Tomoaki Hagiwara

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.

Fractal analysis of aggregates in heat-induced BSA gels

Abstract The fractal structure of the aggregates in heat-induced bovine serum albumin (BSA) gels was analyzed. Three kinds of BSA gels were prepared by heating BSA solutions: (i) pH 5.1 without CaCl 2 ; (ii) pH 7.0 with 30 mmol/dm 3 CaCl 2 ; and (iii) pH 7.0 with 5 mmol/dm 3 CaCl 2 . First, from the concentration dependences of elasticity for the gels, using the theory of Shih et al. on colloidal gels, the fractal dimensions were evaluated. These BSA gels showed weak-link behavior according to the theory of Shih et al.: the limit of linearity γ 0 increased with increasing BSA concentration. Second, from the images of the aggregates in the gels obtained with confocal laser scanning microscopy, the fractal dimensions of heat-induced BSA gels were evaluated using the box counting method. The fractal dimensions D f for the three gels evaluated from rheological measurement were close to those evaluated from image analysis, the value of D f for the gels being ∼2.6–2.8.

Analysis of Aggregate Structure in Food Protein Gels with the Concept of Fractal

The fractal structure of the aggregates in food protein gels was analyzed. Three kinds of food protein gels were prepared: (1) β-lactoglobulin (β-LG) gel; (2) 11S soybean globulin gel; and (3) caseinate gel. From the concentration dependence of the gel elasticity, the fractal dimensions Df of the aggregates in the gels were evaluated, according to the theory of Shih et al. These gels showed the weak-link behavior described in the theory of Shih et al The values obtained for Df were 2.6-2.7, which were larger than those predicted by the cluster-cluster aggregation model for a dilute system. In addition, for the β-LG gels, the fractal dimension was also evaluated from the analysis of the gel image obtained with a confocal scanning laser microscopy, the value being close to that evaluated from the concentration dependence of the gel elasticity. These results indicate that the elastic behavior of the aggregate gels is a reflection of fractal structure of the aggregates in the gels.

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.

Molecular simulation of bovine beta-lactoglobulin adsorbed onto a positively charged solid surface.

To obtain detailed insight into the mechanism of beta-lactoglobulin (beta-Lg) adsorption to a stainless steel surface at acidic pH, the adsorption of positively charged beta-Lg to a positively charged surface (Au (100) surface with virtual positive charge) was simulated using classical molecular dynamics. The initial orientation and position of beta-Lg on the surface were determined using Monte Carlo simulation using the implicit water system. Molecular dynamics simulation with the explicit water system was conducted for a 5 ns simulation time to monitor beta-Lg adsorption. To investigate surface charge density effects on adsorption of beta-Lg, the positive charge number per Au atom on the (100) surface, C, was varied from 0 to +0.0250|e|. Stable adsorption occurred in MD simulations when C was equal to or less than +0.0200|e|. Among these surface Au charge conditions, no large difference was observed in the vertical separation distance between the surface and the proteins center of mass, and the orientation angle. This fact indicates that the main interactions contributing to the adsorption were van der Waals interactions. The protein domain contacting the surface was near Thr125, agreeing with previous experimental studies. Considering simulation results and those previous experimental studies suggests a detailed adsorption mechanism of beta-Lg at acidic pH: beta-Lg molecule is adsorbed initially with the specific part of 125-135th residues close to the surface by van der Waals interactions. Simultaneously or subsequently, side carboxylic groups of acidic amino acid residues near the surface in 125-135th residues dissociate, leading to firmer adsorption by attractive electrostatic residue-surface interaction.

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.

Effects of Ionic Substances on the Adsorption of Egg White Proteins to a Stainless Steel Surface

The surface fouling of food processing equipment by proteins was studied by investigating the adsorption of egg white proteins to the surface of stainless steel (SS) at pH 7.4 and 30 °C, and particularly the effects of different types of ionic substances. Ovalbumin and ovomucoid, acidic egg white proteins, were less adsorbed in the presence of phosphate (Pi), a multivalent anion, than in the presence of HEPES, an amphoteric ion. On the other hand, lysozyme, a basic egg white protein, was more adsorbed in the presence of Pi than in the presence of HEPES. Citrate as another multivalent anion and taurine as another amphoteric ion affected the respective adsorption of those egg white proteins similarly to Pi and HEPES. The adsorption of an egg white protein to an SS surface therefore depended on the combination of the type of protein and the effective charge of the coexisting ionic substance. This behaviour can be well explained by assuming that a small ionic substance precedes a protein in attaching to an SS surface, resulting in an alteration to the effective surface charge. Pretreating SS with a Pi buffer lowered the amount of ovalbumin adsorbed with the HEPES buffer, demonstrating that Pi can attach to and remain on the SS surface to affect the subsequent protein adsorption.

Monitoring of adsorption behaviors of bovine serum albumin onto a stainless steel surface by the quartz crystal microbalance based on admittance analysis.

The adsorption process of bovine serum albumin (BSA) onto a stainless steel surface was investigated using the quartz crystal microbalance based on admittance analysis. The adhered mass change ∆m increased with time as a result of contacting the BSA solution, and considerably long period (>2 h) was required for the attainment of the asymptotic values of ∆m as well as dissipation factor ∆D. The relation between ΔD and Δm suggested that the layer of adsorbed BSA molecules became stiffer with increasing time at higher BSA concentration. The relation between Δm after 2 h and the final BSA concentration was described well by the Langmuir adsorption isotherm. However, the time course of Δm clearly deviated from the Langmuir adsorption model. The stretched exponential function model described the time course of Δm well although it was an empirical one.

Recrystallization of Ice Crystals in Trehalose Solution at Isothermal Condition

An isothermal ice recrystallization behavior in trehalose solution was investigated. The isothermal recrystallization rate constants of ice crystals in trehalose solution were obtained at −5 °C, −7 °C, and −10 °C. Then the results were compared to those of a sucrose solution used as a control sample. Simultaneous estimation of water mobility in the freeze-concentrated matrix was conducted by 1H spin–spin relaxation time T2 to investigate mechanisms causing the different ice crystal recrystallization behaviors of sucrose and trehalose. At lower temperatures, lower recrystallization rates were obtained for both trehalose and sucrose solutions. The ice crystallization rate constants in trahalose solution tended to be smaller than those in sucrose solution at the same temperature. Although different ice contents (less than 3.6%) were observed between trehalose and sucrose solutions at the same temperature, the recrystallization behaviors of ice crystals were not markedly different. The 1H spin–spin relaxation time T2 of water components in a freeze-concentrated matrix for trehalose solution was shorter than in a sucrose solution at the same temperature. Results show that the water mobility of trehalose solutions in freeze-concentrated matrix was less than that of sucrose solutions, which was suggested as the reason for retarded ice crystal growth in a trehalose solution. Results of this study suggest that the replacement of sucrose with trehalose will not negatively affect deterioration caused by ice crystal recrystallization in frozen foods and cryobiological materials.