Disparate dynamic viscoelastic responses of wheat flour doughs coated with different oils for preventing water evaporation during time sweeps and their mechanisms decoupled.

Various non-volatile oils are currently applied in order to prevent water evaporation from exposed surface of dough during oscillatory measurements. A systemic understanding of their effectiveness in controlling water loss and ensuring accuracy of rheological measurements is necessary. In this work, three kinds of coating oils (vaseline, dimethyl silicone oil and low viscosity silicone oil) were selected to minimize water evaporation from dough of 37%, 42% and 47% water content subjected to time sweep tests under oscillatory mode. Evolution patterns of the storage modulus, loss modulus and loss factor with time were followed, and the mechanisms responsible for the response patterns were decoupled. Disparate dynamic viscoelastic responses were found for the same dough coated with different oils. Spontaneous de-structuring of dough combined with thixotropic effect contributed to the decrease of dynamic modulus and increase of the loss factor with time. Dynamic vapor sorption tests showed that water evaporation did occur for the dough even coated with non-volatile oils including vaseline. Water evaporation led to an accelerated increase in dynamic modulus with time, while had a very limited impact on loss factor. Oil invasion only played a minor role in the decrease in dynamic modulus. The measured modulus was actually a sum of the positive and negative contributions. Vaseline was observed as an effective coating oil for rheological measurements of dough, especially with high water content.