Authors:V. T. Huang, L. Haynes, H. Levine, and L. Slade
Dielectric Spectroscopy (DS) and Thermomechanical Analysis (TMA) were used to identity the glass transition temperature (Tg) of native wheat starch, vital wheat gluten and a commercial bread, in response to changes in moisture content. An open-ended coaxial probe technique was used to measure the permittivity or dielectric constant (ɛ′) and the loss factor (ɛ″) as functions of moisture, for 2.45 GHz frequency, at constant density and temperature. Plots of ɛ′ and ɛ″ as functions of moisture content showed dramatic changes in mobility-based dielectric properties, which occur upon transition from the glassy solid to the rubbery liquid state. The modified TMA method can measure the change in viscoelastic properties aroundTg. This study further confirms that synthetic polymer science principles can be applied to food systems.
Authors:S. C. Mojumdar, C. Moresoli, L. C. Simon, and R. L. Legge
Wheat gluten (WG) proteins can be utilized to make films with novel functional properties, such as selective gas barrier properties and rubber-like mechanical properties. WG-based materials are homogeneous
A Mark III DMTA (Polymer Laboratories, Loughborough, U.K.) was used to measure the glass transition temperatures (Tg) of a commercial cracker and its dough, each equilibrated to various water activities covering a range of 0.11–0.75 for the cracker and 0.11–0.90 for the cracker dough. DMTA measures the change in the elastic modulus (E′) and loss modulus (E″), as well as that in tanδ (E″/E′), with temperature. The change in the elastic modulus with temperature for the two systems followed a pattern similar to that found for complex food polymers (gluten, amylopectin), withTg decreasing as moisture content increased. Baking did not change the location of the glass transition curve (Tgvs. moisture content); i.e. the curves for raw dough and baked finished product were somewhat superimposable, and similar to the published gluten curve, indicating that for this type of cracker containing ∼5% sugars, the protein fraction is most responsible for theTg curve.
Three types of wheat were submitted to two different milling procedures, giving rise to six flours which differed by some physico-chemical characteristics such as particle size, level of damaged starch and protein content. Differential scanning calorimetry was used for monitoring heat-induced structural changes in flour aqueous dispersions 80% water and in doughs 45% water. Differences between the thermal behaviour of the flour dispersions and doughs were explained mainly by differences in protein content. This result was confirmed after partial substitution of flour by gluten. Dynamic mechanical analysis performed at 20°C on the flour doughs indicated, as expected, a linear increase in the elastic modulus with increasing protein content. The results did not bring any evidence that, under these experimental conditions, starch damage might affect gluten hydration.
Authors:Garry Kerch, Alexander Glonin, Janis Zicans, and Remo Merijs Meri
-disulfide interchange reaction is used to explain the action of ascorbic acid. The network of disulfide bonds formed in the gluten structure plays a significant role in retaining the carbon dioxide produced during fermentation and results in higher volume and improved
Thermomechanical properties of bread components can be used to characterize various events that have direct rheological impacts. The objective is to observe changes that occur during staling and toughening of a bread or similar products. In this article, characterization of bread polymers, starch and gluten, were examined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA).
Authors:R. Briones-Martínez, M. Juárez-Juárez, M. Oliver-Salvador, and M. Cortés-Vázquez
DSC was used to study the extent of denaturation of hemisphaericin and mexicain hydrolysates from corn gluten, soybean and
sunflower meals. It was observed that the defatted meals studied exhibited only one broad peak transition. The data obtained
demonstrated that the partial protein denaturation found with hemisphaericin or mexicain is correlated to modifications of
functional properties. The two enzymes display different modes of action, according to the protein source.
Authors:A. Nicolás, A. Trifone, L. Delgado, and S. Nassiff
Proline and hydroxyproline are two amino acids which due to their analogous chemical structures give similar reactions and often appear together. In view of the high percentage of proline in wheat gluten we have investigated the presence of hydroxyproline in wheat flour. We have developed a method to separate the two amino acids after separation from other interfering amino acids which are present in flour. The method of separation utilizes an ion-exchange column/Dowex 50 X-8, 100–200 resin/. The separated amino acids are determined either by spectrophotometry or isotope dilution /14C/ The latter method is more rapid and more sensitive than the spectrophotometric method.
Authors:D. Fessas, M. Signorelli, Ambrogina Pagani, Manuela Mariotti, Stefania Iametti, and A. Schiraldi
Thermal analysis was used to check the role of the main components of buckwheat flour (polysaccharides and proteins) to assess
guidelines for novel recipes for bread from wheat and buckwheat flour blends with improved nutritional properties.
The structure-related poor protein quality, namely, the lack of network-forming links, severely limits the use of buckwheat
flours in bread-making.
Data from TG and DSC analysis indicate that the introduction of a de-hulling step in the buckwheat milling diagram and the
addition of some buckwheat polysaccharide fractions, isolated from the buckwheat husk, that contribute to the formation of
the crumb structure thanks to their effect on the phase separation driven by the thermodynamic incompatibility with wheat
gluten proteins, allows one to tune opposite effects and obtain bread from de-hulled buckweat/wheat flour blends with alveolar
distribution much close that of the wheat bread.