Cereal Proteins

Cereal proteins play a key role in determining the quality of breads, biscuits, and other processed cereal-based foods. This is particularly true of cereal storage proteins, the prolamins, which in some cereals can account for half the total protein. Understanding prolamin structure-function relationships is therefore an important scientific and technical challenge. Amino acid sequencing has shown that all cereal prolamins, with the exception of the major zeins, belong to a single protein...

Gelatinization and Pasting

Rapid Visco Analyer

Gelatinization of starch is responsible for its change properties during the preparation and processing of food. After a survey conducted among starch scientists and technologists (Atwell et al. 1988), the following definition was proposed for gelatinization Starch gelatinization is the collapse (disruption) of the starch granule manifested in irreversible changes in properties such as granular swelling, native crystallite melting, loss of birefringence, and starch solubilization. The point of...

Effect Of Variables

Many studies of extrudates have altered protein sugar, salt, and fat levels, usually relative to a starch control. Expansion or solubility properties are usually measured mechanical or textural properties are less commonly assessed. A. Effect of Water Content or Relative Humidity Here, process water content can be very different from actual sample water content. In the studies of Faubion and Hoseney (29) using the Warner-Bratzler method, the shear strength fell by a factor of 3 for starch and...

References

Encyclopedia of NMR. New York Wiley, 1996. 2. M.J. McCarthy. Magnetic Resonance Imaging in Foods. New York Chapman and Hall, 1994. 3. B.P. Hills. Magnetic Resonance Imaging in Food Science. New York Wiley, 1998. 4. L. Meulenkamp, F. Vergeldt, P.A. de Jager, D. van Dusschoten, and H. van As. Quantitative NMR microscopy, chlorophyl fluorescence and water uptake rate measurements to study water-stress tolerance in plants. Conference abstract Towards whole plant...

Starch

Amylopectin Branch

The structure and functionality of starch has been the subject of intensive study and has been extensively reviewed (21). Figure 1 shows what might be called the ''standard'' model of a native starch granule, which has been formulated to fit small-angle and wide-angle X-ray scattering data. The granule is too small to permit direct imaging of its internal structure with an NMR microscope, but NMR relaxometry and diffusometry can provide unique insights into the dynamic state of water within the...

The Starch Granule

Rice Starch Granules Sem

The basic physical structural unit of starch is the granule, which has a distinctive microscopic appearance for each botanical source. The common starches are readily identifiable by using a polarizing light microscope to determine their size, shape, and form and the position of the hilum botanical center of the granule . Jane et al. 1994 have demonstrated that starch granules from different biological sources roots and tubers, grains, maize, peas and beans, fruits, and nuts could present a...

Rheological Comparison Between Synthetic And Food Polymers

Polymer Glass Transition

It was not until the early 1980s that food scientists, led by Drs. Harry Levine and Louise Slade, realized that synthetic polymer principles are applicable to food systems 1-8 . Various thermal analysis techniques have demonstrated the similarity between them 9-11 . Figure 1 shows the five regions of viscoelasticity of a synthetic polystyrene AB glassy region, BC glass transition region, CD Figure 1 Five regions of viscoelasticity, illustrated by using a polystyrene sample. Also shown are the...

Melting and Gelatinization of Starches

Step And Piecewise Functions Worksheets

Melting and gelatinization are phase transitions that are associated with the transformation of the crystalline regions of partially crystalline starch to amorphous liquid. These endothermic transitions can be detected and monitored using DSC. It is well established that the thermal stability of the crystalline phase in starch decreases by increasing the amount of water present in the system. Furthermore, while, at low lt 20 and high gt 65 moisture contents only one endothermic transition is...

Mass Transfer Models

According to the polymer literature, mass transfer can be classified according to the governing mechanisms into three basic categories zero order, case I, and case II 51 . Zero-order transport, termed constant-rate drying, refers to the case where the moisture content varies linearly with time, such as during the initial stages of drying, when the rate of moisture removal at the surface is equal to the rate of moisture transport to the surface. Zero-order transport is generally observed only...

Info

The mechanical properties of wheatflake components. Carbohydr Polym 24 305-311, 1995. DMR Georget and AC Smith. The mechanical properties of processed cereals. J Therm Analy 47 1377-1389, 1996. DMR Georget and AC Smith. A study of the effect of water content on the mechanical texture of breakfast wheat flakes. In. GR Fenwick, C Hedley, RL Richards, and S Khokhar, eds. Agri-Food Quality. London Royal Society of Chemistry, 1996, pp 196-199. DMR Georget, PA Gunning, ML...

Farinogram Weakness

Alveogram Values

Shear and elongation deformations beyond the rupture limits Elongation deformations below the rupture limits Permeability, diffusivity Gas-cell formation, disproportionation, and coalescence Elongation deformations below the rupture limits Permeability, diffusivity Biopolymers cross-linking and phase transition Gas cell disproportionation and coalescence Water migration Source Estimations of deformation rates from Ref. 4. Source Estimations of deformation rates from Ref. 4. conditions, flow...

Crystallization of Amorphous Sugars

Amorphous Lactose Sorption

Water sorption studies of dairy powders have often shown that during storage at above 40 relative humidity RH and room temperature, large amounts of water may be sorbed initially, but during further storage the sorbed water content is reduced with storage time. For example, as early as in 1926, Supplee 5 found a gradual decrease in sorbed water content of milk powder when the material was stored at 50 RH at room temperature. Such decrease in sorbed water content has often been suggested to be a...

Caking And Anticaking Agents

A simple definition of caking is ''when two or more macroparticles, each capable of independent translational modes, contact and interact to form an assemblage in which the particles are incapable of independent translations.'' Caking is such a common phenomena that almost every industry dealing with powders must deal with the problems that caking can cause. For many powdered products, such as foods, detergents, pigments, fertilizers, and chemicals, one important quality criterion is whether or...

Calorimetry

Typical Dsc Transitions

Differential scanning calorimetry DSC is a thermal analysis technique that detects and monitors thermally induced conformational transitions and phase transitions as a function of temperature. A pair of matching crucibles or sample pans, one containing the sample and one serving as reference, are heated in tandem. As a crucible is heated, its temperature increases, depending on the heat capacity of the contents of the crucible. At temperatures where an endothermic transition occurs, the thermal...

Particle Size Distribution

Rosin Rammler Particle Size Distribution

The measurement of particle size and particle size distribution is one of the most widely used methods in the industry 16 , because, in combination, they affect such other physical properties of a powder system as flowability, bulk density, and compressibility 2, 17 . Even segregation will happen in a free-flowing powder mixture because of differences in particle size 18 . Because preprocessed cereal flours are rarely of uniform particle size, it is necessary to measure a great many particles...