Calcium release from milk concentrated by ultrafiltration and diafiltration.

The present work studied the solubilization of Ca during acidification in milk concentrated by ultrafiltration (UF) and diafiltration (DF). The effect of heating milk at 80°C for 15min was also evaluated. In addition to measuring buffering capacity, the amount of Ca released as a function of pH was determined. The area of the maximum peak in buffering capacity observed at pH ~5.1, related to the presence of colloidal Ca phosphate, was significantly affected by casein volume fraction but did not increase proportionally with casein concentration. In addition, a lower buffering capacity and less solubilized Ca were measured in 2× DF milk compared with 2× UF milk. Heat treatment did not change the buffering capacity or Ca release in 1× and 2× concentrated milk. On the other hand, at a higher volume fraction (4×), more Ca was present in the soluble phase in heated 4× UF and DF milk compared with unheated milk. This is the first comprehensive study on the effect of concentration, distinguishing the effect of UF from that of DF, before and after heating, on Ca solubilization.