Effects of calf rennet, and microbial and plant coagulants on rheological properties of milk for Grana Padano PDO cheese production

The effects of calf rennet, and microbial and plant coagulants on milk coagulation properties (MCP) measured through lactodynamographic analysis were investigated. Each coagulant was tested at 7 different dilutions: one reference dilution, 3 lower dilutions (-30%, -20%, and -10% IMCU L-1 milk) and 3 greater dilutions (+10%, +20%, and +30% IMCU L-1 milk). Sources of variation of rennet coagulation time (RCT, min), curd-firming time (k20, min), and curd firmness (a30, mm) were investigated through a linear model that included the effects of coagulant, dilution, and their interaction. All the effects were highly significant in explaining the variability of the studied traits (P <0.001). In particular, calf rennet resulted in shorter k20 and greater a30 than microbial and plant coagulants. Dilution effect was linearly associated with MCP, whereby a decreasing amount of coagulant led to a lengthening of RCT and k20, whereas a less clear association was observed for a30.