Waterless single screw extrusion of pasta-filata cheese: Process design based on thermo-rheological material properties

Abstract

Process design of a waterless single screw extrusion of pasta-filata cheese was established based on the material properties during the major steps plasticization, conveying and texturization. Thermo-rheological properties of model cheese curds (pH 5.8 adjusted by citric acid) were determined by small amplitude oscillatory strain experiments (20 – 80 °C) to narrow a promising range of the process temperature ϑprocess. It was shown that ϑprocess should be set according to the following relation: ϑgel-sol (full plasticization) ≤ ϑproduct ≤ ϑtanδmax (peak flowability). Critical shear rates (γ˙crit) of plasticized model cheese were analyzed by a capillary rheometer and translated to the screw speeds (SS) by considering the default configuration of the waterless extruder. Upscaling of process conditions was evaluated with regards to product homogeneity and chemical composition, resulting in the most promising parameters, ϑprocess = 63 °C and SS = 10 rpm. Experiments using fermented and ripened cheese curd (pH 5.0) corroborated the proposed process design strategy.