Characterization Technique for Three Formulated Products - Essay Example

Selection of Appropriate Characterization Technique in Three (3) Different Formulated Products: Ice Cream, Cream Cheese, and Bread Dough Ice Cream: Electron Diffraction Ice cream is considered a complex food because it is more than an ice and a cream. It is made from 55-64% water, more than 28% milk and cream, about 10-14% sucrose, and with flavourings and additives for maintenance of stability of its frozen structure (Brown, 2003). Microscopically, ice cream is seen to be made of ice, air, fat and a concentrated aqueous solution (Brown, 2003). The interactions and amount of these phases determines the characteristics of the ice cream produced. Ice cream is a group of colloids that is a dispersion of different phases of small particles (Brown, 2003). Because of this, it is considered both as foam and emulsion. The air in the ice cream does not mix with the other substances but forms small bubbles in the bulk (foam). An emulsion also forms as the milk or cream is dispersed in the ice or water as well. The properties of these colloids and therefore the ice cream depend on the interface that forms between the two phases. Molecules which stick to the interfaces can stabilize the dispersion (small bubbles or fat droplets) and prevent coalescence (Goff, 2007). These molecules are called emulsifiers. In ice cream the surface of the air bubbles are covered by milk proteins (emulsifiers). The more air bubbles there are and the smaller they are, the more interface there is to be stabilized. Controlling the protein concentration and type (efficiency as an emulsifier) therefore controls the amount and size of the air bubbles. The advantage of changing the amount of air in the ice cream is that it alters the amount of ice per ‘mouthful’ and make the ice cream feel warmer (Brown, 2003). Another way of controlling the properties of ice cream is to control the amount of ice since it is approximately 60% water (Goff, 2007). An ice cream is eaten far below the freezing point of water and so it could be expected that an ice cream contains 60 ice, however, not all the water is frozen at the eating temperature (approximately -20) (Brown, 2003). Crystal size depends on how quickly the ice cream is frozen. Slow freezing gives a small number of large crystals, whereas fast freezing promotes a larger number of nucleation sites and, consequently, a large number of small crystals (Brown, 2003). Because of its structure, if the temperature increases during shipping, storage at the grocery store, or even as the ice cream is transported to a consumer's freezer, those tiny crystals can melt and re-crystallize into larger structures. Also because ice cream is a complex mix of fatty and watery components, manufacturers often have to use several different flavourings just to get ice cream with a desired taste (Goff, 2007). To curtail this problem, manufacturers add stabilizers such as plant-derived guar gum and carageenan. The stabilizers also prevent the air bubbles from collapsing and promote good flavour release. According to Goff 2007, the presence of dissolved molecules, mainly milk proteins and sugars, is the factor that affects the freezing property of a liquid. It depresses the freezing point (colligative effect). These dissolved solutes broaden the range of temperature that freezing will occur as well as when freezing begins. As a result, the amount of ice at a given temperature is sensitive to the change in solute concentration (Brown, 2003). The moles of proteins are larger than sugars, but their colligative effect is smaller (Goff, 2007). Therefore, the amount of ice in an ice cream at a given temperature can be estimated by the sugar concentration. The knowledge on the possible amount of ice present in ice cream determines its properties (Goff, 2007). One property that is largely determined by the amount of ice is how cold the ice cream feels. When you eat ice cream heat is removed from your mouth. The amount of heat removed depends on the heat energy required to raise the mouthful of ice cream from -20C to body temperature. The ice cream with higher ice content will feel colder since it removes more heat energy from the mouth. More heat energy is taken as it has more hydrogen bonds to break in order to melt all the ice. This is its latent heat. After scraped-surface freezing and hardening of ice cream, the ice crystals formed is unstable (Brown, 2003). These unstable ice crystals will undergo recrystallization wherein there are changes in number, size and shape of ice crystals during frozen storage. The constancy of ice crystals depends on the equilibrium freezing curve (Goff, 2007). It involves small crystals disappearing, large crystals growing, and crystals fusing together. There are several types of recrystallization processes (Brown, 2003). Iso-mass recrystallization involves changes in surface or internal structure for irregular crystals and large surface-to-volume ratios assume a more compact structure. Therefore, flatter surfaces are more stable than sharp ones. Migratory recrystallization is for larger crystals possibility to grow at the expense of smaller crystals. Ostwald ripening is the migratory recrystallization. This occurs at constant temperature and pressure as a result of differences in surface energy between crystals, most likely involving melting-diffusion-refreezing or sublimation-diffusion-condensation mechanisms. This is increased by temperature fluctuations (heat shock) inducing a melt-refreeze behavior due to ice content fluctuations. Electron diffraction is applied to study matter and is accomplished firing to a sample and observe the resultant interference pattern (Krumeich, 2006). It occurs due to the wave-particle duality, thus, an electron can be regarded as a wave much like sound or water waves. Therefore, it appears to be similar to X-ray diffraction and neutron diffraction. It has been used under solid state physics and chemistry to study the crystal structure of solids (Krumeich, 2006). Thus, this could be tried in the characterization of ice cream. These experiments are usually performed in a transmission electron microscope (TEM), or a scanning electron microscope (SEM) as electron backscatter diffraction where electrons are accelerated by an electrostatic potential to obtain the desired energy and wavelength before sample interaction. The crystalline solid acts as a “diffraction grating, scattering the electrons in a predictable manner” (Krumeich, 2006). It is then possible to interpret the structure of the crystal producing the diffraction pattern (Brown, 2003). But this technique has it limitation that includes phase problem. This is also a useful technique for evaluation of short range order of amorphous solids, and the geometry of gaseous molecules. According to the study of Bendersky and Gayle 2001, electrons in diffraction are charged particles and interact with matter through the Coulomb forces being influenced to both the positively charged atomic nuclei and the surrounding electrons. In addition, there is non-zero magnetic moment of neutrons, thus, scattered in magnetic fields. Furthermore, the electron lenses allow the geometry of the diffraction experiment to be varied (Bendersky and Gayle, 2001). The parallel beam of electrons incident on the specimen is the simplest conceptual geometry formed. But “by converging the electrons in a cone onto the specimen, one can in effect perform a diffraction experiment over several incident angles simultaneously” (Bendersky and Gayle, 2001). This technique is called Convergent Beam Electron Diffraction (CBED) revealing full three dimensional symmetry of the crystal. The electrons scatter through the sample as they pass through the electromagnetic lens. This lens acts to collect all electrons scattered from one point of the sample in one point on the fluorescent screen, causing an image of the sample to be formed. The electrons are scattered in the same direction by the sample and are collected into a single point where the diffraction pattern is formed (Bendersky and Gayle, 2001). By manipulating the magnetic lenses of the microscope, the diffraction pattern may observed by projecting it onto the screen instead of the image. Electron diffraction in TEM is subject to several important limitations (Bendersky and Gayle, 2001). The sample must be electron transparent (100 nm or less), thus, the sample preparation is time-consuming. While on the other hand, some samples are vulnerable to radiation damage of the incident electrons. However, the main limitation of electron diffraction in TEM remains the comparatively high level of user interaction needed (Bendersky and Gayle, 2001). Another disadvanatage is it requires a much higher level of user input. An SEM may typically operate at 10,000 volts (10 kV) giving an electron velocity approximately 20% of the speed of light, while a typical TEM can operate at 200 kV raising the electron velocity to 70% the speed of light (Krumeich, 2006). We therefore need to take relativistic effects into account. The wavelength of the electrons in a 10 kV SEM is then 12.3 x 10 -12 m (12.3 pm) while in a 200 kV TEM the wavelength is 2.5 pm. There are other characterization techniques that have been used and studied for the examination of ice cream properties. The direct optical microscopy of ice cream was studied to develop and to set up a new optical direct microscopy method, based on the reflected light flux differences, with episcopic axial lighting to characterize the different phases structure of commercial overrun ice creams (Caillet et al., 2003). Firstly, the results obtained have been validated by two others methods, a destructive method by dispersion and observation by light microscopy and, an indirect method, by scanning electron microscopy after freeze-drying sample. It was observed that the three methods were in agreement and led to the same conclusions concerning the main freezing parameters influence. So, this technique has been principally used to investigate the effects of the freezing conditions on the ice crystal structure. One of the most important parameters is the freezing rate that governs not only the size, but also the rate of crystallization. Another technique considered is the Micro-Slicer Image Processing System (MSIPS) (Ueno et al., 2004). It has been applied to observe the ice crystal structures formed in frozen dilute solutions. Several characteristic parameters were also proposed to investigate the three-dimensional (3-D) morphology and distribution of ice crystals, based on their reconstructed images obtained by multi-slicing a frozen sample with the thickness of 5 μm. The values of characteristic parameters were determined for the sample images with the dimension of 530×700×1000 μm. The 3-D morphology of ice crystals was found to be a bundle of continuous or dendrite columns at any freezing condition (Ueno et al., 2004). The equivalent diameter of ice crystals were in the range of 73–169 μm, and decreased exponentially with increasing freezing rate at the copper cooling plate temperature of −20 to −80 °C. At the Tcp −40 °C, the volumes of ice crystals were in the range of 4.6×104 μm3 to 3.3×107 μm3, and 36 ice columns were counted in the 3-D image The examination of microstructure of ice cream will contribute much to earlier prevention of defects in flavour, body and texture, melting quality, colour, and shrinkage (Goff, 2007). The flavour defects can be classified according to the flavouring system (lacks flavour or too high flavour, unnatural flavour), the sweetening system (lacks sweetness or too sweet), processing related flavour defects (cooked), dairy ingredient flavour defects (acid, salty, old ingredient, oxidized/metallic, rancid, or whey flavours), and others (storage/absorbed, stabilizer/emulsifier, foreign). The unnatural flavour is caused by using flavours that are not typical of the designated flavour and too much egg in an ice cream that is not specified as a custard ice cream (Goff, 2007). Another flavour defect is due to heating too much or using excessively high temperatures in mix pasteurization when using milk products (Goff, 2007) but it will eventually dissipate with time, the same as cooked defect in fluid milk. According to Goff 2007, the use of dairy products with high acidity (usually due to bacterial spoilage) or holding mix too long and at too high a temperature before freezing produces highly acidic ice cream. But nowadays, the acid or sour flavours are more rare due to the growth of proteolytic psychrotrophs during storage at elevated temperatures rather than lactic acid bacteria. Salty ice cream has too high milk solids-not-fat content (Goff, 2007). Too much salt may have been added to the mix. These include whey powder, maybe salted butter, and whey flavour graham cracker like. Another cause of flavour defect is the use of inferior dairy products in the preparation of the mix (Goff, 2007). Powders made from poor milk or butter made from poor cream will contribute to old ingredient flavour. Poor egg can also cause unpleasant after taste (Goff, 2007). Another factor is the oxidation of the fat or lipid material such as phospholipid, similar to fluid milk oxidation (Goff, 2007). This is induced by the presence of copper or iron in the mix. The Mono- and diglycerides or Polysorbate 80 can also oxidize. Another observable fact is the rancidity of certain fats (Goff, 2007). This may be due to use of rancid dairy products or to insufficient heat before homogenization of mix. Egg yolk powder may also be the cause. Another incident is lipolysis especially the release of free butyric acid (Goff, 2007). Other contributing factor to flavour defect is improper storage (Goff, 2007). It is most pronounced on ice cream which had been held in a stale storage atmosphere. Ice cream can also pick up absorbed volatile flavours from the storage environment (e.g., paint, ammonia, or in dipping cabinets - volatiles from nearby flavours). Another characteristic to be determined and studied is the ice cream’s body and texture (Goff, 2007). The Coarse or Icy Texture is due to the presence of ice crystals of such a size that they are noticeable when the ice cream is eaten (Goff, 2007). This may be caused by insufficient total solids, insufficient protein, insufficient stabilizer or poor stabilizer, insufficient homogenizing pressure (due to its effect on fat structure formation), and insufficient aging of the mix (stabilizer hydration, also fat crystallization and development of resulting fat structure). It is also caused by slow freezing because of mechanical condition of freezer, incorporation of air as large cells because of physical characteristics of mix or type of freezer used, slow hardening, fluctuating hardening room temperatures, rehardening soft ice cream, pumping ice cream too far from continuous freezer, and fluctuating temperatures during storage and distribution which is the most likely cause. Another defect is the Crumbly Body (Goff, 2007). The flaky or snowy characteristic is caused by high overrun. low stabilizer or emulsifier, low total solids, and coarse air cells. The Fluffy Texture or spongy characteristic is caused by incorporation of large amount of air as large air cells, low total solids, and low stabilizer content (Goff, 2007). The Sandy Texture is one of the most objectionable texture defects but easiest to detect (Goff, 2007). It is caused by Lactose crystals which do not dissolve readily and produce a rough or gritty sensation in the mouth. This can be distinguished from "iciness" because the lactose crystals do not melt in your mouth. This defect can be prevented by many of the same factors that inhibit iciness. These factors are hardening the ice cream quickly, maintaining low hardening room temperatures, and preventing temperature fluctuations from manufacturer to consumer. The Gummy Body is the opposite of Crumbly in that it imparts a pasty or putty-like body (Goff, 2007). It is caused by too low overrun, too much stabilizer, and poor stabilizer. The Weak Body lacks "chewiness" and melts quickly into a watery liquid. It gives an impression of lacking richness. It may be caused by low total solids, high overrun, and insufficient stabilizer. On the melting defects, the Curdy Melt-Down may be due to visible fat particles or due to coagulation of the milk proteins, thus, is affected by factors that influence fat destabilization or the protein stability such as high acidity (protein coagulation), salt balance (protein coagulation), high homogenizing pressures (fat coagulation), and over-freezing in the freezer (fat coagulation) (Goff, 2007). If it does not melt, this may be caused by over emulsification, wrong emulsifier, high fat, excessive fat clumping in the mix due to homogenization at too low a temperature or single-stage homogenizer, and freezing to too low a temperature at freezer (Goff, 2007). Goff 2007 also added that Wheying off is due to the salt balance, protein composition, and carrageenan addition (or lack or it). In colour defects, if the colour is uneven, it applies usually to ice cream in which colour has been used, but may be noticed in vanilla ice cream under some circumstances (Goff, 2007). If it is unnatural, a wrong shade of color may had been used for flavoured ice cream, too much yellow coloring was used in vanilla ice cream, and grayish color was due to neutralization (Goff, 2007). The shrinkage is a very troublesome defect in ice cream since there appears to be no single cause or remedy (Goff, 2007). Defect shows up in hardened ice cream and manifests itself in reduced volume of ice cream in the container usually by pulling away from the top and/or sides of container. Structurally, it is caused by a loss of spherical air bubbles and formation of continuous air channels. Some factors believed associated with the defect are freezing and hardening at ultra low temperatures, storage temperature (both low and high appear to contribute), excessive overruns, pressure changes (e.g. from altitude changes: lids popping when shipped to high altitudes, shrinkage when returned to low altitudes). References Bendersky, L.A. and Gayle F.W. ‘Electron diffraction using transmission electron microscopy’, Journal of Research of the National Institute of Standards and Technology, 106: 997–1012, , 2001 (accessed 22 January 2007). Brown, P. ‘The properties of ice cream’, University of Bristol, School of Chemistry, , 2003 (accessed 22 January 2007). Caillet, A., Cogne, C., Andrieu, J., Laurent, P., Rivoire, A. ‘Characterization of ice cream structure by direct optical microscopy. Influence of freezing parameters’, Centre National de la Recherche Scientifique (CNRS), 36: 743-749, , 2003 (accessed 22 January 2007). Goff, H.D. ‘Ice cream’, Dairy Science and Technology Education Series, University of Guelph, , 2007 (accessed 22 January 2007). Krumeich, F. ‘Electron diffraction (ED)’, Swiss Federal Institute of Technology Zurich, , 2006 (accessed 22 January 2007). Ueno, S., Do, G., Sagara, Y., Kudoh, K., and Higuchi, T. ‘Three-dimensional measurement of ice crystals in frozen dilute solution’, International Journal of Refrigeration, 27 (3): 302-308, , 2004 (accessed 22 January 2007). Cream Cheese: X-ray Microtomography Fresh cheeses are highly perishable, and cream cheese is no exception. Cream cheese is categorized as a fresh cheese since it is unaged (Filippone, n.d.). It should always be kept refrigerated. This is one cheese that you do not want aged. Cream cheese is the widely consumed cheese by Americans. Its soft, rich, and creamy texture made it also to the international market and became part of many recipes either as an ingredient or as a spread. It is made from cream or from a mixture of cream and milk or skim milk (Sainani et al., 2004). Traditionally, this cheese mix is pasteurized, homogenized, inoculated with lactic culture, and held at 23°C until it attains a pH of approximately 4.6. The curd is heated from 52°C to 63°C, and stabilizers, emulsifiers and salt are added (Filippone, n.d.). This mixture is homogenized and is packed either cold or hot. The United States Department of Agriculture had set standard specifications in the production of cream cheese (USDA, 1994). Its moisture content must not be more than 55%, milkfat must not be less than 33% total fat (marketed), pH range must be 4.4 to 4.9, and salt content must not be more than 1.4%. It shall possess slight lactic acid and cultured diacetyl flavor and aroma. It must not have off flavors or odors like bitter, flat, sulfide, or yeasty. As a homogenized mixture with soft, smooth, creamy, and rich consistencies, these qualities can be further characterized, examined, and proved under x-ray microtomography (XMT). Since XMT can probe microstructures non-invasively up to a few millimeters across and to a few micrometers at axial and lateral resolution, this can be tried to cream cheese for quality assurance through texture. In cream cheese, this texture determines the acceptance of cream cheese to consumers based on its sensory effect that made it distinct from other cheeses. X-ray microtomography (XMT) has been commonly used in medical applications like medical and pharmaceutical research, and dentistry. Its use already expanded to biological sciences like botany and zoology, and to material sciences and engineering. Recently, it was used to characterize the microstructure of bread dough (Wong and Miri, 2005). The XMT can obtain multiple x-ray “shadow” transmission images of the object from different angular views as the object rotates on a high-precision stage (Wong and Miri, 2005). The cross section images of the object are reconstructed by a modified cone-beam algorithm, creating a complete 3-D representation of internal microstructure and density over a selected range of heights in the transmission images. The best micro-CT images are obtained from objects in which microstructure coincides with contrast in x-ray absorption of the sample’s constituent materials (like water or air). The application of XMT to other foodstuffs was proved to be a very useful technique to image the 3-D microstructure of food products. XMT was considered complementary to other microscopic techniques used for food research. But like any techniques, it has its own advantages and disadvantages (Wong and Miri, 2005). The XMT is considered a non-destructive technique (coupled with image analysis). It can provide realistic 3-D view of objects on a cross-section and is done non-invasively. It has the possibilities to rotate and cut the object model. It also has a high spatial resolution of 1x10-7 mm3. It has in-house software or any commercial modelling packages that can be linked up to do further analyses e.g. 3-D size distributions. The XMT allows visualization and image analysis of the full 3-D microstructure, measuring the size, shape, networking or connectivity and distribution of various phases (Gregory et al., 2003). These measurements will represent the full 3-D microstructure, which is not always possible by 2-D image analysis using statistical techniques. This is in particular the case for channelling and network phenomena. Combined visualization of the microstructure using XMT and other microscopic techniques, extraction of quantitative data obtained by image analysis, and modelling of the microstructure based on characteristics of the structuring elements should point to the optimal food product. The function of XMT is limited because it has no temperature control, does not like wet samples, and measurements are still relatively subjective (scanning and raw data, 2-D reconstruction, 3-D rendering) (Wong and Miri, 2005). Validations of algorithms for measurement of porosity are also needed (Wong and Miri, 2005). Sainani et al. (2004) studied the microstructure of three different cream cheese preparations (induced grittiness, commercially smooth, and gritty) under electron microscope, both transmission and scanning. Under these techniques, they were able to identify significant differences that will determine the quality grade of the cream cheese. The study aims to identify the degree of grittiness in each production step and therefore determine how to minimize inducing grittiness in each step to produce a good quality cream cheese. And as standard, cream cheese produced and prepared must be smooth to achieve softness and richness which are its discrete characteristics. References Filippone, P.T. ‘Cream Cheese Recipes and Information’, Homecooking, , n.d. (accessed 21 January 2007). Gregory, P.J., Hutchison, D.J., Read, D.B., Jenneson, P.M., Gilboy, W.B., and Morton, E.J. ‘Non-invasive imaging of roots with high resolution X-ray micro-tomography’, Plant and Soil, 255 (1): 351-359, , 2003, (accessed 22 January 2007). Sainani, M.R., Vyas, H.K., and Tong, P.S. ‘Characterization of Particles in Cream Cheese’, Journal of Dairy Science, 87, , 2004 (accessed 21 January 2007). United States Department of Agriculture. ‘USDA Specifications for Cream Cheese, Cream Cheese with other Foods, and Related Products’, USDA, , 1994 (accessed 21 January 2007). Wong, D. and Miri, T. ‘X-Ray Microtomography and its Applications’, , 2005 (accessed 21 January 2007). Bread Dough: Scanning Electron Microscopy The quality of bread dough has been under increased consciousness in the baking industry especially the frozen dough. The maintenance of dough matrix and identification of the standard bread dough has been under research to establish consistency of what is a quality one. The mechanical properties of dough, such as its elasticity and viscosity, vary greatly depending on factors like the ratio of ingredients, the moisture in the air, and the room temperature (Shay, 2007). Although there's already an ample body of scientific literature devoted to dough, still many studies are conducted to reduce the degree of variability. This includes developing accurate and reproducible techniques for measuring the properties of dough, and studying its microstructure. The water and flour are the critical ingredients of bread as they affect its texture. (Schiraldi et al., 1996). Measurement by weight is much more accurate and consistent than measurement by volume, especially for the dry ingredients. The flour is 100% used in the production while other ingredients are by amount (Aibara et al., 2005). In United States, bread production involves approximately 50% water thus having finely textured, light, bread. Artisan bread formulas contain 60 to 75% water. Yeast breads have higher water percentages resulting in more CO2 bubbles, and a coarser bread crumb. It was said that one pound (500 g) of flour is enough for making a standard loaf of bread, or two French loaves (Schiraldi et al., 1996). The gas phase of bread, which makes up more than 70% of the final volume of a loaf, has a major influence on its textural and sensory attributes (Schiraldi et al., 1996). Controlling the gas phase volume is a major challenge as during proving and early stages of baking gas must be captured within bread dough, only being released at the end of baking. There is particular focus on the role that thin films lining the bubbles may play in stabilizing the foam structure of risen dough. Despite its potential importance, little is known about the surface properties or composition of the aqueous phase of doughs from which the films are thought to form and the role of surface properties in determining the aerated structure of dough, and hence the textural characteristics of bread as well as its implications for process engineering aspects of the mixing and proving stages of bread production. The electron microscope (EM) function exactly as their optical counterparts except that they use a focused beam of electrons instead of light to "image" the specimen and gain information as to its structure and composition (Yang, 2005). The basic step involved in all EM is firstly, a stream of electrons is formed and accelerated toward the specimen using a positive electrical potential. This stream is confined and focused using metal apertures and magnetic lenses into a thin, focused, monochromatic beam. This beam is focused onto the sample using a magnetic lens. These interactions occur inside the irradiated sample, affecting the electron beam. These interactions and effects are detected and transformed into an image. The scanning electron microscopy (SEM) technique is performed under scanning electron microscope that uses electrons rather than light to form an image. There are many advantages to using the SEM instead of a light microscope (electron microscopy, n.d.). The SEM has a large depth of field, which allows a large amount of the sample to be in focus at one time. The SEM also produces images of high resolution, which means that closely spaced features (like in bread dough) can be examined at a high magnification. The combination of higher magnification, larger depth of focus, greater resolution, and ease of sample observation makes the SEM one of the applicable characterization technique for bread dough matrix examination. Scanning electron microscopy (SEM) for the investigation of crystal defects has been rarely used over the years, despite several theoretical and experimental demonstrations of its utility (Pneumadu, 1996). The localized elastic distortions associated with the core region of an isolated dislocation or a small cluster of dislocations in an otherwise perfect crystal can provide enough of a perturbation in the lattice to result in a detectable variation in the backscattered electron (BSE) intensity, provided the crystal is oriented in a channeling condition (Yang, 2005). The SEM allows a good deal of analytical data to be collected in addition to the formed image (Penumadu, 1996). As the primary electrons bombard the surface of an object, they interact with the atoms of the surface to yield even more particles and radiations other than secondary electrons. Among these radiations are Auger electrons, and characteristic X-rays. The X-rays have unique, discreet energy values, characteristic of the atomic structure of the atom from which they emanated (Penumadu, 1996). If one collects these X-rays and analyzes their inherent energy, the process becomes Energy Dispersive X-ray Analysis. Combining the scan information from secondary and Auger electrons, together with the qualitative and quantitative X-ray information allows the complete molecular mapping of an object's surface. The scanning electron microscope works by bouncing electrons off of the surface and forming an image from the reflected electrons (electron microscopy, n.d.). Actually, the electrons reaching the specimen (the 1 ° electrons) are normally not used (although they can form a transmitted image, similar to standard TEM), but they incite a second group of electrons (the 2° electrons) to be given off from the very surface of the object. Thus, if a beam of primary electrons is scanned across an object in a raster pattern (similar to a television scan), the object will give off secondary electrons in the same scanned pattern. These electrons are gathered by a positively charged detector, which is scanned in synchrony with the emission beam scan. Thus, the name scanning electron microscopy is due to the image formed by the collection of secondary electrons. It is possible to focus the primary electrons in exactly the same manner as a TEM (transmission electron microscopy) (electron microscopy, n.d.). Since the primary electrons can be focused independently of the secondary electrons, two images can be produced simultaneously. Thus, an image of a sectioned material can be superimposed on an image of its surface. The instrument then becomes a STEM, or Scanning-Transmission Electron Microscope. It has the same capabilities of a TEM, with the added benefits of an SEM. Finally, the scanning microscope has one further advantage that is useful in cell structure analysis of the bread dough matrix. As the electron beam scans the surface of an object, it can be designed to etch the surface (electron microscopy, n.d.). That is, it can be made to blow apart the outermost atomic layer. As with the emission of characteristic x-rays, the particles can be collected and analyzed with each pass of the electron beam. Thus, the outer layer can be analyzed on the first scan, and subsequently lower layers analyzed with each additional scan. Electrons are relatively small, and the etching can be enhanced by bombarding the surface with ions rather than electrons (Yang, 2005). The resultant Secondary Emissions-Ion Scanning data can finally be analyzed and the three- dimensional bit-mapped atomic image of an object reconstructed. In conducting SEM, the specimen surface must be conductive or has way to conduct away excessive electrons (Yang, 2005). Due to the excessive charge built-up when examining insulator this makes imaging and analysis difficult. The SEM is foreseeable by coating a layer of conductive materials, such as carbon or gold layer, to remove the charge built-up that may introduce coating artifacts. It is also total undesirable when examining specimens like forensic evidences, precious jewelry, museum collections and thin film fabricated structures. The porous materials like brick, concrete block or bones that out-gassing will require long hour pumping to achieve the required high vacuum level. Needless to say, hydrated or wet specimens are impossible to be examined under conventional SEM. Despite all these disadvantages, conventional SEM still retains and delivers the higher imaging resolution (Yang, 2005). The fluorescence microscopy technique has been used to detect yeast cells in frozen dough (Autio and Matilla-Sandholm, 1992). It was known that yeast growth occur during storage at freezing when there is improper baking process and formulation. The yeast growth causes a sufficient damage that lead to dough matrix deterioration. The dough matrix was further damaged by the ice crystals formed during freezing. On the other hand, x-ray microtomography is used to image and identify the cell structure of freeze-dried dough (Wong and Miri, 2005). The space volume and pore size of the bread dough that determines its elasticity are evaluated. This mechanical behavior and microstructure of dough is due to its gluten (Shay, 2007). Gluten, which gives dough its elastic quality, is a type of protein compound known as a biomacromolecule, and it forms a tangled matrix that is the backbone of dough. It is near a model called critical gel (Shay, 2007). A critical gel is neither a solid nor a liquid, but something in between. The quality, shape, and distribution of gluten is known to be linked to a bread's qualities (Shay, 2007). The dough improvers, such as emulsifiers, enzymes, and dough conditioners, have been used to improve the dough properties and product quality in bread making. Thus, establishment and characterization of the dough matrix of good quality bread dough is necessary for acceptability by the consumers. References Aibara, S., Ogawa, N., and Hirose, M. ‘Microstructures of bread dough and the effects of shortening on frozen dough’, Biosciences, Biotechnology, and Biochemistry, 69 (2): 397-402, , 2005 (accessed 22 January 2007). Autio, K. and Matilla-Sandholm, T. ‘Detection of active yeast cells (Saccharomyces cerevisiae) in frozen dough sections’, Applied and Environmental Microbiology, 58 (7): 2153-2157, , 1992 (accessed 22 January 2007). Electron Micrsocopy (n.d.) (accessed 22 January 2007). Penumadu, D. ‘Evaluating clay microfabric using scanning electron microscopy and digital information processing’, Transportation Research Record, pp. 112-120, , 1996 (accessed 22 January 2007). Schiraldi, A., Piazza, L., Brenna O., and Vittadini, E. ‘Structure and properties of bread dough and crumb’, Journal of Thermal Analysis and Calorimetry, 47 (5): 1339-1360, , 1996 (accessed 22 January 2007). Shay, S. ‘Dough Nut: Could one man's work lead to better bread?’, Technology Review, , 2007 (accessed 22 January 2007). Wong, D. and Miri, T. ‘X-Ray Microtomography and its Applications’, , 2005 (accessed 21 January 2007). Yang, T.K. ‘SEM Trends and Applications’, Seminar Series, , 2005 (accessed 22 January 2007) Read More