For calcium binding: Electrochemical method (calcium ion selective electrode) combined with quantum mechanical
calculations (density functional theory) were used to investigate the calcium binding affinity of the amino acids and small
glycine peptides. The effects of the ionic strength and pH on calcium binding affinity of the investigated amino acids were
discussed. It was found that only charged amino acids would be affected by ionic strength. The calcium binding affinity was
considerably improved by high pH inducted protonation of amino group. Moreover, a model was established to describe this
pH effect. Optimized structures of calcium amino acids or peptides complexes were obtained through density functional
theory calculations. The calculated calcium binding affinity is in agreement with the obtained experimental data. These
optimized structures provide the possible calcium binding mechanism by amino acids and peptides. In addition, amino acids
with strong calcium binding ability at high pH was found to have a calcium binding site shift from carboxylate binding to
chelation by α-amino group and carboxylate oxygen. Compared with calcium binding ability of the single amino acid,
synergistic effect in calcium binding was found for the small glycine peptide rather than amino acids mixtures with the
enhanced driving force up to -6 kJ/mol. Such study provides useful information for the future development of calcium
supplements.
For zinc binding: Isothermal titration calorimetry was applied to investigate the zinc binding affinity of amino acids,
peptides and whey proteins. Cysteine and histidine are strong zinc binders, while aspartic acid and glutamic acid need to
combine nitrogen donor or sulfur donor to facilitate zinc binding. Enthalpy entropy compensation effect was observed for
zinc binding by the investigated amino acids, peptides and proteins. The thiol group or imidazole group containing amino
acids, peptides and proteins which exhibited strong zinc binding ability were further selected for interacting with zinc salts
in relation to zinc absorption. The interactions between the above selected food components and zinc citrate or zinc phytate
will lead to the enhanced solubility of zinc citrate or zinc phytate. The main driving force for this observed solubility
enhancement is the complex formation between zinc and investigated food components as revealed by isothermal titration
calorimetry and quantum mechanical calculations. This is due to the zinc binding affinity of the relatively softer ligands
(investigated food components) will become much stronger than citrate or phytate when they present together in aqueous
solution. This mechanism indicates these food components induced solubility enhancement will improve the zinc bioavailability. Moreover, a mathematical model established from the studies of human absorption of zinc was applied to
quantify the effect of the enhanced zinc phytate solubility on zinc absorption. Histidine and citrate are very promising
ligands for improving zinc absorption from phytate rich foods. Such study provides a better understanding of zinc binding
by the food components which can be used for improving zinc absorption.
For iron binding: The iron(IV) binding protein, ferrylmyoglobin, was investigated for the iron binding study. Tyrosine
based food components were selected to reduce the ferrylmyoglobin. Different reaction pathways were proposed according
to the multivariate curve resolution analysis. The reduction kinetics was obtained through hard modelling of the spectral
data obtained from stopped flow spectroscopy. The pH was found to affect the reaction kinetics considerably. In addition,
the reaction mechanism was investigated through quantum mechanical calculations. According to the density functional
theory calculated quantity descriptors, sequential proton loss electron transfer seems to be the reaction mechanism for the
reduction of ferrylmyoglobin by tyrosine based food components. Moreover, based on the obtained thermodynamic
parameters that relevant for reduction of ferrylmyoglobin, the quantitative structure activity relationship model for reducing
ferrylmyoglobin by tyrosine based food components were established by applying partial least square regression. Such
study provides useful information for developing muscle foods.