Mineral and casein equilibria in milk: effects of added salts and calcium-chelating agents

Abstract

S. We have investigated the effects of adding a range of mineral salts and calcium-chelating agents on the distribution of casein and minerals between the nonpelleted and pelleted phases of milk obtained upon centrifugation at 78 000 g for 90 min. Adding CaCl # or mixtures of NaH # PO % and Na # HPO % to reconstituted skim milk (90 g milk solids\kg) at pH 6n65 increased both pelleted casein and pelleted calcium phosphate. Opposite effects were obtained by adding citrate or EDTA. The change in pelleted calcium phosphate was not simply related to casein release from the micelle. Upon adding 5 mmol EDTA\kg milk, 20 % of the pelleted Ca, 22 % of the pelleted phosphate and 5 % of the micellar casein were removed. Increasing the concentration of EDTA to 10 mmol\kg milk decreased the pelleted Ca by 44 % and the pelleted phosphate by 46 %, and caused 30 % of the micellar casein to be released. The effects of adding phosphate, citrate or EDTA at pH 6n65, followed by the addition of CaCl # , demonstrated the reversibility of the dissolution and formation of the micellar calcium phosphate. There were limits to this reversibility that were related to the amount of colloidal calcium phosphate removed from the casein micelles. Adding CaCl # to milk containing 20 mmol EDTA or 30 mmol citrate\kg milk did not result in complete reformation of casein micelles. Lightscattering experiments confirmed that the dissolution of moderate amounts of colloidal calcium phosphate had little effect on micellar size and were reversible, while the dissolution of larger amounts of colloidal calcium phosphate resulted in large reductions in micellar size and was irreversible.

Physicochemical characterization of calcium-supplemented skim milk

“…However, the average diameters of casein micelles were constant. In agreement with the study of Udabage et al [35], these results suggested that (i) there was no bridge between casein micelles after calcium addition, and (ii) casein micelles were able to incorporate caseins and ions and release water without detectable changes in their hydrodynamic diameters. Thus, from the increases in milk lightness and turbidity and in spite of the absence of variation in the average hydrodynamic diameter of casein micelles, we can suggest that the incorporation of ions and proteins into casein micelles and release of water from the casein micelles after calcium supplementation of milk increased the micellar density.…”

“…To describe the effects of calcium addition to milk, numerous physicochemical studies have been carried out [3,4,7,8,10,11,14,15,21,23,24,26,27,31,34,35,37,39]. These studies principally showed that addition of calcium to milk resulted in a new distribution of ions between milk serum and casein micelles, leading to physicochemical changes in casein micelles.…”

Skim milk powders with enhanced foaming and steam-frothing properties

“…At the levels of salts used, it is known that added calcium decreases serum casein content whereas the addition of phosphate or citrate which complex calcium has the opposite effect [18]. 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.…”

Calcium induced skim-milk gelation during heating as affected by pH

“…As is further seen from Table 1a, the addition of calcium chloride to skim milk (ECa) causes a slight increase of phosphorus in the serum phase, while as seen from Table 1b, the addition of calcium chloride (ECa) cause a decrease of phosphorus in the serum phase, after heating (Famelart et al 1999;Koutina et al 2015;Udabage et al 2000). The decreasing concentration of phosphorus in the serum phase after addition of calcium chloride and heating (Table 1b) can be understood from the low solubility of calcium phosphate in the serum phase upon heating and the tendency to form supersaturated solutions (Mekmene et al 2010).…”