Mathematical modelling of the formation of rennet-induced gels by plant coagulants and chymosin

Rheological properties of reconstituted skim milk coagulated with plant coa gulants Cynara cardunculus L., Cynara humilis L. and chymosin was monitored by dynamic low amplitude oscillation. There are no published reports on th e modelling of the gelation behaviour of milk by plant coagulants. Three ma thematical models. Scott Blair, Douillard and Carlson, were fitted to the s torage modulus (G') as function of time curves. For all coagulants, Scott B lair model was the most efficient in modelling the gelation process, and ga ve both the smallest residuals and standard error of residuals, Se (P<0.000 1). Douillard model gave the poorest fit and in particular it was not able to predict the initial part of the gelation curves. Carlson model had an in termediate behaviour and, in the case of chymosin, it gave results that wer e quite comparable to Scott Blair model. The parameters of the Scott Blair model were different for plant coagulants and chymosin. Chymosin had the lo ngest rate constant (<tau>) and the time shift coefficient (t(s)) was also different between vegetable coagulants and chymosin (P<0.0005). These resul ts are in agreement with the overall trends for gelation profiles obtained for vegetable coagulants and chymosin. In the beginning of gelation both pl ant coagulants produced gels With slightly higher G' values than chymosin, but after longer incubation times chymosin gels had higher G' values. It wa s concluded that the Scott Blair model was the best equation to follow the gelation of milk induced by both plant coagulants as well as chymosin. Mode lling is an important and useful method for comparing the gelation process in gels formed by different ty es of coagulants.