Microstructure of beta-lactoglobulin/pectin coacervates studied by small-angle neutron scattering

Area of Science:

• Food science and materials science
• Biopolymer interactions and self-assembly
• Colloid and interface science

Background:

• Beta-lactoglobulin/pectin coacervates are complex fluids with potential applications in food and pharmaceuticals.
• Understanding their microstructure is crucial for controlling their functional properties.
• Previous studies have explored various aspects of these coacervates, but detailed microstructural analysis under varying conditions is needed.

Purpose of the Study:

• To investigate the microstructure of beta-lactoglobulin/pectin coacervates using small-angle neutron scattering (SANS).
• To determine the influence of initial protein/polysaccharide ratio (r), sodium chloride concentration (C(NaCl)), and pectin charge density on coacervate microstructure.
• To elucidate the formation mechanisms of protein domains within these coacervates.

Main Methods:

• Small-angle neutron scattering (SANS) was employed to analyze coacervate samples.
• Coacervates were prepared with varying protein/polysaccharide weight ratios (r), sodium chloride concentrations (C(NaCl)), and pectin charge densities.
• Scattering data was analyzed to interpret structural features like scattering intensity and domain formation.

Main Results:

• Higher r and pectin charge density led to increased scattering intensity, indicating tighter pectin chain aggregation due to charge screening by proteins.
• A shoulder peak in the intermediate q-range indicated the formation of protein domains, with sizes estimated between 7.2-8.5 nm at higher r values.
• Increased C(NaCl) resulted in a broader and shifted shoulder peak, suggesting a more heterogeneous coacervate structure.
• Lower pectin charge density favored the formation of larger protein domains, potentially due to beta-lactoglobulin self-aggregation.

Conclusions:

• The microstructure of beta-lactoglobulin/pectin coacervates is significantly influenced by formulation parameters like protein/polysaccharide ratio, salt concentration, and pectin charge density.
• Protein domain formation is a key microstructural feature, influenced by electrostatic interactions and protein self-aggregation.
• Two distinct microstructural states, with and without observable protein domains, were proposed for these coacervates.