Kathryn L. McCarthy

Effect of extrusion cooking on functional properties and in vitro starch digestibility of barley-based extrudates from fruit and vegetable by-products.

Barley flour and barley flour-pomace (tomato, grape) blends were extruded through a co-rotating twin-screw extruder. The aim of the present study was to investigate the effects of die temperature, screw speed, and pomace level on water absorption index (WAI), water solubility index (WSI), degree of starch gelatinization, and in vitro starch digestibility using a response surface methodology. The selected extrudate samples were examined further using differential scanning calorimetry (DSC) and polarized light microscopy, respectively. The WAI of barley-pomace extrudates was affected by increasing pomace level. Temperature had significant effect on all types of extrudate but screw speed had significant linear effect only on barley and barley-grape pomace extrudates on degree of starch gelatinization. Although no gelatinization peak was detected, an endotherm was observed on all selected extrudates. In general, extrusion cooking significantly increased in vitro starch digestibility of extrudates. However, increasing level of both tomato and grape pomace led to reduction in starch digestibility.

Use of nuclear magnetic resonance imaging as a viscometer for process monitoring

Abstract Nuclear magnetic resonance imaging (NMRI or MRI) flow measurements and fundamental principles of capillary flow are combined to determine the shear viscosity of non-Newtonian fluids. Shear viscosity data are obtained over the shear rates inferred from the velocity profile measured using MRI. A single, 3 minute measurement consisting of a MRI-determined velocity profile (also referred to as a dynamic displacement profile or positiondisplacement correlation) and the corresponding pressure drop produces multiple shear viscosity-shear rate data points. This technique was applied to obtain shear viscosity-shear rate data for an aqueous carboxymethyl cellulose (CMC) solution. Good agreement is found between these data and those measured by conventional rotational rheometry. The potential applications of this MRI-based technique include on-line and in-line monitoring of the shear viscosity of single and multiphase non-Newtonian fluids that can be either opaque or transparent.

Reduction of Salmonella on Inoculated Almonds Exposed to Hot Oil

The heat resistance of Salmonella inoculated onto almonds was determined after immersion in hot oil. Whole almonds were inoculated with Salmonella Enteritidis PT 30 or Salmonella Senftenberg 775W and heated in oil. After heating, almonds were drained, transferred to cold tryptic soy broth, and mixed with a stomacher, and samples were plated onto tryptic soy and bismuth sulfite agars. Salmonella survivor inactivation curves were upwardly concave. Rapid reductions of 2.9, 3.0, or 3.6 log CFU/g for Salmonella Enteritidis were observed after 30 s of exposure to oil at 116, 121, or 127 degrees C, respectively. Thereafter, reduction occurred at a much slower rate. Similar reductions were observed at 127 degrees C for Salmonella Senftenberg. The Weibull model was used to predict 4- and 5-log reductions of Salmonella Enteritidis after 0.74 and 1.3 min at 127 degrees C, respectively. Neither Salmonella serovar could be recovered by enrichment of 1-g samples after almonds inoculated at 5 log CFU/g were exposed to oil at 127 degrees C for 1.5 min. Standard oil roasting times and temperatures that achieve acceptable kernel color and texture should result in much greater than 5-log reductions of Salmonella in almonds.

Magnetic resonance imaging of concentration and velocity profiles of pure fluids and solid suspensions in rotating geometries

Steady and unsteady state velocity and concentration profiles are presented for a 40% by volume suspension of polymethyl methacrylate (PMMA) spheres in polyalkylene glycol (PG). The profiles were obtained by using the noninvasive technique of nuclear magnetic resonance imaging (MRI) in three experimental geometries: coaxial rotating cylinders (i.e., for generating wide‐gap Couette flow), coaxial cylinders in which a straight flight rotates with the inner cylinder and spans the annulus between the surfaces, and a single screw extruder. Concentration profiles document the presence of particle migration from high shear to low shear regions in the concentric cylinder apparatus and in the extruder. However, concentration gradients across the gap in the straight‐flight cylinder are not exhibited, indicating the relative importance of mixing in that geometry. Velocity profiles for the pure PG fluid and for suspension flows which remain well‐mixed agree quantitatively with profiles predicted for Newtonian fluids....

Turbulent pipe flow studied by time-averaged NMR imaging : measurements of velocity profile and turbulent intensity

A time-averaged method to obtain quantitative measurements in turbulent flow by phase flow encoding NMR imaging is introduced. With this method time-averaged velocity profiles and turbulence intensities can be determined. Time-averaged velocity profiles for pipe flow of water driven by a constant pressure gradient at Reynolds numbers from 1200 to 9400 were visualized. A precise correlation between the pixel intensity of the time-averaged NMR flow image and the local turbulence intensity of the flow is derived. The measured turbulence intensities are in agreement with published data obtained using other experimental methods.

Application of NMR imaging to the study of velocity profiles during extrusion processing

Abstract Characterization of the flow of a food material through an extruder is essential to the design and control of extrusion systems. The complexity of flow and mixing patterns during extrusion presents a perplexing yet fascinating modeling challenge for food scientists. Flow velocity profiles can be evaluated non-invasively using NMR imaging to monitor the motion of a magnetically marked band of fluid across the diameter of the extruder; distortion of the band illustrates motion. This paper demonstrates the ability of the technique to provide qualitative and quantitative descriptions of flow patterns in a single-screw extruder.

Magnetic Resonance Imaging (MRI) and Relaxation Spectrum Analysis as Methods to Investigate Swelling in Whey Protein Gels

Effective means for controlled delivery of nutrients and nutraceuticals are needed. Whey protein-based gels, as a model system and as a potential delivery system, exhibit pH-dependent swelling when placed in aqueous solutions. Understanding the physics that govern gel swelling is thus important when designing gel-based delivery platforms. The extent of swelling over time was monitored gravimetrically. In addition to gravimetric measurements, magnetic resonance imaging (MRI) a real-time noninvasive imaging technique that quantified changes in geometry and water content of these gels was utilized. Heat-set whey protein gels were prepared at pH 7 and swelling was monitored in aqueous solutions with pH values of 2.5, 7, and 10. Changes in dimension over time, as characterized by the number of voxels in an image, were correlated to gravimetric measurements. Excellent correlations between mass uptake and volume change (R(2)= 0.99) were obtained for the gels in aqueous solutions at pH 7 and 10, but not for gels in the aqueous solution at pH 2.5. To provide insight into the mechanisms for water uptake, nuclear magnetic resonance (NMR) relaxation times were measured in independent experiments. The relaxation spectrum for the spin-spin relaxation time (T(2)) showed the presence of 3 proton pools for pH 7 and 10 trials and 4 proton pools for pH 2.5 trials. Results demonstrate that MRI and NMR relaxation measurements provided information about swelling in whey protein gels that can constitute a new means for investigating and developing effective delivery systems for foods.

Effect of Cocoa Butter Structure on Oil Migration

Oil migration from a high oil content filling into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from a cream filling system into cocoa butter, which provided a model for the behavior of chocolate-enrobed confectionery products with a soft, creamy center. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse sequence was used to acquire images with a 7.8 ms echo time and a 200 ms repetition time using a 1.03 T Aspect Imaging MRI spectrometer. Samples were prepared as a 2-layer model system of cocoa butter and model cream filling. Three methods were used to prepare the cocoa butter: static, seeded, and sheared. Samples were stored at 25 °C for a time frame of 56 d. The rate of oil migration was quantified by a kinetic expression based on the linear dependence of oil uptake by cocoa butter and the square root of the time. Samples showed distinctly different rates of oil migration, as evidenced by quantitative differences in the kinetic rate constant. Practical Application:  This work will be helpful to elucidate the influence of crystallization process and structural properties such as crystal nanostructure and crystal habit on the migration of oil through a crystalline fat matrix.

NMR velocity phase encoded measurements of fibrous suspensions

Nuclear magnetic resonance (NMR) imaging is a noninvasive technique that allows velocity measurement in systems where classical techniques are not suitable due either to opacity or the presence of a solid phase. NMR velocity phase encode measurements for the flow of fiber suspensions yield quantitative data for the average flow field in the suspensions and qualitative information on the microscopic nature of the flow. Bulk translational motion causes modulation of the phase of the sample magnetization which provides information on the average velocity field within the sample. Motions on spatial and time scales that are small relative to the measurement scales cause damping of the magnetization, as reflected by signal attenuation.

Flow profiles in a tube rheometer using magnetic resonance imaging

The velocity profiles of non-Newtonian fluids have been measured in a tube rheometer using magnetic resonance imaging (MRI). This experimental method of flow visualization is a non-invasive and non-destructive means to characterize flow behavior. The fluids examined in this paper are carboxymethylcellulose solution (CMC) and tomato juice. The velocity profiles obtained experimentally for the CMC solution by MRI were in good agreement with the analytical predictions. Velocity profiles obtained by imaging for tomato juice showed much greater dispersion of velocity than expected in the laminar flow regime