in previous studies reveals that both the values of the mean relaxation time τ and the relaxation time distribution β(0.23–0.34) obtained through the fitting process were reasonable. Furthermore, the effect of physical aging below Tg on the water vapor permeability (WVP) of starch film was investigated. The WVP was reduced by aging below Tg, which agreed with the results reported previously for several synthetic polymer systems. Consequently, in the present study, the reduction of moisture transfer during aging can also be interpreted as a result of decreasing free volume, which occurs simultaneously with enthalpy relaxation.

Enthalpy relaxation and glass to rubber transition of amorphous potato starch formed by ball-milling

Ball-milling is known to convert native potato starch into an amorphous state. Using differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD), we demonstrated that the ball-milled amorphous starch exhibits a glass to rubber transition accompanied by a recovery from enthalpy relaxation. Such transition behavior differs from that of the glassy starch formed by heating and subsequent quenching. We further found that the ball-milling process for potato starch enhances the enthalpy and volume relaxation with breaking the crystalline inner native potato starch. In addition, our results suggest that WAXD examination may capture the volume relaxation phenomena of amorphous materials such as starch.

Development of a trimethylamine gas biosensor system

Abstract A trimethylamine (TMA) gas biosensor was developed, based on the immobilized mould, Penicillium decumbens , an oxygen electrode, a flow cell, a peristaltic pump, a recorder and a buffer tank. The optimum conditions for the sensor were: pH 7·6, temperature 30°C, flow rate 0·3 ml/min, and sample volume 50 μl. Upon measurement of TMA concentrations in fish muscle, a good correlation was found between results obtained from the sensor and those obtained from gas-liquid chromatography (GLC). The correlation coefficient was 0·84. Each assay lasted 30 min. The proposed sensor was stable even after 37 days.

Suitability of cryoprotectants and impregnation protocols for embryos of Japanese whiting Sillago japonica.

The purpose of this study was to examine the suitability of cryoprotectant agent (CPA) impregnation protocols for the embryos of Japanese whiting (Sillago japonica), a small-sized, easy-to-rear, and prolific marine fish which may constitute a suitable experimental material for the development of cryopreservation methods for fish embryos. Our immediate goals were to assess the toxicity and permeability of various CPAs to whiting embryos of different developmental stages. Exposure of gastrula, somites, tail elongation, and pre-hatching embryos to 10%, 15%, and 20% solutions of propylene glycol (PG), methanol (MeOH), dimethyl sulfoxide (Me2SO), dimethylformamide (DFA), ethylene glycol (EG), and glycerol (Gly) in artificial sea water (ASW; 33 psu) for 20 min revealed that CPA toxicity for whiting embryos increased in the order of PG<Me2SO<DFA<EG<MeOH<Gly. Relative CPA permeability, estimated by proton nuclear magnetic resonance spectroscopy, showed the same trend as toxicity except for Gly, which was highly toxic but showed only moderate permeability. There were no marked differences in CPA tolerance between developmental stages except for a slight decrease in pre-hatching embryos. Stepwise (20% x 5 steps) impregnation with CPA mixtures of 20-25% PG with 10-15% DFA, Me2SO, MeOH, or EG in ASW were well tolerated by the embryos. Overall, the results of toxicity and permeability suggest that PG, MeOH, and EG could be useful for the development of CPA solutions for whiting embryos.

Maillard Reaction Rate in Various Glassy Matrices

The Maillard Reaction (MR) rate below the glass transition temperature (Tg) for various model glassy food systems was studied at temperatures between 40 °C and 70 °C. As a sample, freeze-dried glucose and lysine systems embedded in various glassy matrices (e.g., polyvinylpyrrolodone and trehalose) were used, and the MR rate below the Tg was compared among the various glassy matrices. The extent of MR was estimated spectrophotometrically from the optical density at 280 nm (OD280), and the MR rate (k280) was determined as a pseudo zero order reaction rate from the time course of OD280. Although k280 was described by the Arrhenius plot, the temperature dependence of k280 was almost the same and the intercept was different among the matrices. From the comparison of k280, it was suggested that the MR rate in glassy matrix was affected not only by the Tg, but also by the hydrogen bonding between MR reactants and glassy matrix.

Determination of dehydroascorbic acid by an enzyme sensor system with a parallel flow cell

Abstract An enzyme sensor system was developed for the determination of dehydroascorbic acid and L-ascorbic acid. The system was constructed from a parallel flow cell separated by a dialysis membrane, an immobilized ascorbate oxidase membrane, coupled to a Clark-type oxygen electrode, and L-cysteine, which was present as a reductant. The method is based on the reduction of dehydroascorbic acid to L-ascorbic acid with L-cysteine in a parallel flow cell. One assay for dehydroascrobic acid could be completed within 8 min. Linear calibration curves for dehydroascorbic acid and L-ascorbic acid were observed in the range of 20 mM–100 mM and 2 mM–20 mM, respectively.

Analysis of heat-induced BSA aggregates by scattering methods

Publisher Summary Scattering methods are very effective to analyze colloidal structure below hundred nanometers. The analysis of aggregate structure on such scale using the scattering methods would help us to guess the mechanism of development of the fractal structure in protein aggregate gels. Light scattering provides information on dilute colloidal structure on the scale length from decades to hundreds nanometers. The investigation on the dilute system is very important because dilute colloidal system has been theoretically examined on the basis of the cluster-cluster aggregation model. This chapter presents a study in which the structure of aggregates formed by heating dilute bovine serum albumin (BSA) solution is analyzed using a laser light scattering method. The fractal structure is observed on the scale length from decades to hundreds nanometers. With increase in salt concentration of the solution, the value of fractal dimension Df for the aggregates tends to increase, suggesting that the aggregates are reconstructed by salt addition. The aggregate structure in BSA gels prepared from concentrated solution is also investigated using a small angle X-ray scattering method on the scale length from several to decades nanometers. It is suggested that the aggregates in the gels are formed through the process different from the conventional cluster–cluster aggregation model.