The influence of alkaline earth metal equilibria on the rheological properties of rennet-induced skim milk gels

Abstract

The mineral equilibria of milk can have a major influence on the properties of rennet milk gels. The influence of increased Mg, Ca, and Sr concentrations on milk and rennet milk gels was investigated. Reconstituted skim milk was supplemented with MgCl 2 , CaCl 2, or SrCl 2 at levels from 2.5–10 mmol.L −1 and adjusted to pH 6.6. Dynamic rheological properties of the renneted milks at 32 °C were investigated during 6-h time sweeps and by frequency sweeps. Whey was separated from rennet gels by centrifugation at the gelation point and also 6 h after rennet addition. The concentrations of Mg, Ca, Sr, and inorganic P in milks and wheys were determined. Levels of casein-bound Mg, Ca, and Sr increased with the addition of their respective chloride salt. The percentage of CN-bound inorganic P increased with the increasing concentration of each divalent cation. Milk gelation time decreased with the increasing concentration of each divalent cation salt. Milks containing 10 mmol.L −1 of CaCl 2 or 10 mmol.L −1 of SrCl 2 exhibited buffering capacities significantly higher ( P < 0.05) than the 10 mmol.L −1 of MgCl 2 and control milks. An increase in G ′ and a decrease in tan δ were observed in milk gels supplemented with the divalent cation salts. Milk gels supplemented with either CaCl 2 or SrCl 2 had superior rennet gel properties compared with MgCl 2 -supplemented milk gels (especially at low frequencies). This study provides information on the link between the mineral fortification of milk and modulation of milk gel properties and potentially for the mineral fortification of cheese.