Quantification of bacterial chemotaxis in porous media using magnetic resonance imaging

Bacterial chemotaxis has the potential to enhance biodegradation of organic contaminants in polluted groundwater systems. However, studies of bacterial chemotaxis in porous media are scarce. In this study we use magnetic resonance imaging (MRI) for the noninvasive measurement of changes in bacterial-density distributions in a packed column at a spatial resolution of 330 microm as a function of time. We analyze both the diffusive and the chemotactic behavior of Pseudomonas putida F1 in the presence of the chemical stimulus trichloroethylene (TCE). The migration of motile bacteria in experiments without TCE was described using an effective motility coefficient, whereas the presence of TCE required addition of a nonzero chemotactic sensitivity coefficient, indicating a significant response to TCE. The need for a chemotactic sensitivity term was justified by a test for statistical significance. This study represents the first quantification of bacterial chemotactic parameters within a packed column. For conditions under which chemotaxis occurs in porous media, it may potentially be exploited to significantly improve rates of in situ pollutant biodegradation in the subsurface environment, particularlyfor pollutants dissolved in water trapped in low-permeability formations or lenses.     

Moisture migration by magnetic resonance imaging during eggplant drying: a preliminary study

The paper investigated the effect of hot‐air drying (50, 60 °C) on the physical properties of cylindrical eggplant samples. Drying kinetics, water profiles along longitudinal and transversal sample sections through nuclear magnetic resonance imaging (MRI) and volumetric shrinkage were determined. During the drying process at 50 °C, the volume of removed water was found lower than the reduction in sample volume, while at 60 °C it was higher. MRI showed that the water migration mainly occurs transversally than longitudinally. The curves of mass water loss obtained by both the standard weighting method and MRI showed conformity. Experimental data of moisture ratio and of shrinkage volume were fitted using empirical models available in the literature. This preliminary study showed that the nondestructive MRI technique offers the possibility to study water distribution in food during drying processes. The quantitative moisture distribution maps allow future development and verification of models for prediction of mass transport phenomena in foods during drying.     

Nanoencapsulation systems to improve solubility and antioxidant efficiency of a grape marc extract into hazelnut paste

Encapsulation of a phenolic grape marc extract to enhance its lipid solubility and antioxidant efficiency for application as a natural preserving agent of hazelnut paste was investigated. Three nanoemulsion based encapsulation systems were tested: an oil/water nanoemulsion; a powder obtained by maltodextrin-assisted spray-drying of the previous and an ethanol/solid–lipid nanoemulsion (the third also applied to resveratrol for comparison). All the samples were mixed with hazelnut paste at different phenolic concentrations (from 1200 to less than 10 ppm of gallic acid equivalents for the original and encapsulated extracts, respectively). An accelerated shelf-life test at 60 °C was carried out until 59 and 98 days (for the original and encapsulated extracts, respectively) with peroxides value monitoring. Paste oxidation followed a first-order kinetics model and was significantly inhibited by extract addition. Encapsulation improved phenolic efficiency against lipid oxidation, by increasing extract dispersability in the paste and preserving the antioxidant activity, with the oil/water nanoemulsion resulting as the best system.     

Investigation of nanoparticle transport inside coarse-grained geological media using magnetic resonance imaging

Quantifying nanoparticle (NP) transport inside saturated porous geological media is imperative for understanding their fate in a range of natural and engineered water systems. While most studies focus upon finer grained systems representative of soils and aquifers, very few examine coarse-grained systems representative of riverbeds and gravel based sustainable urban drainage systems. In this study, we investigated the potential of magnetic resonance imaging (MRI) to image transport behaviors of nanoparticles (NPs) through a saturated coarse-grained system. MRI successfully imaged the transport of superparamagnetic NPs, inside a porous column composed of quartz gravel using T(2)-weighted images. A calibration protocol was then used to convert T(2)-weighted images into spatially resolved quantitative concentration maps of NPs at different time intervals. Averaged concentration profiles of NPs clearly illustrates that transport of a positively charged amine-functionalized NP within the column was slower compared to that of a negatively charged carboxyl-functionalized NP, due to electrostatic attraction between positively charged NP and negatively charged quartz grains. Concentration profiles of NPs were then compared with those of a convection-dispersion model to estimate coefficients of dispersivity and retardation. For the amine functionalized NPs (which exhibited inhibited transport), a better model fit was obtained when permanent attachment (deposition) was incorporated into the model as opposed to nonpermanent attachment (retardation). This technology can be used to further explore transport processes of NPs inside coarse-grained porous media, either by using the wide range of commercially available (super)paramagnetically tagged NPs or by using custom-made tagged NPs.     

Applications of magnetic resonance imaging in food science

The physical and chemical changes that occur in foods during growth, harvest, processing, storage, preparation, and consumption are often very difficult to measure and quantify. Magnetic resonance imaging (MRI) is a pioneering technology, originally developed in the medical field, that is now being used in a large number of disciplines to study a wide variety of materials and processes. In food science, MRI techniques allow the interior of foods to be imaged noninvasively and nondestructively. These images can then be quantified to yield information about several processes and material properties, such as mass and heat transfer, fat and ice crystallization, gelation, water mobility, composition and volume changes, food stability and maturation, flow behavior, and temperature. This article introduces the fundamental principles of MRI, presents some of the recent advances in MRI technology, and reviews some of the current applications of MRI in food science research.     

Detecting vegetable oil adulteration in hazelnut paste (Corylus avellana L.)

The possibilities of detecting hazelnut paste adulterated with refined and non-refined vegetable oils have been studied. Research was focussed mainly on peanut, high oleic-acid sunflower, corn and soybean oils which have a similar composition to hazelnut oil. The analytical procedures to detect fatty acid (FA), triacylglycerol (TAG) and tocopherol profiles as indicators of adulteration were determined. The better indicators experimentally determined were seven FA (palmitic, stearic, linoleic, linolenic, arachidonic, behenic and lignoceric acids) and different TAG with three unsaturated FA (the code letters used for FA are: P = C_16:0; S = C_18:0; O = C_18:1; L = C_18:2;; L_n = C_18:3) (LLL_n, LLL and OOO), two unsaturated FA (POL, PLL and SOO), and one unsaturated FA (PPL). As expected, when refined vegetable oils were added to hazelnut paste, the increment of stigmasta-3,5-diene allowed detection at levels of 2% oil added. Limits of detection were measured using standard and adulterated hazelnut with different amounts of non-refined vegetable oils added (5%, 10%, 20% and 30%). The distribution of tocopherols and tocotrienols is highly useful, except in the case of added sunflower oil. The differences between the experimental and theoretical values of the TAG with equivalent carbon number (ΔECN) of 42 does not improve the detection limit of hazelnut paste adulterated with peanut or sunflower oils. Similarly, tocopherols usually added to refined vegetable oils as an antioxidant were also determined.     

Analysis of column tortuosity for MnCl2 and bacterial diffusion using magnetic resonance imaging

Subsurface bacteria often have to travel significant distances through tortuous porous media for purposes of groundwater remediation. In modeling such processes, motile bacteria are often represented as suspended colloids, ignoring their individual swimming or diffusive properties. In fact, bacterial migration is much more profoundly affected by the presence of porous media than is that of a chemical contaminant. In this study, we use magnetic resonance imaging (MRI) to perform noninvasive measurements of changes in bacterial concentration distributions across a packed column at a spatial resolution of 330 microm as a function of time. We analyze the diffusive behavior of Pseudomonas putida F1 under static conditions and compare that behavior to the diffusion of a chemical solute and of Escherichia coli NR50. Results indicate that P. putida cells experience a column tortuosity 50 times higher than that predicted from solute diffusion experiments. E. coli cells, which display shorter swimming run lengths in bulk solution than P. putida, seem to be less affected by the constricted pore space. Knudsen diffusion, or reductions in run length because of interactions between the diffusing bacteria and the porous media, may help to explain some of this discrepancy.     

Analysis of bacterial random motility in a porous medium using magnetic resonance imaging and immunomagnetic labeling

In this study, we demonstrate the application of immunomagnetic labeling and magnetic resonance imaging (MRI) for the noninvasive visualization of changes in bacterial density distributions as a function of time in a water-saturated porous medium. Magnetite particles (50-60 nm diameter) were attached via a monoclonal antibody to the surface' of Escherichia coli K12 NR50 cells. The cells maintained their motility after labeling, and the presence of the magnetite did not significantly alter cell swimming speed. Diffusive migration for both motile and nonmotile E. coli through a porous medium with a particle-diameter distribution of 250-300 microm was compared. The movement of the nonmotile cells was described by an effective random motility coefficient consistent with Brownian diffusion of a nonmotile colloid. An effective coefficient determined a priori from bacterial motility in an aqueous medium and properties of the porous medium adequately described the movement of the motile cells. The ability to noninvasively visualize bacterial concentrations within an opaque porous medium in real time provides researchers with a powerful tool for studying bacterial transport in porous media. This is important for understanding the impact of bacterial transport on remediation strategies for environmental cleanup of polluted groundwater.     

Heating and cooling of hazelnut paste in alternate blades scraped surface heat exchangers

This paper extends a former analysis on the thermal behavior of a new kind of scraped surface heat exchanger operated in laminar regime to treat hazelnut paste, a high viscous non-Newtonian fluid largely adopted in the Italian confectionary industry. This unit, named A-SSHE, presents an alternate arrangement of the scraping blades that allows doubling the exchanger thermal efficiency respect to conventional SSHE with continuous blades, mainly thanks to backmixing phenomena.     

Explaining tolerance for bitterness in chocolate ice cream using solid chocolate preferences

Chocolate ice cream is commonly formulated with higher sugar levels than nonchocolate flavors to compensate for the inherent bitterness of cocoa. Bitterness, however, is an integral part of the complex flavor of chocolate. In light of the global obesity epidemic, many consumers and health professionals are concerned about the levels of added sugars in foods. Once a strategy for balancing undesirable bitterness and health concerns regarding added sugars has been developed, the task becomes determining whether that product will be acceptable to the consumer. Thus, the purpose of this research was to manipulate the bitterness of chocolate ice cream to examine how this influences consumer preferences. The main goal of this study was to estimate group rejection thresholds for bitterness in chocolate ice cream, and to see if solid chocolate preferences (dark vs. milk) generalized to ice cream. A food-safe bitter ingredient, sucrose octaacetate, was added to chocolate ice cream to alter bitterness without disturbing other the sensory qualities of the ice cream samples, including texture. Untrained chocolate ice cream consumers participated in a large-scale sensory test by indicating their preferences for blinded pairs of unspiked and spiked samples, where the spiked sample had increasing levels of the added bitterant. As anticipated, the group containing individuals who prefer milk chocolate had a much lower tolerance for bitterness in their chocolate ice cream compared with the group of individuals who prefer dark chocolate; indeed, the dark chocolate group tolerated almost twice as much added bitterant in the ice cream before indicating a significant preference for the unspiked (control) ice cream. This work demonstrates the successful application of the rejection threshold method to a complex dairy food. Estimating rejection thresholds could prove to be an effective tool for determining acceptable formulations or quality limits when considering attributes that become objectionable at high intensities.     

Characterization of NAPL source zone architecture and dissolution kinetics in heterogeneous porous media using magnetic resonance imaging

A direct visualization method using magnetic resonance imaging (MRI) was developed to characterize sand grain size distribution, nonaqueous phase liquid (NAPL) source zone architecture, and aqueous flowpaths in a three-dimensional (3-D) flowcell (26.5 cm x 10.5 cm x 10.5 cm) packed with a heterogeneous distribution of five different sand fractions. All images were acquired at a resolution of 0.1875 cm x 0.1875 cm x 0.225 cm. A 1H image of pore water resolved the heterogeneous permeability field; grain size differences as small as 0.1 mm could be distinguished. A time series of 1H images of water doped with the paramagnetic tracer MnCl2 were acquired and used to obtain voxel-scale breakthrough curves. Water preferentially flowed through coarse sands before NAPL release. After NAPL release, the flow bypassed NAPLzones, and bypassing was more evident for high NAPL saturation zones. A time series of 19F images of NAPL were acquired and used to determine voxel-scale NAPL saturation (Sn) during dissolution. Results show that 93% of NAPL mass was in the coarsest sand, most NAPL was trapped as pools and not as residual ganglia, NAPL saturation increased with depth, and the NAPL dissolution front moved vertically from the top to the bottom of the flowcell during the first 170 pore volumes of waterflushed. NAPL component effluent concentrations initially increased due to the development of flow in zones with decreasing NAPL saturation. Flowpath images suggest that this occurs as NAPL transitions from pools (Sn > 0.15) to residual ganglia. The results highlight the importance of flow bypassing and provide the opportunity to develop more accurate NAPL dissolution models.     

Moisturization processes in living human skin studied by magnetic resonance imaging microscopy

Magnetic resonance imaging is a non-invasive, non-destructive and chemically specific imaging method widely used in medicine to reveal information about both tissue structure and function. It can measure water in tissue, but it has been difficult to achieve the necessary sensitivity and resolution when applying it to studies of the dry, thin stratum corneum. In this paper the use of magnetic resonance imaging to image the outer layers of the skin with a resolution of 0.06 mm is reported. Configuring the magnetic resonance imaging method in this way has made it possible for the first time to actually 'see'directly the moisturization in the stratum corneum. It is no longer necessary to rely upon methods which can only show side-effects of moisturization, such as changes in the appearance of the skin cells. As magnetic resonance imaging is harmless, it can be used repeatedly on the same skin and so produce a series of stills, or a time-lapse video, clearly showing the actual process of moisturization and related phenomena. The behaviour of skin has been observed during both hydration and dehydration; the two processes follow different time courses. Two layers have been observed in the stratum corneum, which appear to be different when the skin is hydrated.
For the first time the actual surface of normal skin has been revealed on magnetic resonance images.     

Investigation of the behaviour of chitosan microparticles as pH responsive hydrogels in the gastro-intestinal tract using magnetic resonance imaging

The objective of this research was to determine whether chitosan microparticles could be developed as potential satiety enhancing ingredients by investigating their swelling behaviour in the gastro-intestinal tract using magnetic resonance imaging (MRI). Previous work undertaken using a covalently cross-linked composite of chitosan and bovine serum albumin (BSA) showed this system swells in gastric conditions in vitro (Butler, Clark, & Adams, 2006). This paper describes the preparation and characterisation of chitosan/BSA microparticles cross-linked using 25 mM and 100 mM glutaraldehyde (GDA). 1.5% chitosan/15% BSA microparticles cross-linked with 25 mM GDA swell by 100% in simulated gastric conditions. We found an experimental correlation between the transverse NMR relaxation time, T₂, and swelling of the microparticles in vitro. Our study of four volunteers showed swelling of these microparticles in the human stomach, observed from increases in T₂ of the microparticles using non-invasive MRI. As such, our initial results, with 4 volunteers, suggest that this system could be used as a potential satiety enhancing agent in vivo as we would expect it to provide gastric distension due to swelling at low pH. Further studies with more volunteers would be necessary to confirm our initial findings.     

Monitoring dry-curing of S. Daniele ham by magnetic resonance imaging

S. Daniele hams were collected at different stages during dry-curing and submitted to magnetic resonance imaging (MRI) according to the acquisition Spin-Echo sequences T1 and T2. The intensity of the MR signals in the images of the Semimembranosus, Semitendinosus, Rectus femoris and Biceps femoris muscles of the hams was computed and expressed in grey levels. Muscles were also submitted to traditional analyses, including a_w, soluble solids, sodium chloride, total and water soluble nitrogen. T1 and T2 MR signals well described the evolution of the phenomena occurring in the different muscles during dry-curing. MR signal acquired in T2 mode well correlated with traditional indicators in Semitendinosus, Rectus femoris and Biceps femoris muscles. Predictive models estimating the value of a_w, moisture, salt content and proteolysis extent on the basis of the MR signal intensity were proposed.     

On-line observation of dough fermentation by magnetic resonance imaging and volumetric measurements

The fermentation of bread and cake dough was monitored on-line by two types of volumetric measurements and by magnetic resonance imaging (MRI). The volumetric measurements enabled independent determination of the actual dough volume and the amount of carbon dioxide that permeated out of the dough. MRI allowed us to obtain an insight into the developing dough and to observe the pore structure during proofing. Due to the non-destructive and non-invasive character of the methods, no sample preparation was necessary, and the fermentation process was not influenced by the measurements. Both methods provided results that were in accordance with each other. The data were used to derive formal reaction-kinetic data for the course of the fermentation process in bread and cake doughs.     

Quantitation by magnetic resonance imaging of heating of commercial baby foods in glass jars

This study demonstrates how magnetic resonance imaging can be used to quantitate the heating of commercially available baby foods as sold in glass jars either ‘on‐line’ during immersion in warmed water in the scanner's magnet, or ‘off‐line’ following microwave heating. The internal temperature distribution can be measured in 2‐ or 3‐dimensions with a precision of ±1.5 °C compared with fibre optical thermo‐probe measurements. Illustrative examples include jars of Heinz ‘Banana & Apple’, Sainsbury's ‘Organic Banana Rice Pudding’ and Cow & Gate ‘Organic Roasted Vegetable Lasagne’. Localised thermal lags induced by pieces of vegetable in the lasagne were observed during on‐line immersion heating. Importantly, the spatially heterogeneous heating by microwaves demonstrates the need for strong warnings about using microwave ovens for heating baby foods.     

Monitoring changes in feta cheese during brining by magnetic resonance imaging and NMR relaxometry

Magnetic resonance imaging (MRI) and NMR relaxometry were used to monitor changes in feta cheese during 169 h of brining at 4.8%, 13.0% and 23.0% salt solutions. Image and relaxation data were acquired to study salt uptake and water loss due to dehydration of cheese during brining. Saturation recovery and Carr-Purcell-Meiboom-Gill (CPMG) sequences were used to determine the longitudinal relaxation (T₁) and the transverse relaxation (T₂) times, respectively. Signal intensities of T₂ weighted images decreased during 169 h of brining. An excellent linear correlation between the average signal intensity and the water content was obtained (R² = 0.984). The T₁ values of cheese brined at 4.8% were almost constant but T₁ values decreased for both 13.0% and 23.0% salt brined cheeses. Analysis of the CPMG decays gave relaxation spectra containing two components which decreased during brining. The short component T_2a was highly correlated with salt content (R² = 0.974). Results showed that NMR and MRI can be used to follow salt uptake and changes in water content in cheese during brining.     

Soil wettability as determined from using low-field nuclear magnetic resonance

The molarity of ethanol droplet and water drop penetration time methods are commonly used to determine soil wettability because these tests are quick and easy to perform. However, these tests do not provide reproducible results on the same sample. Low-field nuclear magnetic resonance (NMR) is shown as an alternative tool to determine soil wettability. Addition of small amounts of water in dry wettable porous media produces predominant amplitude peaks at transverse relaxation times (T2) of 100 ms or less while addition of water in dry water-repellent porous media with the same pore structure produce predominant amplitude peaks at T2 values near 1000 ms. The geometric mean of T2 (T(2gm)) from water-repellent samples immediately after the addition of water is greater than 1000 ms, which is close to that of bulk water, while T(2gm) from wettable samples immediately after the addition of water is significantly less than 1000 ms. Measurements over time show that water-repellent samples eventually reach the same equilibrium end point as its corresponding wettable sample when continually exposed to water. This paper will show that NMR can be used to formulate a screening criterion for quickly determining wettability. The advantage of using NMR is that the results are reproducible provided the sample is prepared and analyzed in a systematic manner.