Browsing by Author "Strounina, EV"

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    Effects of thermal denaturation on the solid-state structure and molecular mobility of glycinin
    (American Chemical Society, 2011-06-01) Huson, MG; Strounina, EV; Kealley, CS; Rout, MK; Church, JS; Appelqvist, IAM; Gidley, MJ; Gilbert, EP
    The effects of moisture and thermal denaturation on the solid-state structure and molecular mobility of soy glycinin powder were investigated using multiple techniques that probe over a range of length and time scales. In native glycinin, increased moisture resulted in a decrease in both the glass transition temperature and the denaturation temperature. The sensitivity of the glass transition temperature to moisture is shown to follow the Gordon-Taylor equation, while the sensitivity of the denaturation temperature to moisture is modeled using Flory's melting point depression theory. While denaturation resulted in a loss of long-range order, the principal conformational structures as detected by infrared are maintained. The temperature range over which the glass to rubber transition occurred was extended on the high temperature side, leading to an increase in the midpoint glass transition temperature and suggesting that the amorphous regions of the newly disordered protein are less mobile. C-13 NMR results supported this hypothesis. © 2011, American Chemical Society
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    Hydration study of soy protein in the ‘dry state’
    (Royal Society of Chemistry, 2008-05-19) Kealley, CS; Rout, MK; Appelqvist, IAM; Strounina, EV; Whittaker, AK; Gidley, MJ; Gilbert, EP; Lillford, PJ
    The work reported focuses on the methodology employed by the Australian Food Futures collaboration to the study of proteins in the dry state. To date, 'dry' proteins (here used to describe solids with a moisture content <30% w/w) have been characterised by differential scanning calorimetry (DSC), fourier transform - infrared spectroscopy (FT-IR), 1H t2 relaxation and 13C high resolution nuclear magnetic resonance (NMR) spectroscopy and small angle x-ray scattering (SAXS). The case study presented in this paper centres on the use of these techniques to characterise the differences in structure between native and denatured glycinin, a soy protein, at low and controlled moisture contents. The glass transition temperature of native soy glycinin (11S) at room temperature (∼ 27°C), is at a moisture content of 13.4%, whereas the denatured soy glycinin undergoes a glass transition at 46°C at the same moisture content. With increasing water content, NMR experiments show that proton exchange with protein surfaces (*H T2) and protein segmental mobility (13C) both increase. A β - sheet toβ - turn structural rearrangement is inferred as the position of the Amide-I FT-IR band shifts from 1634 to 1630 cm"1. Proton T2 relaxation rates range from < 1 ms to 25 ms, with shorter (< 1 ms) relaxation rates dominant up to 17.4% moisture for both native and denatured glycinin. ,13C NMR experiments show motional heterogeneity for native glycinin, with a more uniform and restricted mobility after denaturation. Small angle scattering data show an expansion of -7% in the unit cell of the material as the moisture content is increased from 4.6% up to 13.4%, however there are no significant crystalline or other major structural changes in the protein over the spatial dimension probed (1-100 nm). © The Royal Society of Chemistry 2008.