Life Sciences Commons^™

Some Effects Of Lipids On The Structure Of Foods, K. Larsson

Food Structure

The functional properties of different lipids in foods are demonstrated and related to the structure of lipid or lipid-water phases. On the basis of new X-ray data on the crystal structure of the B'-form and the a + B' transition in fats, the polymorphic transitions are considered as different lateral arrangements of triglyceride dimers. The physical properties of fat crystals can be explained from the structures, as well as possibilities to influence the polymorphic transitions.

Molecular interaction between polar lipids and proteins or starch is discussed, and the effect of the amylose-lipid inclusion complex on gelatinization temperature and water penetration …

Aspects Of Sample Preparation For Freeze-Fracture/Freeze-Etch Studies Of Proteins And Lipids In Food Systems. A Review, Wolfgang Buchheim

Food Structure

To select optimum specimen preparation methods and to correctly interpret freeze-fracture/freezeetch micrographs of food systems a detailed knowledge of the individual steps of preparation -- i.e. chemical fixation of samples, their cryoprotective pretreatment, cryofixation, freeze-fracturing and -etching, and replication -- and of their influence on the appearance of different constituents, especially proteins and lipids, is necessary. Food systems show great variation in composition, structure and especially in their content of water -- e.g. molecular and colloidal solutions, oil-in-water and water-in-oil emulsions, gels suspensions, semi-solid systems such as cheese, dried systems such as milk powders -- thus requiring a careful variation …

Microscopy In The Study Of Fats And Emulsions, J. M. Deman

Food Structure

Plastic fats consist of a three dimensional network structure of crystals in which liquid oil is trapped. This crystal network is held together by weak attractive forces, the nature of which is nut definitely e stablished. Crystal size is dependent on temperature history and is subject to polymorphic transitions which greatly affect the microstructure of the system. The microstructure of fats has been investigated by using polarized light microscopy, electron microscopy and X-ray diffraction analysis . Recently, a permeametric method has been developed which enables the determination of the specific surface area of the crystals in a fat. This method …

Structure And Properties Of The Particulate Constituents Of Human Milk. A Review., M. Ruegg, B. Blanc

Food Structure

Milk contains different types of colloidal or coarsely dispersed particles, such as casein micelles, membrane fragments, fat globules and cells. The fat globules are composed of subpopulations of differently sized particles. In contrast to COW 1S milk, the overall average diameter (dys), increases with advancing lactation from about 1.8 ~min colostrum to 4.0 ~min mature milk. Membrane materials originating from the milk fat globule membrane, plasma membrane, secretory vesicles and other sources can be found in milk serum. These particles have also been called lipoprotein particles. Their size ranges from about 10 - 400 nm. New results concerning the structure …

Freeze-Induced Fibre Formation In Protein Extracts From Residues Of Mechanically Separated Poultry, R. A. Lawrence, P. Jelen

Food Structure

Coagulated protein obtained by alkali extraction and acid precipitation from the bone containing residues discarded after mechanical separation of chicken was textured by freezing in semi-infinite cylinders followed by heat-setting in a microwave oven. Macrophotography was used to illustrate textural differences resulting from pH variations (4.5-6.0) in the precipitated protein, and changes in the ambient temperature used for freezing (-5°C to -32°C). Well identified, permanent fibres were fanned by the process under all conditions studied. The thickness of the fibres decreased and their radial orientation increased with increasing pH and decreasing ambient temperature of freezing. Cross-linkages between parallel fibres of …

Modeling Of Depth Distribution Of X-Ray Production, J. D. Brown

Scanning Electron Microscopy

Knowledge of X-ray production as a function of depth by electrons (𝜙(𝜚z) curves) is important in quantitative electron probe microanalysis and other electron beam technologies. Extensive measurements of such curves have been made for electron energies between 6 and 30 keV and for many X-ray lines and matrix elements. Two experimental techniques based on measurements on sandwich or wedge shaped specimens have been used.

A number of expressions have been used to model 𝜙(𝜚z) curves from a square function through complicated polynomial expressions. Recently, a Gaussian model has been proposed which accurately reflects the shape of the 𝜙(𝜚z) curves and …

Some Applications Of The Electron Backscattering Diffusion Model, W. Czarczyński, Z. Radzimski

Scanning Electron Microscopy

Starting from a simple diffusion theory extended to oblique angles of incidence some empirical correction coefficients for electron backscattering have been found. These empirical coefficients have been used in calculations of backscattered electron surface density distribution, and good agreement with experimental data has been obtained.

Inelastic And Elastic Multiple Scattering Of Fast Electrons Described By The Transport Equation, Karl E. Hoffmann, Hans Schmoranzer

Scanning Electron Microscopy

A method for solving the transport equation for the propagation of electrons in the primary energy range of interest in electron beam technology has been developed which is based on discretizing the related integral equation. The integral equation is solved by a collocation procedure yielding a system of linear equations.

The elementary scattering processes were described for elastic scattering by quantum mechanical differential cross sections and for inelastic scattering by Gryzinski type semi-empirical excitation functions for core and outer electrons separately.

From the electron flux density calculated, angular and energy distributions of transmitted and backscattered electrons were derived for various …

Reduction Of Electron Beam Induced Radiation Damage Of Organic Material By Cooling To 4 K (Cryo Electron Microscopy), I. Dietrich, E. Knapek, G. Lefranc

Scanning Electron Microscopy

Structure investigations of organic, in particular biological, material are frequently performed with a strong electron beam. If the dose is higher than le/Ų, as required e.g. for high resolution electron microscopy, the results are strongly influenced by radiation damage. There are no means for preventing breaking of chemical bonds and ionizing of atoms and fractures of molecules due to the electron impact. The secondary processes, however, such as diffusion or evaporation of the fragments, can be strongly reduced by cooling the specimen to 4 K (cryoprotection). A suitable instrument for experimenting with cryoprotection is a microscope equipped with …

Backscattering Of Electrons From Complex Structures, M. Kisza, Z. Maternia, Zbigniew Radzimski

Scanning Electron Microscopy

The backscattering of electrons from complex targets (for example, metal layer on a semi-infinite substrate with a polymer resist film above) has been studied both theoretically and experimentally. The experimental structures were exposed with an electron beam in a "spot mode". The experimental observations of developed disc radius vs. exposure time and metal layer thickness support the simple theory of scattering in such structures. The theory assumes that the backscattering causes enlarging of the exposed area by a constant value. This value is derived from the proposed scattering model based on the Archard's and Kanaya and Okayama's diffusion theories. The …

Electron Scattering And Energy Losses As A Function Of The Incident Energy: Application To Chemical Analysis, Bernard Jouffrey

Scanning Electron Microscopy

This paper gives a rapid overview on the use of the energy losses suffered by an incident electron beam. General approximations are remembered. Then some recent results on inner shell excitations as a function of energy (in high voltage electron microscopy) are given, and the problem of thick samples is rapidly discussed.

The problem of the observation of sensitive materials in electron microscopy is discussed. A simple model is proposed to determine some orders of magnitude on the inelastic mean free path and the elementary volume of defects created during the irradiation with electrons of different energies. This model can …

Electron Energy Loss Microspectroscopy And The Characterization Of Solids, Richard Leapman

Scanning Electron Microscopy

The inelastic scattering of fast electrons provides a detailed means of characterizing the chemical composition and electronic properties of thin samples in an electron microscope. Collective and single-electron excitations occuring in the low energy region of the spectrum can be described in terms of the generalized dielectric formulation. Important information is contained in this part of the spectrum but some prior detailed knowledge of the sample is usually required for proper interpretation. The core excitations allow microanalytical information to be obtained and quantitative procedures are now quite well developed at least for K and L edges. Sample thickness is one …

Analytical Scanning Electron Microscopy For Surface Science, Olive Lee-Deacon, Claude Le Gressus, Daniel Massignon

Scanning Electron Microscopy

To correlate an electron image with surface properties requires thorough understanding of electron-solid interaction, secondary electron emission mechanism and operation functions of image detectors. We emphasize the importance and usefulness of combining electron spectroscopy with scanning electron microscope in interpreting electron image contrast. Linear relationships among secondary electron image (SEI) brightness, total emission current and the integration of electron energy distribution were measured. We propose that channeling effect, instead of primary electron diffraction, is the crystallographic cause of SEI contrast. Secondary electrons contribute most to SEI brightness because of their high constituent in total yield, not because of high efficiency …

Monte Carlo Calculations For Electron Microscopy, Microanalysis, And Microlithography, David F. Kyser

Scanning Electron Microscopy

The methodology of Monte Carlo simulation for electron scattering and energy dissipation in solid targets is reviewed. The basic concepts of single and multiple elastic scattering models are compared, and the continuous energy loss model for inelastic scattering is discussed. Some new developments in Monte Carlo simulation are reviewed, including improvements in the elastic scattering model and discrete models for inelastic scattering. A variety of practical applications of Monte Carlo calculations in the fields of electron microscopy, electron probe microanalysis, and electron beam lithography are reviewed. The Monte Carlo computer program listings available in the literature are also described.

Analytical Models In Electron Backscattering, Heinz Niedrig

Scanning Electron Microscopy

The different aspects of electron backscattering from solid films are calculated in terms of simple analytical models for thin films and bulk targets, for normal and oblique incidence. Well-known models regard only one scattering aspect, e.g.: single Rutherford scattering by Everhart's model, diffusion from a point source by Archard's model, diffusion from sources continuously distributed over the depth of the target by Thümmel's model. A few analytical models have been developed recently regarding single scattering and continuous diffusion, e.g. by Werner and by the author. These models allow us to calculate analytically the backscattering coefficient for bulk targets versus atomic …

Elastic Scattering Of Electrons By Atoms, P. Rez

Scanning Electron Microscopy

Elastic scattering is defined as scattering in which the incident particle or radiation does not give up any of its energy to the scatterer. Electrons are elastically scattered in atoms by both the nucleus and the atomic electrons which screen the nuclear charge. When considering only nuclear scattering the first Born approximation quantum mechanical cross section and the classical Rutherford cross section are identical. The effects of the atomic electrons can be taken into account by a simple screening term or by more exact treatments based on Hartree-Fock or Dirac-Fack wave functions. The partial wave expansion can be used to …

Electron Signal And Detector Strategy, L. Reimer

Scanning Electron Microscopy

The scintillator-photomultiplier combination (Everhart-Thornley detector) for detecting secondary and backscattered electrons (SE and BSE) has the best properties concerning signal-to-noise ratio and bandwidth as compared to other detectors (semiconductor detectors or channel plates).

Two opposite Everhart-Thornley detectors A and B are proposed for a better and reproducible angular selection of the SE. The field strength at the specimen is reduced either by a grid or ring electrode to separate the SE with regard to their exit momenta. This offers the possibility to record the signals A, B, A+B, and A-B. The signal A+B shows material and channelling contrast and the …

Generation, Collection And Properties Of An Se-I Enriched Signal Suitable For High Resolution Sem On Bulk Specimens, Klaus-Ruediger Peters

Scanning Electron Microscopy

At useful magnifications of 100,000 to 200,000 times, high topographic resolution becomes possible on bulk specimens with a secondary electron (SE) signal, generated by the probe at the site of incidence (SE-I signal), if SE, generated in the microscope chamber or the column by BSE or by electrons of the probe, are suppressed. SSE-dependent SE make up to 90% of the collected SE signal and add to the SE-I signal a high noise component that deteriorates topographic SE-I contrasts. SE-Ill, produced by BSE at the lower pole piece of the microscope, account for 60-70% of the SE signal. SE-Ill generation …

Backscattered Electron (Bse) Imaging In The Scanning Electron Microscope (Sem) - Measurement Of Surface Layer Mass-Thickness, Oliver C. Wells, Richard J. Savoy, Phillip J. Bailey

Scanning Electron Microscopy

Sometimes, the sample to be examined in the SEM will consist of a compositionally non-uniform substrate that is covered by an approximately uniform surface layer. With a low enough incident beam energy, only the surface layer can be seen in the SEM image. The underlying structure can be seen in the secondary electron (SE) image if the range of the incident electrons is greater than twice the thickness of the surface film. In the backscattered electron (BSE) image the threshold energy is higher because the BSE detector is insensitive to slow electrons. The information depth in the BSE image was …

Correlation Of Microscopic Structure Of Corn Starch Granules With Rheological Properties Of Cooked Pastes, D. D. Christianson, F.L. Baker, A.R. Loffredo, E. B. Bagley

Food Structure

The progressive geometric changes that occur in swelling of corn starch granules during heating throughout the range of gelatinization (63-72°C) and at higher temperatures when substantial amount s of soluble starch are released from the granule were observed by scanning electron microscopy (SEM). Corn starch granules begin to swell radially, then undergo radial contraction and random tangential expansion. They form complex geometrical structures at the midpoint range (67-70°C) unlike the more uniform single-dimensional tangential swelling that occurs with lenticular granules of wheat starch . At higher temperatures, when starch begins to solubilize, corn starch granules lose their distinct ridges and …

Protein Bodies In Dormant, Imbibed And Germinated Sunflower Cotyledons, R. D. Allen, H. J. Arnott

Food Structure

Scanning electron microscopy was used to observe the morphology and structure of protein bodies in dormant and imbibed sunflower cotyledons and to document the morphological changes in protein bodies during germination and seedling growth. In order to clearly visualize dormant seed structure, anhydrous fixation techniques were employed. Definite differences in cellular structure are seen in comparisons of dry and imbibed seed tissues. As germination proceeds, protein bodies lose their smooth spherical shape and become indented and pitted. Protein body coalescence and fusion precedes the formation of a central protein vacuole. As protein is hydrolyzed, protein vacuole density decreases, and its …

Effect Of High Hydrostatic Pressure On Meat Microstructure, E. A. Elgasim, W. H. Kennick

Food Structure

Bovine longissimus muscle was prerigor pressure treated at 103.5 MNm- 2 at 37 °C for 2 min and immediately sampled, fixed and examined by light microscopy, scanning and transmission electron microscopy. Parameters like pH, Warner-Bratzler shear force values and sarcomere length were measured and related to the microscopic observations. Pressure treated samples have shorter sarcomere length, lower pH and W-B values. Physical changes include separation of sarcolemmal and endomysial sheath, contraction bands, disruption of myofibrillar structure and increased interfibrillar and intermyofibrillar spaces. At the subcellular levels, disappearance of glycogen granules, appearance of swollen mitochondria, sarcoplasmic reticulum and in some cases …

Instrumental And Sensory Analysis Of The Action Of Catheptic Enzymes On Flaked And Formed Beef, S. H. Cohen, R. A. Seagars, A. Cardello, J. Smith, F. M. Robbins

Food Structure

Texture profile analysis, Instron punch and die testing, laser diffraction measurements and scanning electron microscopy (SEM) were used to evaluate the effects of catheptic enzymes on flaked and formed beef. Although salt (NaCl) and sodium tripolyphosphate (TPP) have often been used to improve the textural quality of flaked and formed beef, the catheptic enzymes used in this study were shown to be as effective as NaCl/TPP, and in many cases more effective, in improving the textural characteristics of this product. Instron punch and die and scanning electron photomicrographic analysis showed that the enzyme and NaCl/TPP samples were quite similar; however, …

Grain Structure And End-Use Properties, Y. Pomeranz

Food Structure

Practical implications of grain structure relate to every step from grain development and production through market ing to processing, utilization, and consumption . The structure and adherence of the hulls may contribute to protection of grain during germination or malting and protection against insect infestations . Germ retention during threshing and separation during processing depend on the germ structure and location in the kernel. The subaleurone and central endosperm layers differ in cell size, shape, and structure and in composition, especially with regard to protein contents and quality. The main factors in grain hardness are the intrinsic hardness of the …

Scanning Electron Microscopy Of The Pericarp And Testa Of Several Sorghum Varieties, C. F. Earp, L. W. Rooney

Food Structure

Pericarp thickness (determined by Z gene) varies greatly among sorghum varieties ranging· from very thin (8 ~ m) to very thick (160 ~m ) . Pericarp thickness also varies within an individuual kernel. The areas below the style and near the hilum are the thickest with the sides of the kernel being thinnest . Scanning electron microscopy was used to document differences in pericarp thickness and to explain milling differences . Varieties with a thick pericarp had starch granules in the mesocarp cell layers. Sorghums with a thin pericarp did not have starch granules in the mesocarp except near the …

Freeze-Etch Of Emulsified Cake Batters During Baking, J. D. Cloke, J. Gordon, E. A. Davis

Food Structure

Cryofixation, freeze-etch techniques were used to study the structure of cake batters made from a lean cake formulation before heating and after heating to temperatures up to l00-l02°C. Batters were prepared without added emulsifiers and with saturated and unsaturated monoglycerides replacing 5 and l 0% of the oil. Unsaturated monoglyceri des were more effective than saturated monoglycerides in dispersing oil droplets through the batter. Saturated monoglycerides formed liquid crystals during baking. The temperature at which starch granules began to swell was slightly higher for saturated monoglyceride containing cakes. The batter matrix between starch granules was more clearly defined in unsaturated …

Morphological And Textural Comparisons Of Soybean Mozzarella Cheese Analogs Prepared With Different Hydrocolloids, C. S. Yang, M. V. Taranto

Food Structure

The morphology and texture of mozzarella cheese analogs prepared from soy protein isolate, gelatin, fat and different hydrocolloids (gums) were evaluated and compared. The fracturability, hardness and adhesiveness of the cheese analog gels were found to be proportionally related to the amount of fat and gelatin, and concentration and viscosity of gums. However, the stretchability of the cheese analog progels was not controlled by the viscosity of gums, but by the amount of gum and gelatin in the formulation. Fat content affected the fracturability and hardness, but did not have a significant effect on the other textural parameters or stretchability. …

Cross Sections For Inelastic Scattering Of Electrons By Atoms - Selected Topics Related To Electron Microscopy, Mitio Inokuti, Steven T. Manson

Scanning Electron Microscopy

We begin with a resume of the Bethe theory, which provides a general framework for discussing the inelastic scattering of fast electrons and leads to powerful criteria for judging the reliability of cross-section data. The central notion of the theory is the generalized oscillator strength as a function of both the energy transfer and the momentum transfer, and is the only non-trivial factor in the inelastic-scattering cross section. Although the Bethe theory was initially conceived for free atoms, its basic ideas apply to solids, with suitable generalizations; in this respect, the notion of the dielectric response function is the most …

Monte Carlo Electron Trajectory Calculations Of Electron Interactions In Samples With Special Geometries, Dale E. Newbury, Robert L. Myklebust

Scanning Electron Microscopy

Implementing a Monte Carlo simulation for application to electron sample interactions requires use of accurate treatments of elastic and inelastic scattering. In formulating a Monte Carlo simulation, careful testing must be carried out to ensure that the calculation yields sensible and useful results. A suitable testing procedure includes calculation of (1) electron backscatter coefficients as a function of atomic number, including any necessary adjustment of scattering parameters; (2) backscatter coefficients as a function of specimen tilt; (3) backscatter and transmission coefficients for thin foils; (4) backscattered electron energy distributions; (5) electron spatial distributions; and (6) x-rays, including x-ray depth distributions, …

A Transport Equation Theory Of Electron Scattering, D. J. Fathers, P. Rez

Scanning Electron Microscopy

The use of the Boltzmann transport equation to describe electron scattering in electron microscopy and electron probe microanalysis is discussed. A method of solution is given in which the transport equation is divided into angle and energy intervals. This gives rise to a number of coupled first order differential equations. Separation into forward and backward travelling components of the electron flux distribution enables the correct boundary conditions to be imposed. Solutions are derived which take the form of matrix operators analytic in both depth and target thickness. These matrices allow derivation of other physical quantities such as X-ray or Auger …