Effect of protein content of milk on the storage and loss moduli in renneting milk gels

A series of skim milks was made up with protein levels in the range 3 to 5 g/100g using ultrafiltration. The rheometric behavior during renneting was measured using low-amplitude oscillatory shear. Gel times were determined in terms of storage modulus G', loss modulus G" and tan delta (=G"/G'), respectively and were modelled in terms of protein level and enzyme level. Coagulum cutting time was defined in terms of G'. A prediction equation was developed for coagulum firming time in terms of gel time and protein level. The consistency of ultimate tan delta, over the range of protein and milks, showed that G" at coagulum cutting was related to G' and hence an on-line system could monitor coagulum firming rate by sensing either G' or G", or any related parameter, such as viscosity or complex modulus.