New Approach to Investigate the Quality of Parmigiano Reggiano Cheese: Multi-Scale Virtualization of the Structure and Analysis of Fundamental Rheological Properties

PDO Parmigiano Reggiano cheese was investigated for its structural changes, texture and rheology with the aim to better understanding process-structure-quality relationships. The typical quality requirement is described in the PDO disciplinary as “frattura a scaglie”, i.e. its ability to propagate a fracture triggered under controlled stress conditions. Cheese samples were provided by Consortium with different ripening stages then characterized by means of Electron Scanning Environmental Microscopy, X-ray Microtomography, Single-Edge Notch Bending, Stress Relaxation, Creep, Temperature and Frequency Sweep in Oscillatory tests. Results suggested that the fracture mode is strictly related to the heterogeneity of cheese structure over a large range of scale. The applied stresses concentrate around the tips of sub-micron discontinuities, this latter arise from partially fused curd junctions originated during milk clotting and cutting; consequently new surfaces originate and propagate along with the interfaces between fat and protein matrices due to their different relaxation times. The extent of crack propagation within the cheese bulk is limited by the presence of micro-voids, as well as by plastic and viscous dissipative forces both decreasing during ripening of the cheese. Flexture tests quantitatively described the extent of mode-I fracture. Creep and stress relaxation data were analysed to compare cheese samples by relaxation times. Finally, temperature and frequency sweep oscillatory tests provided quantitative pictures of both elastic recovery and viscous or plastic deformations. This research sets the basis for the optimisation of the making process of Parmigiano Reggiano, considering fracture requirements as a key quality driver in a reversed engineering approach