Mathematical modelling of salt diffusion in dry-salted cheese : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering at Massey University, Manawatu, New Zealand

Abstract

Control of salt uptake into cheese curds is vital to the production of safe, functional, and consistent cheese products. Development of mathematical models describing the mechanisms affecting salt uptake, namely the Fickian diffusion of salt into curds and osmotic pressure differential induced whey expulsion, are necessary to control curd properties, optimize salt uptake, and reduce final product inconsistency in commercial cheesemaking plants. Novel image analysis techniques were developed to assess whey expulsion behaviour in individual model renneted skim milk gels under different brining conditions. Whey expulsion results were combined with salt uptake data to develop mechanistically-derived mathematical models of the simultaneous whey expulsion and salt uptake under brining conditions. Whey expulsion data was combined with gel meso-structural properties to estimate the pressure gradients driving the whey expulsion behaviour. Finally, the simultaneous salt uptake and whey expulsion models were used to model salt and whey transport in model renneted gels treated under different dry salting conditions and compared to samples collected from an industrial cheesemaking plant. This work developed new techniques to evaluate whey expulsion in individual curds, demonstrated the importance of accounting for whey expulsion in the evaluation of salt uptake and modelling, and applied mathematical models describing simultaneous salt uptake and whey expulsion to milk gels exposed to brining and dry salting conditions.