Zinc bioavailability from whey. Enthalpy-entropy compensation in protein binding.

Area of Science:

• Biochemistry
• Nutritional Science
• Physical Chemistry

Background:

• Zinc absorption is enhanced by amino acid or peptide complexes, but the thermodynamics of zinc-ligand interactions are not well understood.
• Food components like phytate can reduce zinc bioavailability, necessitating strategies to improve zinc absorption.
• Understanding zinc binding thermodynamics is crucial for developing effective zinc supplements and fortified foods.

Purpose of the Study:

• To investigate the thermodynamics of zinc ion binding to various amino acids, peptides, and whey proteins.
• To provide data for improving zinc bioavailability and stability in food matrices.
• To elucidate the role of enthalpy-entropy compensation in zinc-ligand interactions.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to measure the binding thermodynamics of zinc ions.
• Zinc binding was studied with individual amino acids, model peptides, and whey proteins (lactoferrin, bovine serum albumin, α-lactalbumin, β-lactoglobulin).
• Experiments were conducted in aqueous solutions (0.16M NaCl, pH 7.4, 25°C).

Main Results:

• Zinc binding to lactoferrin and bovine serum albumin was exothermic (ΔH = -100 kJ/mol and -30 kJ/mol, respectively).
• Zinc binding to α-lactalbumin and β-lactoglobulin was slightly endothermic.
• Binding constants for all four proteins were approximately 2×10⁵ L/mol, indicating enthalpy-entropy compensation.
• Enthalpy-entropy compensation was also observed for zinc binding to amino acids, with varying contributions from enthalpy and entropy.

Conclusions:

• Enthalpy-entropy compensation plays a significant role in zinc binding to whey proteins and amino acids.
• This compensation mechanism enhances the homogeneity of whey proteins as zinc carriers, preventing fluctuations and precipitation.
• The findings offer valuable insights for optimizing zinc bioavailability through protein-based delivery systems.