An entropy-centric equilibrium cooperative theory for the melting behaviour of non-ideal triglyceride mixtures

Abstract: A new non-ideal, equilibrium thermodynamics model was developed for the extrapolation of the solid fat content (SFC) of edible fats, which are mixtures of triaclylglycerols (TAGs). The SFC is the most dominant material structural parameter which influences macroscopic mechanical properties and functionality in foods, cosmetics and pharmaceutical incipients. By taking into consideration the entropy of mixing and the activity coefficient of a TAG in an effective solid medium, we calculate a freezing point depression. The new melting point is then nested into an equilibrium expression for the melting of that TAG in such effective solid medium. The model considers that complex mixtures of TAGs consist of one solid phase in a specific polymorphic form and one liquid phase, obeying mass balances and the overall TAG composition determined experimentally. The SFC is then just the summation of the amount of solid TAG components in the mixture. Novel insights are gained from estimates of a cooperativity index for the melting of the different TAGs in the effective solid medium, while estimated solid-state activity coefficients speak to interactions of particular TAGs with the effective medium. The model was successfully fitted to eight different SFC-temperature profiles of complex fats and parameter estimates obtained and interpreted.

The activity coefficients were found to be quantitatively related to the cooperativity index. Thus, for full prediction ability, only the activity coefficients for the TAGs in the solid state need to be estimated, for which formalisms exist.