Polysaccharides crystal systems

Cellulose has been dissolved in A-methylmorpholine iV-oxide at high temperature and the recrystallization of the polysaccharide upon cooling investigated." The crystallization system is analogous to the solidification of binary mixtures of polymer and diluent, which present unusual thermodynamic and morphological properties. The system provides a new method of texturing cellulose. 

Marchessault, R.H., Morehead, F.F., Walter, N.M. Liquid crystal systems from fibrillar polysaccharides. Nature. 184, 632-633 (1959a)... 

The glass transition processes in foods may result from a rapid removal of water from solids. Based on that, e.g., the Tg values of anhydrous polysaccharides are high, and the food materials may decompose at temperatures below Tg (Kokini et al 1994 Roos and Karel, 1991b). The glass temperature transition affects viscosity, stickiness, crispness, collapse, crystallization, and ice formation, and can strongly influence deteriorative reaction rates. This provides a new theoretical and experimental framework for the study of food systems to unify structural and functional aspects of foods, described in terms of water dynamics and glass dynamics. 

Biological macromolecules such as polysaccharides, fibrous or membrane proteins characteristically adopt a unique secondary structure which may be related to a variety of physical or biological properties. Elucidation of the three-dimensional structure of these systems is not always straightforward, because, in many instances, they are insoluble in ordinary solvent systems, and crystallization for X-ray diffraction study is extremely difficult. A possible disruption of a particular secondary structure should also be anticipated, when they are solublized in a solvent or detergent. Therefore it is essential to clarify their secondary structures either in the solid, gel or membrane-bound state without any attempt at solubilization. 

Meer et al. [54] listed five primary functions of nonstarch polysaccharides in food systems retention of water, reduction in moisture evaporation, alteration of freezing rate, modification of ice crystal formation, and regulation of rheological properties or viscosity. 

Xanthan gum is an anionic polysaccharide secreted by certain bacteria which in the dry state does not exhibit a first-order phase transition. In the presence of a small amount of water a glass transition, cold crystallization, melting and a liquid crystal transition are observed. Figure 5.28A presents DSC heating curves of water-xanthan gum systems with various water contents. A 3 mg sample was hermetically sealed in an aluminium sample vessel, cooled from 320 to 150 K at 10 K/min and subsequently heated at 10 K/min. With reference to Section 5.1, the transition temperatures are defined as follows glass transition temperature and melting and crystallization temperatures 7p and, respectively. The... 

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