Physical Properties and Chemical Structure of High-Amylose Corn Starch Fractions

Addition of hydrocolloids (H/C) in gluten-free (GF) bread formulation is necessary in order to act as polymeric substances that should mimic the viscoelastic properties of gluten and increase the dough’s gas-retaining ability. The properties of H/C vary depending on their origin and chemical structure. Addition of H/C (hydroxypropylmethylcellulose (HPMC), xanthan, κ-carrageenan and guar gum) of different origins at 1%, 1.5% and 2% (w/w) in GF formulations based on corn starch and rice flour was carried out to investigate the effects on dough rheology and bread quality. The consistency, viscosity and thermal properties of doughs were evaluated. According to results, 1% and 1.5% addition of H/C (except from xanthan) contributed to bread with higher loaf volume and better color compared to control GF bread as well as to increased shelf life due to its moisture-absorption ability. Sensory evaluation by a trained panel revealed a preference for bread containing 1.5% HPMC because of its loaf volume, appearance and firmness characteristics. The micrographs of the dough showed a continuous matrix between starch and HPMC obtaining a more aerated structure.

Download Full-text

Brazilian gutta-percha points. Part II: thermal properties

Brazilian Oral Research ◽

10.1590/s1806-83242007000100005 ◽

2007 ◽

Vol 21 (1) ◽

pp. 29-34 ◽

Cited By ~ 8

Author(s):

Cláudio Maniglia-Ferreira ◽

Eduardo Diogo Gurgel-Filho ◽

João Batista Araújo Silva Jr ◽

Regina Célia Monteiro de Paula ◽

Judith Pessoa Andrade Feitosa ◽

...

Keyword(s):

Differential Scanning Calorimetry ◽

Thermal Properties ◽

Physical Properties ◽

Ambient Temperature ◽

Amorphous Phase ◽

Thermal Behaviour ◽

Chemical Structure ◽

Scanning Calorimetry ◽

Gutta Percha ◽

Thermal Manipulation

This study was undertaken to explore the effect of heating on gutta-percha, analyzing the occurrence of endothermic peaks corresponding to the transformation that occurs in the crystalline structure of the polymer during thermal manipulation. This study also seeked to determine the temperature at which these peaks occur, causing a transformation from the beta- to the alpha-form, and from the alpha- to the amorphous phase. Eight nonstandardized gutta-percha points commercially available in Brazil (Konne, Tanari, Endopoint, Odous, Dentsply 0.04, Dentsply 0.06, Dentsply TP, Dentsply FM) and pure gutta-percha (control) were analysed using differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The transition temperatures were determined and analysed. With the exception of Dentsply 0.04 and Dentsply 0.06, the majority of the products showed thermal behaviour typical of beta-gutta-percha, with two endothermic peaks, exhibiting two crystalline transformations upon heating from ambient temperature to 130°. Upon cooling and reheating, few samples presented two endothermic peaks. It was concluded that heating dental gutta-percha to 130°C causes changes to its chemical structure which permanently alter its physical properties.

Download Full-text

Oxidative Aging of Natural Rubber Vulcanizates. Part III. Crosslink Scission in Monosulfidic Networks

Rubber Chemistry and Technology ◽

10.5254/1.3539269 ◽

1969 ◽

Vol 42 (3) ◽

pp. 924-935 ◽

Cited By ~ 1

Author(s):

T. Colclough ◽

J. I. Cunneen ◽

G. M. C. Hrggins

Keyword(s):

Natural Rubber ◽

Physical Properties ◽

Chemical Structure ◽

Spectroscopic Methods ◽

Chemical Probes ◽

Conjugated Diene ◽

Strain Measurements ◽

Oxidative Aging ◽

Tert Butyl Hydroperoxide ◽

Natural Rubber Vulcanizates

Abstract A natural rubber vulcanizate containing almost entirely monosulfidic crosslinks was oxidized in oxygen and with tert-butyl hydroperoxide. The changes in physical properties due to oxidation were followed by stress—strain measurements, and the changes in chemical structure were investigated with chemical probes, and by spectroscopic methods. The results show that when the oxidized vulcanizates are heated at 75° C, the monosulfidic crosslinks are broken, that crosslinks containing two sulfur atoms are formed, and that conjugated diene and triene structures are introduced into the main polyisoprene chains.

Download Full-text

Feasibility and characterization of the cycloamylose production from high amylose corn starch

Cereal Chemistry ◽

10.1002/cche.10102 ◽

2018 ◽

Vol 95 (6) ◽

pp. 838-848 ◽

Cited By ~ 2

Author(s):

Jiwoon Park ◽

Shin-Joung Rho ◽

Yong-Ro Kim

Keyword(s):

Corn Starch ◽

High Amylose

Download Full-text