Biomacromolecules 2008, 9, 2937–2946
2937
Structure and Molecular Mobility of Soy Glycinin in the Solid State Catherine S. Kealley,† Manoj K. Rout,‡,| Mahshid Roohani Dezfouli,‡,| Ekaterina Strounina,§,| Andrew K. Whittaker,§ Ingrid A. M. Appelqvist,‡,| Peter J. Lillford,| Elliot P. Gilbert,*,† and Michael J. Gidley*,§ Bragg Institute, Australian Nuclear Science and Technology Organization, PMB 1, Menai, NSW 2234 Australia, Food Science Australia, Riverside Corporate Park, North Ryde, NSW 2113 Australia, The University of Queensland, St. Lucia, Brisbane, QLD 4072 Australia, and CSIRO Food Futures Flagship, North Ryde, NSW 2113 Australia Received July 2, 2008; Revised Manuscript Received August 21, 2008
We report a multitechnique study of structural organization and molecular mobility for soy glycinin at a low moisture content (17%) than DSC or SAXS, which sample for much longer times (∼10 to 103 s) and where changes are detected at >13% water content at 20 °C. The mobility transitions are accompanied by small changes in unit-cell parameters and IR band intensities and are associated with the enhanced motion of the polypeptide backbone. This study shows how characteristic features of the ordered regions of the protein (probed by SAXS and FTIR) and mobile segments (probed by NMR and DSC) can be separately monitored and integrated within a mobility transformation framework.
Introduction The behavior of proteins at a low moisture content (MC) is critical in understanding their storage and recovery after drying or freezing and their performance as materials in films, coatings, barriers, and low-moisture foods. In general, previous literature shows water-modulated changes in conformational structure, enzyme activity, particle swelling, and glass-to-rubber transitions.1-3 Molecular studies tend to be directed toward conformational changes that are related to enzyme activity2 or toward the investigation of low-temperature (200-220 K) transitions in the presence of excess water.4-7 Mobility (glass-to-rubber) transition temperatures increase with decreasing water levels because of reduced plasticization1 such that under ambient conditions, they typically occur at
