Screening for metal chelating activity in potato protein hydrolysates using surface plasmon resonance and peptidomics

Abstract: Lipid oxidation is, among other factors, catalyzed by the presence of metal ions and efficient metal chelators are therefore highly sought after in the food industry. Due to increasing consumer demand for natural, plant-based and “clean-label” ingredients, natural metal chelators are gaining interest as opposed to their synthetic counterparts such as EDTA. Traditional screening for metal chelation capacity can be either time consuming or non-specific. The aim of this study was to investigate if there is a correlation between the equilibrium dissociation constant (K_D) between a hydrolysate and Ni²⁺ and the antioxidant activity of the hydrolysate in an emulsion system containing Fe²⁺. Surface Plasmon Resonance (SPR) is a label-free, optical technique used to determine the K_D of a complex formed between immobilized Ni²⁺ and an analyte. In this study, hydrolyzed potato protein was fractionated using ultrafiltration. Unfractionated hydrolysates were included as well. The freeze-dried hydrolysates were used as antioxidants in 5% oil-in-water emulsions stabilized with Tween 20. Fe²⁺ was added to initiate the oxidation. The oxidative stability of the emulsions was evaluated during 9 days of storage at room temperature and benchmarked against a control without any antioxidants and EDTA. The affinity of the hydrolysates for Ni²⁺ at pH 7.4 was evaluated using SPR and peptidomics was used to determine, which peptides were present in each of the fractions. The (K_D) were determined for all hydrolysates. The K_D values are similar to previous studies on hydrolysates indicating metal chelating activity. All hydrolysate samples performed better than the control, but worse than EDTA, in terms of peroxide value and formation of secondary volatile oxidation products. The results of this study indicate that there is a connection between the affinity for Ni²⁺ in SPR and the iron chelating activity in emulsions.