B.P. Hills

The distribution of water in native starch granules—a multinuclear NMR study

The microscopic distribution and dynamic state of water in native potato, maize and pea starch granules are investigated with NMR relaxometry and diffusometry. Besides extra-granular water, three water populations can be identified inside native potato starch granules. These are assigned to water in the amorphous growth rings; water in the semi-crystalline lamellae and “channel water”, which is located in the hexagonal channels within the B-type amylopectin crystals. The first two water populations are orientationally disordered and exchange with each other on a millisecond timescale at 290 K. NMR diffusometry shows that the water in packed granule beds is undergoing translational diffusion in a 2-dimensional space, either in thin layers between granules and/or in amorphous growth rings within the granules. The “channel water” is uniquely characterised by a 1 kHz deuterium doublet splitting and is in slow exchange with water in the other compartments on the NMR timescale. In the smaller maize granules all intra-granular water populations are in fast exchange and there is no evidence for “channel water” in the A-type crystal lattice. The NMR water proton and deuterium data for pea starch are consistent with a composite A and B-type crystal structure. q 2000 Elsevier Science Ltd. All rights reserved.

A Fourier transform infrared study of water-head group interactions in reversed micelles containing sodium bis(2-ethylhexyl) sulfosuccinate (AOT)

Abstract Fourier transform infrared spectroscopy has been employed to study the state of water and water—head group interactions in AOT aggregates or microemulsions in n-heptane. Isotopic dilution of water (4% D2O and in H2O) has been used to monitor the uncoupled ν(OD) band of HOD as a function of W0 (the number of water molecules per head group). It is found that the feature always consists of a single-band profile and there is no evidence of coexisting multiple water species in these systems (on the vibrational time scale). By detailed examination of ν(SO) and ν(CO) bands of the head group it is found that up to W0 = 6 (severely perturbed) water molecules are bound closely to the sulfonate and Na+ ions at the water/organic interface. Beyond this point all the water molecules seem to have a similar vibrational relaxation rate but there are still gradual structural and electronic changes as the water molecules move farther away from the first hydration shell. At values of W0 higher than 12 there is some evidence that the water molecules are similar to those in the bulk, but up to 20 water molecules per head group are probably needed to form well-defined reversed micelles in these systems.

Assignments of proton populations in dough and bread using NMR relaxometry of starch, gluten, and flour model systems.

Starch-water, gluten-water, and flour-water model systems as well as straight-dough bread were investigated with (1)H NMR relaxometry using free induction decay and Carr-Purcell-Meiboom-Gill pulse sequences. Depending on the degree of interaction between polymers and water, different proton populations could be distinguished. The starch protons in the starch-water model gain mobility owing to amylopectin crystal melting, granule swelling, and amylose leaching, whereas water protons lose mobility due to increased interaction with starch polymers. Heating of the gluten-water sample induces no pronounced changes in proton distributions. Heating changes the proton distributions of the flour-water and starch-water models in a similar way, implying that the changes are primarily attributable to starch gelatinization. Proton distributions of the heated flour-water model system and those of fresh bread crumb are very similar. This allows identifying the different proton populations in bread on the basis of the results from the model systems.

A proton NMR relaxation study of the gelatinisation and acid hydrolysis of native potato starch

The effect of acid hydrolysis (Lintnerisation) and the thermal gelatinisation on the dynamic state of starch and the microscopic distribution of water within native potato starch granules is investigated with proton NMR relaxometry. The NMR relaxation data show several dynamic states of the amylose and amylopectin chains and clearly identify the melting transition during thermal processing. The Lintnerisation process is found to follow first-order kinetics and to shift and broaden the melting transition. The unique value of NMR relaxometry for monitoring the processing response of starch granules is discussed.

Quality Assessment of Horticultural Products by NMR

The potential for developing NMR as an on-line sensor of the internal quality of fruits and vegetables is discussed. The literature on the NMR of horticultural products is first surveyed for potentially useful correlations between NMR characteristics and internal quality factors in commercially important harvested products. This is followed by discussions on the cellular origins of these correlations and of the technical problems to be overcome in the development of a commercial on-line NMR sensor.

Applications of Low-Field NMR to Food Science

Publisher Summary This chapter presents the developments in low-field nuclear magnetic resonance (NMR) that have the potential of revolutionizing quality control in the food sector. This includes new NMR devices such as ex situ NMR probes, on-line sensors, new ultrafast analytical methods, and multidimensional approaches to relaxometry and diffusometry that dramatically increase the information content compared to traditional 1D relaxation or diffusion measurements. It is also clear that much research remains to be done to take these novel approaches to the point where they cease to be feasibility studies undertaken by NMR specialists and end up as user-friendly tools in the hands of food scientists and quality controllers. Besides food applications, it is also obvious that many of the developments such as low-cost NMR sensors and Halbach NMR have the potential for spreading NMR and MRI technology throughout other industries, including those in the pharmaceutical, construction, and energy sectors. Probing food functionality with NMR in real time therefore presents an almost unique challenge where extremely complex soft-solid materials are being probed by a uniquely subtle and powerful technique.

Food processing: An MRI perspective

Abstract The past few years have seen a rapid increase in the application of magnetic resonance imaging (MRI) to foods. This is creating exciting new opportunities for optimizing food process design and also, at a more fundamental level, for understanding the mechanisms of both heat and mass transport in foods as well as the many factors contributing to food quality.

Radial NMR microimaging studies of the rehydration of extruded pasta

A novel NMR radial microimaging technique is used to image the ingress of water into extruded pasta during rehydration. It is shown that the rehydration is a non-Fickian diffusion process where the diffusion coefficient is strongly dependent on the local moisture content and where diffusion is accompanied by radial and length expansion. The simultaneous diffusion and expansion are modelled numerically for three types of extruded pasta, differing in the amounts of their constituent hard and soft wheat. It is found that increasing the amount of hard wheat shifts the diffusion closer to the limit of Case II Fickian diffusion where there is a sharp moving boundary between the unhydrated glassy state and the rehydrated gel. The potential of NMR radial microimaging for monitoring mass and heat transport during the processing of other food materials is discussed.

NMR studies of non-freezing water in cellular plant tissue

Abstract The distribution of water proton transverse relaxation times is used to monitor the amount and subcellular distribution of non-freezing water and ice in potato tissue. At subzero temperatures most of the non-freezing water is found to be associated with starch granules and cell wall material, and the amount of unfrozen water at each temperature has been determined. The potential of NMR relaxation techniques in food cryopreservation is discussed.

T1−T2 NMR correlation studies of high-pressure-processed starch and potato tissue

Two-dimensionalT1−T2 correlation spectroscopy is used to monitor the effect of high-pressure and microwave processing on the microscopic water distribution and starch chain dynamics in water-saturated packed beds of native A and B type starches. B type starches are shown to be more resistant to pressure treatment than A type starches. High-pressure-induced A type starch gels are also shown to be radically different from the corresponding thermally induced gel. Although the cell walls of raw potato are resistant to high-pressure damage, the tonoplast and plasmalemma membranes are disrupted by high pressure.