Short communication: Calcium partitioning during microfiltration of milk and its influence on rennet coagulation time

ABSTRACT Pasteurized skim milk was subjected to (1) microfiltration (MF) at 50°C and (2) MF at 6°C after storage at 2°C. The products of these treatments were retentate (RMF50) and permeate (PMF50), and retentate (RMF6) and permeate (PMF6), respectively. Additionally, RMF50 was subjected to (3) cold MF after water dilution to produce retentate (RMF6R) and permeate (PMF6R). Calcium migration was monitored by analyzing ionic, soluble, and total calcium content in feed, retentates, and permeates. The influence of calcium partitioning and calcium addition to feed, retentates, and retentates diluted with water was determined. Without CaCl 2 addition, only skim milk, RMF50, and RMF6 coagulated after rennet addition. Higher true protein and casein content of RMF50 and RMF6 resulted in shorter time of renneting. The retentates diluted with water showed no signs of coagulation within 40 min. The addition of PMF6R to RMF50 did not affect rennet coagulation time within the observed 40 min in comparison to RMF50 + water. In general, higher CaCl 2 addition resulted in shorter rennet coagulation time. Special attention should be paid to calcium partitioning during membrane processing of cheesemilk. The level of calcium addition should be adopted to calcium content in such cheesemilk, which is affected by conditions of the filtration process (i.e., concentration factor and temperature).