Dielectric spectroscopy has been widely used to study molecular dynamics in dispersed systems. With an increase in frequency, the dielectric constant, ε', often decreases, the electric conductivity σ' increases, and the dielectric loss, ε”, shows a peak, due to the delay in dipole moments, this phenomenon being the so-called dielectric relaxation. By fitting dielectric relaxation data to semiempirical equations, for example, the Cole-Cole equation, one can obtain a parameter reflecting the mobility of molecules, polymer chains and so forth, such as the relaxation time, τ, which corresponds to the time needed for electric dipoles to orient in the direction of an electric field. The application of the dielectric relaxation to food hydrocolloids such as BSA solution, gelatin solution, alginate solution, and so forth was reviewed. Each dielectric relaxation observed is considered to be ascribable to a different fluctuation or movement of “components” in the electric field among different hydrocolloid systems, thus giving information on the inner structure of the hydrocolloids.
The disappearance and discoloration of L-ascorbic acid 2-glucoside powders with water contents of 2 to 12% (w/w) during storage at a temperature from 70 to 90°C were investigated. The disappearance of L-ascorbic acid 2-glucoside with the higher water content proceeded faster at the higher temperature. The disappearance process was expressed by the Weibull equation. The change in the L-ascorbic acid was analyzed by assuming that both the hydrolysis and decomposition of L-ascorbic acid were expressed by first-order kinetics. A kinetic comparison of the overall disappearance by the hydrolysis indicated that the hydrolysis was not the sole route for the disappearance. The discoloration kinetics was also analyzed on the basis of the modified Weibull equation. It was shown that the enthalpy-entropy compensation held for all the processes involved in the overall disappearance of L-ascorbic acid 2-glucoside, its hydrolysis, the decomposition of L-ascorbic acid and the discoloration of L-ascorbic acid 2-glucoside. It was also demonstrated that the discoloration was suppressed by the glucosylation of L-ascorbic acid, but that L-ascorbic acid 2-glucoside was more easily discolored than L-ascorbyl 6-palmitate.
The partial decomposition reaction of starch in hot-compressed water was studied using a tubular reactor at 160-210°C and 25-45 MPa. The increase rate of reducing sugar concentrations at short residence times was considered as initial reaction rate of partial decomposition. The kinetic analysis of the initial reaction rate indicated that the reaction mechanism over 190°C was different from that below 180°C . The reaction mechanism over 190°C could be expressed by bimolecular reaction between starch and ionized water. The activation energies for starch partial decomposition were about 120 kJ/mol, which was almost the same as the activation energies of maltose and isomaltose hydrolysis. The activation volumes were equivalent to the volume of a few water molecules, suggesting that the reaction proceeded like the gas phase reactions. In contrast, the reaction mechanism below 180°C could be expressed by multimolecular reaction. The activation volumes were significantly larger than those over 190°C . The large activation volume below 180°C suggested that the reaction proceeded, like the liquid phase reactions, with solvent effect between starch and multiple water molecules.
Changes in mechanical properties of a sample soybean seed during experimental Natto making process were studied from a histological standpoint. The process for Natto making was partitioned into soaking, autoclaving, fermenting and aging operations by which physical structures of a soybean seed were influenced. The hardness of the sample soybean was drastically changed by the autoclaving operation in which decrease of autofluorescent brightness of the soybean tissue was observed by autofluorescent stereo microscopy. However, the tissue microstructure visualized by the SEM was not obviously changed in the autoclaving process. As a result, it seemed that some compositions, which should influence hardness and autofluorescent properties of a soybean seed, were eluted from the tissue by the autoclaving operation. Shrinkage of an internal structure in a cell matrix, which should be resulted from protein decompositions by a protease reaction, was observed during fermenting and aging processes. As a result, a gap in a cell matrix increased and it was thought that the gap should also have relations with a slight decrease of hardness of sample soybeans. An observation of microscopic structures of a soybean seed during Natto making process has potential for studying manufacture of Natto.
Many processing techniques have been developed to produce cooked rice packed under semiaseptic condition (here in after called semi-aseptic cooked rice) with less microbial spoilage, better taste and higher quality. In this study, effect of heat-resistant microorganisms in rice on commercial sterility of cooked rice was examined using pH-controlled rice. Improvement method of cooking process was investigated to upgrade the storage stability of cooked rice with microorganisms based on the concept of commercial sterility for the retort pouch foods. The growth of Bacillus subtilis isolated form brown rice was not inhibited on rice adjusted pH 4.6 and pH 5.0 at 30°C. To ensure the commercial sterility of semi-aseptic cooked rice, the isolated B. subtilis strain should be inactivated in heat cooking process. The conditions of heat cooking was investigated for semi-aseptic cooked rice adjusted pH 4.6 or pH 5.0 to ensure equivalent eating quality to conventional process and commercial sterility against B. subtilis. The optimum cooking condition for the rice of pH 4.6 was 18 minutes with 98°C and that for the rice of pH 5.0 was 14-16 minutes with 105°C or 9-11 minutes with 110°C.
In our previous report , we have proposed the Ambient Temperature Slide Method (ATS Method) as a rational way to estimate the central temperature of individually packed foods during retort sterilization. In this paper, we aimed to get new knowledge by specifically comparing ATS Method with simple One-Dimensional Finite-Difference Method (s-OFD Method) that was improved for the practical use of a conventional method using numerical calculation in order to solve the heat conduction equation (One-Dimensional Finite-Difference Method (OFD Method) ) . From the results of the experiments, it was clear that the Outside Film Heat-Transfer Coefficient h showed a smaller value than the expected one in the OFD Method and so surface heat transfer resistance is so large that it cannot be ignored. Because of this reason, it was thought to have been the obstacle for accurate estimating of the central temperature of foods. When we did parameter-fitting, ATS Method proved to be more than twice as good as the s-OFD Method in convergent accuracy and it was also good in convective foods as well as conductive foods. And, the F-value errors in simulation by using parameters obtained by parameter-fitting in the case of 4 food samples showed only one fifth of the value calculated on the s-OFD Method, it means that the convergent accuracy of ATS Method is five times better than the s-OFD Method. ATS Method showed approximately “1” in the ratio of thermal diffusivity for conductive foods. This result may indicate the possibility in simple theoretical caluculation of parameter of heat transfer τ. From these results, ATS Method was thought to be several times better than the s-OFD method that is a conventional method and an improving one of OFD Method in estimating for the central temperature of foods.
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