Hisahiko Watanabe

The change of moisture distribution in a rice grain during boiling as observed by NMR imaging

Abstract The change of moisture distribution in a grain of rice during boiling was observed using the nuclear magnetic resonance (NMR) transverse relaxation time (T2) imaging method and the factors which governed the cooking process were examined. Partly cooked samples were taken at various intervals and the moisture profile in a slice perpendicular to the long axis of the grain was obtained. Since the change of moisture profile during cooking in a cellulasetreated rice grain showed no remarkable difference from that of a non-treated one, it suggested that the non-cellulase-treated wall of endosperm cells had little effect on suppressing water migration. A one-dimensional moisture profile, which was constructed from an experimentally obtained two-dimensional moisture map, was simulated using a mathematical model in which water percolated through a starch cylinder by diffusion and was limited by gelatinization. Although the calculation successfully simulated the shape of the moisture profile, it showed a delay in the rise of the moisture. The cause of this delay is not yet known.

Determination of the terminal extent of starch gelatinization in a limited water system by DSC

Abstract Starch granules are gelatinized rapidly to reach a specified extent of gelatinization within 1 or 2 min. This upper limit to the extent of gelatinization may be termed the terminal extent of gelatinization (TEG) which depends on temperature and moisture content. TEG in wheat starch/water system (moisture content 0.54–3.0 g water/g starch) was measured by differential scanning calorimetry (DSC) in the temperature range of 60–100 °C. An empirical equation which enables the prediction of TEG as a function of temperature and moisture content was obtained.

An application of magnetic resonance imaging to the real time measurement of the change of moisture profile in a rice grain during boiling

Abstract The change of moisture distribution in a rice grain during boiling was observed in real-time by NMR T 2 imaging. A series of one-dimensional proton images along a lateral line (through the cross section) perpendicular to the long axis of the grain was obtained every two minutes using a CPMG multi-spin-echo method. The series of images was analyzed to give the apparent T 2 profile, which was then converted into the moisture content profile. The rise in moisture profile during boiling obtained by real-time observation was found to be unexpectedly rapid when it was compared with that reported previously using a non-real-time method for samples which were quenched after boiling for selected periods of minutes. The error in the NMR imaging method caused by the effect of diffusion on the apparent T 2 was fully analyzed using the pictorial phase diagram method.

A new non-Fickian diffusion model for water migration in starchy food during cooking

When a starchy food such as a rice grain or a strand of noodle is boiled, a high moisture region is generated at the surface spreading inward, producing a low moisture core. The characteristic features of the change of moisture profile were recently observed by nuclear magnetic resonance imaging (MRI). However, the profile cannot be described by any existing mathematical model based on the principle that water molecules are driven by the gradient of moisture content. In this paper, a new mathematical model is proposed using a new concept, water demand (WD). In this model, migration of water is driven by the gradient of WD, which is defined as the difference between the ceiling moisture content and the existing moisture content. This model is demonstrated to have a potential to describe the characteristic features of the change of moisture profile in starchy food during boiling.

The rate of starch gelatinization as observed by PFG-NMR measurement of water diffusivity in rice starch/water mixtures

Abstract The gelatinization rate of rice starch was studied by observing the water diffusivity measured by a PFG (Pulsed-Field-Gradient)-NMR method. A rice starch/water mixture in glass capillary tubes was heated and cooled in a stepwise manner. The water diffusivity in these samples decreased as heating time increased. This was recognized as the increase in the amount of carbohydrate polymer dissolved in the aqueous phase during heating. Consequently, the measured water diffusivity was converted into the moisture content in the dissolved polymer solution. The time course of changes in this moisture content was approximated as a first-order process, and a rate constant in the order of 10 −2 s −1 was obtained for 66–80 °C. This value is comparable to that in the literature measured by a DSC isothermal method, while those measured by other methods such as flow consistency and gravimetric methods were 100-fold smaller.

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.

Measurement of moisture diffusion in foods using pulsed field gradient NMR

Abstract Moisture diffusion coefficients in solid foods have traditionally been measured using gravimetric methods and tracer methods. Pulsed field gradient NMR (PFG-NMR) is an alternative means of obtaining more reliable data. PFG-NMR can detect molecular migration over several microns, of the order of the cell size, and PFG-NMR experiments have been used to detect the reflection of molecules at barriers. Such diffusion data provide useful information on food microstructure. PFG-NMR can be incorporated into NMR imaging experiments to provide non-invasive real-time measurements of localized diffusion.

Moisture diffusion in a dry soybean seed measured using pulsed-field-gradient NMR

Abstract Moisture diffusion coefficient in a dry soybean seed was measured by a pulsed field gradient NMR method using stimulated echoes. A constant diffusion coefficient of 4·3 × 10 −10 m 2 s −1 was obtained for diffusion times ranging from 18·5 ms to 28·5 ms. This value is 10 times larger than literature values measured by a gravimetric method of seed hydration, and is 100 times larger than that calculated using absorption and desorption data. With the aid of NMR imaging, it was revealed that a dry soybean seed had considerable freely movable water which was centred at the intercotyledon face surrounded by an oil layer. The discrepancy in diffusion coefficients between those measured by NMR and by the gravimetric method is discussed. When the diffusion time was extended over 38·5 ms to 113 ms, a clearly restricted feature of diffusion was observed.

Fracture stress of fish meat and the glass transition

Abstract Freezing a high moisture food may involve the crystallization of pure water and therefore concentrate the solute, which sometimes forms a concentrated amorphous solution (CAS). The CAS may be formed via hot air drying as well, although most hot air dried foods available on the market are porous and/or in powder form and are inconvenient for use in fracture tests. In this paper, the traditional Japanese dried food ‘katsuo-bushi’, a highly smoked, dried fillet of bonito fish meat (which can be regarded as a CAS in itself) was used as samples to measure the compressive fracture stress. The compressive fracture stress of 0% moisture Katsuo-bushi was found to be constant at temperatures between 25 °C and −196 °C, and this value was comparable to that of 0% moisture CAS of completely frozen bonito meat estimated using a simple model for a frozen food. On the other hand, fracture stress of katsuo-bushi with 15–20% moisture changed greatly at temperatures between 0 °C and −90 °C, showing the feature of yielding. The temperature of brittle-ductile transition was different from the glass transition temperature as defined by DSC.

An on-line method for predicting freezing time using time/temperature data collected in the early stages of freezing

Abstract Existing methods of estimation of freezing time require data on thermal properties of the product and any relevant heat transfer coefficients. This paper describes a new procedure for estimating freezing time; a procedure that does not require the knowledge of thermal data of the food being frozen. This procedure collects time/temperature data from the early stages of cooling, analyzes these data to determine system parameters associated with the heat conduction equation and predicts the time/temperature profile in the remainder of the freezing process using these system parameters. This system has been validated via experiments on freezing fish meat as well as wheat flour dough.