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The effect of water content on the ordered/disordered structures in starches
T Y Bogracheva1, Y L Wang, C L Hedley
1John Innes Centre, Norwich Research Park, Colney, Norwich, NR4 7UH, UK. Tanya.Bogracheva@bbsrc.ac.uk
Biopolymers
|February 13, 2001
Summary
Nuclear Magnetic Resonance (NMR) reveals starch structure. Low water content significantly reduces double helices, especially in B-type starches, suggesting order stabilization.
Area of Science:
- Carbohydrate Chemistry
- Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy
- Materials Science
Background:
- Starch structure, comprising ordered (crystalline) and disordered (amorphous) regions, dictates its physical properties.
- Understanding the relationship between water content and starch structural organization is crucial for food science and materials applications.
- Solid-state NMR is a powerful technique for probing molecular dynamics and structural features in solid materials like starch.
Purpose of the Study:
- To investigate the influence of water content on the ordered and disordered structures of different starch types using (13)C cross-polarization magic angle spinning NMR.
- To characterize the structural differences between amorphous and ordered regions in starches as a function of hydration.
- To elucidate the role of water in stabilizing starch structural motifs, particularly double helices.
Main Methods:
- (13)C cross-polarization magic angle spinning NMR spectroscopy was employed to analyze starch samples.
- Samples were prepared with varying water content (1-50%).
- NMR spectral parameters (peak shape, width, position, and area) were analyzed to differentiate between ordered and disordered regions and assess structural changes.
Main Results:
- Amorphous starch regions yield NMR signals only in the glassy state, with peak characteristics sensitive to temperature and water content.
- Gaussian peak profiles were observed for amorphous regions, while Lorentz profiles characterized ordered regions.
- Water content between 10-50% did not affect the proportion of double helices.
- A significant reduction in double helices was observed at 1-3% water content, more pronounced in B-type than A-type starches.
Conclusions:
- Short-range ordered structures (double helices) in starch are stabilized by their integration into long-range ordered structures (crystallites).
- Water content plays a critical role in the stability of starch double helices, particularly at low hydration levels.
- NMR spectroscopy provides valuable insights into the complex structural organization of starches and the impact of environmental factors.