The stretching process of Mozzarella plays an important role in creating the unique fibrous texture of mozzarella cheese. The most used stretching equipment is the twin-screw cooker-stretcher with recirculating hot water.
During the combined cooking and stretching process in cooker-stretcher, phase transition, compositional loss and structure formation occur in mozzarella curd. This study aims to investigate the interaction of cooker-stretcher parameters, e.g. water temperature (WT) and screw speed (SP), and the separate contribution of the cooking and stretching processes on mozzarella cheese composition, structure and rheological properties. In this study, the cooker-stretcher was divided into two sections: the initial part that is filled with water (cooking section) and a second part without water (stretching section).
The effects of WT and SP, and their interactive effects on the residence times of the curd in the two sections, i.e. cooking residence time (CRT) and stretching residence time (SRT), were linked to mozzarella cheese composition, micro- and macro structural characteristics. Increased WT resulted in longer CRT and SRT while increased SP led to shorter CRT and SRT. The interaction between WT and SP was significantly reflected in CRT and SRT based on factorial design analysis. Linear correlations were found between CRT and cheese composition, anisotropy and storage modulus. Non-linear relationships were observed between CRT and SRT and fat globule size.
In general, SRT had a less significant effect on cheese properties, which may be due to the low shearing that occurred in this specific equipment used. Residence times CRT and SRT were identified as relevant factors to evaluate cooker-stretcher equipment and to further understand the structural formation of mozzarella cheese during manufacture.
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