Sensitivity of emulsions stabilised by bovine β-casein and lactoferrin to heat and CaCl2

Lactoferrin and b-casein represent a large proportion of the proteins in human milk and, as a result, are important ingredients for the manufacture of infant formula. At pH 7, lactoferrin has a net positive charge, compared to the negatively charged beta-casein. The effects of CaCl2 and heat treatment on the stability of oil-in-water emulsions stabilised by lactoferrin and/or beta-casein were investigated. The z-potential values of emulsions stabilised with b-casein or a 1: 1 mixture of beta-casein/lactoferrin significantly (P < 0.05) decreased on addition of 30 mM CaCl2, while CaCl2 had no significant (P > 0.05) effect on the z-potential of lactoferrin-stabilised emulsions. Particle size of beta-casein-stabilised emulsions increased significantly (P < 0.05) upon the addition of 30 mM CaCl2, due to flocculation, while emulsions stabilised with lactoferrin and beta-casein/lactoferrin remained unaffected by CaCl2 addition. Oscillatory rheology measurements showed that b-casein-stabilised emulsions formed a gel when CaCl2 was added, due to calcium-bridging, compared to lactoferrin-stabilised emulsions, where a weaker gel was formed in the presence of CaCl2. While, 30 mM CaCl2 did not increase the elastic modulus (G') of beta-casein/lactoferrin-stabilised emulsions. Lactoferrin protected beta-casein from calcium-induced flocculation by: (1) binding calcium ions via sialic acid groups on lactoferrin molecules and reducing the number of free ions available to form calcium linkages between beta-casein molecules; (2) electrostatically interacting with negatively charged phosphate groups on beta-casein molecules, blocking calciumephosphate interactions and (3) providing additional stability through increased steric repulsion between beta-casein/lactoferrin conjugates, due to the large molecular size of lactoferrin. (C) 2013 Elsevier Ltd. All rights reserved.