The effects of different cations on the physicochemical characteristics of casein micelles

Physicochemical characterisation of casein micelles suspended in milk ultrafiltrate and enriched with different cations (Fe, Cu, Ca, Zn and Mg) was investigated. After addition of 2.5-8.0 mmol kg(-1) of cations, associations of added cation, citrate, inorganic phosphate and calcium with casein micelles were observed. The order of association of cations with casein micelles was Fe3+ > Zn2+ > Ca2+ > Cu2+ > Mg2+. At the same time, the casein content increased in the casein micelles while the water content decreased. Changes in hydrophobicity and zeta potential of casein micelles were also determined while no variation in the average diameter was detected. In the presence of 8.0 mmol kg(-1) of magnesium or ferric iron, heat stability (115 degreesC for 30 min) of casein micelles was decreased. From these results, a mechanism of cation association with casein micelles is proposed, highlighting the determinant role of ultrafiltrable citrate and inorganic phosphate. This mechanism is discussed in relation to modifications in physicochemical characteristics of casein micelles. (C) 2004 Elsevier Ltd. All rights reserved.