Swelling and hydration studies on egg yolk samples via scanning fluid dynamic gauge and gravimetric tests

Hydration and swelling in initially dry protein-based samples represent the first stage in their cleaning from hard surfaces. These phenomena have been studied in technical egg yolk stains via scanning Fluid Dynamic Gauge (sFDG) and gravimetric tests. Temperature (30 °C to 55 °C) and pH (9.5 to 11.5) were investigated as factors influencing the process. The kinetics did not appear to be significantly different as 95% of the equilibrium swelling was reached at approximately 90 min in all tests. No removal of the egg yolk layer was observed in most cases, except at high alkaline conditions (pH 11.5), where a lift-up followed by a partial removal of the protein network was seen when an external shear stress was applied. The process mimicked creep behaviour of plastic materials. Gravimetric data on the hydration of the sample suggested a Fickian diffusion transport (Case I), where solvent diffusion is the rate limiting stage. The initial hydration was proved to be linear. Two diffusion theories of increasing complexity were applied to estimate effective diffusion coefficients: Fick's second law (with moving boundaries) and a non-linear poroelasticity theory. The temperature dependence of different diffusion coefficients assuming an Arrhenius equation gave an activation energy in the range of 16.4 (±6.7) KJ/mol to 18.4 (±9.0) KJ/mol.