Food Research Institute

Udenigwe, C. C. – Gong, M. – Mohan, A. – Udechukwu, M. C.
Role of surface charge of hydrolysed bovine caseins in their iron(II)-binding affinity and antioxidative capacity in iron(II)-facilitated beta-carotene and glutathione oxidation
Journal of Food and Nutrition Research, 56, 2017, No. 2, s. 149-154

Chibuike C. Udenigwe, School of Nutrition Sciences, Faculty of Health Sciences, University of Ottawa, 25 University Private, Ottawa, Ontario, K1N 6N5, Canada; Department of Plant, Food, and Environmental Sciences, Faculty of Agriculture, Dalhousie University, 50 Pictou Road, Truro, Nova Scotia, B2N 5E3, Canada. E-mail: cudenigw@uottawa.ca

Received 2 December 2016; 1st revised 16 February 2017; accepted 11 March 2017; published online 3 May 2017

Summary: Surface properties of peptides can affect their functionality, including metal-binding capacity. Casein hydrolysed with five proteases had varying surface hydrophobicity (from 56.4 ± 3.1 to 157.0 ± 16.8) and surface charge (zeta-potential, from –43.5 mV ± 0.5 mV to –32.5 mV ± 0.6 mV). The hydrolysates had varying Fe²⁺-chelating capacity (from 0.049 mg·ml^-1 ± 0.005 mg·ml^-1 to 0.134 mg·ml^-1 ± 0.027 mg·ml^-1); the best activities were observed for hydrolysates with the highest surface hydrophobicity. Maximum specific ligand binding (B_max) of the samples appeared to be independent of surface charge and hydrophobicity. However, ligand dissociation constant (K_d) of the peptide-Fe²⁺ complex strongly correlated with zeta-potential (r_s = 0.90). This suggests that the negatively charged surface of the particles facilitated peptide-Fe²⁺ chelate complex formation via electrostatic interaction. Casein hydrolysates with the lowest K_d and zeta-potential displayed the maximum capacity for inhibiting Fe²⁺-facilitated oxidation of beta-carotene, suggesting that strong Fe²⁺-binding by the peptides made the pro-oxidant metal less available for participation in oxidation. However, this relationship was not observed for their inhibition of Fe²⁺/H₂O₂-induced glutathione oxidation, likely due to peptide inaccessibility to the anionic glutathione. The findings show that surface chemistry of hydrolysed caseins affects their interactions with pro-oxidant iron, which is an important consideration for their use as antioxidants in foods.

Keywords: casein hydrolysate; iron chelation; beta-carotene oxidation; glutathione oxidation; binding affinity; surface charge

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