Partition of Main and Trace Minerals in Milk:  Effect of Ultracentrifugation, Rennet Coagulation, and Dialysis on Soluble Phase Separation

A study was carried out on the effect of soluble-phase separation on mineral distribution in milk. Fractioning was carried out by rennet coagulation (RC), ultracentrifugation (UC), and dialysis (D) against a large volume of water (1:10). Reconstituted skim milk powder was used and calcium, magnesium, sodium, potassium, phosphorus, manganese, zinc, citrate, lactose, and nitrogen were determined in the soluble fraction. The results of the first two procedures were comparable, except for Zn, which was lower in RC; greater precision was achieved with UC, especially for manganese. On fractioning by dialysis, Ca and Zn levels in the diffusate were higher than in the soluble fractions obtained by UC and RC as a result of long dialysis times (24 h) and low operating temperature (5 °C). With dialysis, Na and K levels in the diffusate were lower than with the other procedures. Of the three procedures assayed, UC appeared to be the best suited for work in series.