Diffusion of solutes in model cheeses as affected by cheese microstructure and physicochemical characteristics of solutes

Diffusion phenomena in cheeses are crucial to control their transformation and stabilization and then to maintain desired textural and sensorial properties. However, these phenomena are still not fully understood for solutes other than salt and water in cheeses. The aim of this work was then to investigate how solute diffusion is influenced by both microstructure of model cheeses and physicochemical characteristics of solutes. The model cheeses presented the same casein concentration (130 g.kg-1) but their microstructure was modulated by different technological treatments. A high-pressure freezing coupled with a freeze-substitution protocol was applied prior to Transmission Electron Microscopy (TEM) in order to minimize any modification of cheese microstructure. An automated image analysis procedure was developed to determine microstructural parameters from TEM images including pore size, interface area, particle size, inter-particle distance and tortuosity. Model solutes such as dextrans, proteins and peptides were used for their various properties of shape (flexible/rigid) and charge (neutral/negative/positive) in a wide range of molecular weights (from 4 to 2000 kDa). Their diffusion coefficients were determined using the innovative Fluorescence Recovery After Photobleaching (FRAP) technique. The diffusion phenomena were explained by microstructural parameters of model cheeses, mainly pore size and interface area between solutes and the surrounding matrix. However, the influence of the physicochemical characteristics of solutes on diffusion was more pronounced than that of the cheese microstructure and were related to the solute flexibility. Now, mathematical models will be developed to predict diffusion behaviour from both microstructural parameters of cheeses and physicochemical characteristics of solutes.