Mika Fukuoka

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.

Synthesis of L-threo- and L-erythro-[1-13C, 2,3-2H2]amino acids: novel probes for conformational analysis of peptide side chains

An efficient and convenient route for the preparation of L-threo- and L-erythro-[1-l3C, 2,3-2H2]amino acids 5 as probes for the conformational analysis of peptide side chains by NMR spectroscopy is described. Stereoselective incorporation of deuterium into the α,β-positions of amino acid 5 was accomplished by catalytic deuteriation of dehydroamino acid derivatives 1 and 2 followed by a combination of enzymic optical resolution and the racemization at the 2-position. Using the doubly labelled amino acids, it was possible to obtain vicinal coupling constants between carbonyl carbon and prochiral β-protons, J(13C1–1Hβ1) and J(13C1–1Hβ2), through 13C NMR spectroscopy alone. We also demonstrate the determination of the fractional populations of rotamers in respect of the Cα–Cβ bond of the amino acids using the measured coupling constants.

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.

Recent advances in characterization of foods using nuclear magnetic resonance (NMR)

Publisher Summary This chapter describes nuclear magnetic resonance (NMR) spectroscopy with an emphasis on one of the most important recent developments in NMR: the methods, which concern the application of a linearly varying magnetic field, known as a field gradient. NMR has two very important advantages over other physicochemical methods when applied to food science and engineering. These are that it is noninvasive and that information may be obtained over a wide variety of length and time scales. Because of these two properties, NMR is well suited to probe the complexities of heterogeneous systems, such as food. Pulsed-field gradient NMR and NMR imaging are still in their early stages of development. Rapid development in methods and apparatus is expanding the field for potential applications. It is not by food industry but by medicine and pharmaceuticals and biotechnology industries that many of the new developments in NMR technology have been financially supported. NMR has a merit of particular importance to medical applications: it allows obtaining the internal structure of biological systems nondestructively and noninvasively. Its greatest potential lies in its ability to provide NMR spectroscopic information from spatially resolved regions within the image. Because NMR signal is sensitive to chemical environment, molecular dynamics, and position in space, obtained signal data contain a mixture of these types of information. A separation of these types of information often requires detailed analysis using appropriate mathematical model. Improvement in the methods and apparatus of NMR may help in using more precise mathematical models, which are helpful for the separation.

Moisture Diffusion in Fresh and Dehydrated Fish Flesh Measured by PFG-NMR

Diffusion coefficient of moisture in codfish was measured using PFG–NMR. Intact as well as processed (minced with and without NaCI, fresh and heated, freeze-dried) sample were examined. The effect of diffusion time ranging from 28 ms to 100 ms was examined. Intact flesh showed unrestricted feature of moisture diffusion while minced flesh showed restricted moisture diffusion. Dependence of moisture content on diffusion coefficient was obtained.