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 ϑ process . It was shown that ϑ process should be set according to the following relation: ϑ gel-sol (full plasticization) ≤ ϑ product ≤ ϑ tanδmax (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, ϑ process  = 63 °C and SS  = 10 rpm. Experiments using fermented and ripened cheese curd (pH 5.0) corroborated the proposed process design strategy.