The increasing interest in understanding positive effect of milk protein hydrolysates on calcium bioavailability have led to identification of several peptides as calcium chelators during the last decades. As a new perspective, binding strength rather than binding capacity has been introduced to quantify the potential of individual peptides. Binding strength expressed as association constants for calcium complexes with relevant peptides and their temperature dependence has been determined electrochemically for the Gly-Tyr and Tyr-Gly peptides in aqueous solution using a calcium selective electrode. The two peptides showed very different pH profiles for their calcium binding, which was confirmed by quantum mechanical calculations within the Density Functional Theory (DFT). DFT calculation showed one more hydroxyl group was involved in calcium binding to Tyr-Gly compared to Gly-Tyr. For pH corresponding to milk under digestion, Gly-Tyr binds calcium stronger than Tyr-Gly, with a Kass of 400 L/mol for Gly-Tyr compared to 200 for Tyr-Gly at 25 oC around pH 7, both with exothermic calcium binding. The two dipeptides also show different antioxidant effect sensitive to presence of calcium, which could be understood by different electron distribution and calcium binding pattern. The relative oxygen concentration for both Gly-Tyr and Tyr-Gly added alone or with CaCl2 in an aqueous methyl linoleate emulsion with myoglobin as a catalyst at 25 oC showed that Tyr-Gly was more effective delaying oxygen depletion than Gly-Tyr and calcium addition remarkably accelerated the oxygen consumption for Tyr-Gly. The scavenging kinetics of the semistable radical ABTS+● study by stopped-flow absorption spectroscopy at 25 oC confirmed that the rate of ABTS+● scavenging decreased by addition of CaCl2, corresponding to radical scavenging rate 3.03 × 10−2 s−1 for Gly-Tyr compared with 1.93× 10−2 s−1 for Gly-Tyr with CaCl2.

Calcium binding to peptide from whey protein hydrolysis

ACS Fall 2021

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