Phosphate positioning and availability in the starch granule matrix as studied by EPR

Area of Science:

• Biophysical chemistry
• Carbohydrate chemistry
• Materials science

Background:

• Starch granules are complex carbohydrate structures with varying amylose and phosphate content.
• Understanding the interactions within starch granules is crucial for applications in food and biomaterials.

Purpose of the Study:

• To investigate the effect of phosphate on copper (Cu2+) binding within starch granules.
• To characterize the different copper adducts formed and their binding characteristics.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy was used to probe Cu2+ interactions.
• Starch granules were isolated from various potato genotypes, including modified ones with extreme amylose and phosphate levels.

Main Results:

• Multiple distinct copper adducts were identified, binding to the starch matrix with varying strengths.
• Phosphate content significantly influenced the type, number, location, and binding strength of copper species.
• In phosphorylated starch, well-dispersed Cu2+ complexes with axial symmetry formed in semicrystalline regions via O-P bonds.
• In amorphous regions, freely rotating hexaaqua Cu2+ complexes and antiferromagnetically coupled complexes were observed, with hexaaqua complex abundance increasing with phosphate content, indicating enhanced water binding.

Conclusions:

• Phosphate plays a critical role in modulating the microenvironment within starch granules.
• The findings provide insights into the location and effects of phosphate and crystalline matter on starch structure.
• This research complements existing experimental and molecular models of starch granule organization.