Rennet-induced coagulation is the basis for the productionof many cheese types. The coagulation occurs in two distinct phases. The first is the proteolytic cleavage of j-caseinat the Phe105–Met106bond to produce a glycomacropeptideand para j-casein, while the second is a calcium- induced aggregation of the para-casein into a three-dimensional protein network. It is believed that the calcium ions neutralisethe negative charges on the casein micelles, thereby facilitating hydrophobic interactions between the micelles and for-mation of the coagulum (Dalgleish 1992).
Removal of calcium from milk using ion exchange (Carret al. 2003), electrodialysis (Uchida et al. 1992) or chelating agents (Udabage et al. 2001) followed by renneting produces a noncoagulating milk which can be subsequentlycoagulated on addition of calcium. Such noncoagulati ngrenneted milks can be concentrated and/or dried and used inproducts such as processed or analogue cheeses (Carr et al.2003; Harvey et al. 2006).Sandra and Corredig (2013) showed that renneted recon-stituted milk protein concentrate had a lower rennet coagulation time (RCT) and increased gel firmness (as measured byG0, the storage modulus, after 45 min) when reconstituted in water containing 2.72 mM calcium chloride. Furthermor e,coagulation occurs at a lower level of j-casein hydrolysis with added calcium. Similarly, calcium chloride is routinelyadded during the manufacture of renneted cheeses todecrease the RCT and increase curd firmness. Additions upto 10 mM decreased RCT and incre ased gel strength, buthigh additions (>100 mM) had the opposite effect