EDTA-induced dissociation of casein micelles and its effect on foaming properties of milk

Abstract

The effects of addition of EDTA on the dissociation of caseins and foaming properties of milks (100 g solids/l) reconstituted from skim milk powders given a low-heat (72°C for 30 s) or high-heat (85°C for 30 min) treatment during powder manufacture were determined. The EDTA-induced dissociation of caseins was independent of heat treatment but in high-heat milk was accompanied by release of denatured whey proteins. EDTA changed the proportions of individual caseins in the supernatant. EDTA addition improved both foam overrun and foam stability of low- and high-heat milks. The increase in serum protein on addition of EDTA contributed to the improvement in foaming properties of milks by increasing the availability of the proteins for formation of the air–water interface.

Skim milk powders with enhanced foaming and steam-frothing properties

“…The improved foaming properties of milks with added phosphate or citrate and the depression of foam formation with added calcium can be attributed to changes in the availability of soluble caseins. The observed effects of added calcium complexing salts on foaming properties of milk corroborate those observed previously [12,20,21]. Figure 2 shows the effect of preheat treatment and citrate addition on the steam-frothing properties of milk (100 g solids·kg −1 ).…”

“…The effects of pH on foaming properties are in line with our previous work where milks of similar concentration (100 g solids·kg −1 ) and conditions of foaming were used [20]. With decreasing pH, the major effect is an increase in foam overrun whereas foam stability is more improved at high pH.…”

“…In the high-heat treated milk, the majority of the whey proteins are denatured and hence the air-water interface formed during frothing will be different from that formed when low-heat milk is steam-frothed. Previous work has shown that high-heat treatment causes ∼70% whey protein denaturation [20]. It was also shown that although there was a similar degree of casein dissociation in low-heat and high-heat treated milks caused by the addition of a chelating agent (EDTA), the dissociation of the highheat milk also caused dissociation of denatured whey protein from the micelle [4], leaving a micelle with different properties from a micelle in high-heat treated milk.…”

“…inherent nature of the protein) as well as extrinsic factors (e.g. pH, ionic environment and heat) influence the formation and stability of a foam [10,13,14,[20][21][22].…”

“…These results suggest that the caseins had to be available in the supernatant for adsorption to the interface. Improvement in foaming properties of milk was obtained with the addition of chelating agents such as hexametaphosphate [12] or EDTA [20] to milk systems. These chelating agents are known to cause release of caseins into the serum by dissociating the colloidal calcium phosphate within the casein micelles.…”