In recent times, various research on thickeners and perceptions of flavours in sauces and food in general, have uncovered that thickeners reduce our perception of flavour molecules and saltiness. A very interesting one on viscosity and flavour perception, conducted by A. L. Ferry, J. Hort, J. R Mitchell, S. Lagarrigue and B.V. Pamies from Division of Food Sciences University of Nottingham Sutton Bonington, Loughborough in the U.K. and the division of Nestlé Product Technology Center in Germany has shown that viscosity has a huge influence on the perception of salt by our taste buds.
The first reason why the perception of salt by our taste buds is reduced, is that starch based thickeners increase the level of amylose into our mouth. Amylose has the property to trap aroma molecules and bind salt molecules thus decreasing aromatic intensity and saltiness.
Secondly, this study shows that viscosity (the property of a fluid that resists the force tending to cause the fluid to flow) influence the way our taste buds sens salt. It seems that our brain is too busy dealing with this sensation that the salt perception is decreased.
Finally, it appears that poly-saccharides (long-chain carbohydrates), like starch, are able to bind sodium ions to themselves, resulting in a reduction of saltiness.
As a result, the reduction of saltiness reduce the overall aroma intensity in our mouth, albeit the fact that the same number of aroma molecules are flowing out of the sauce and across the smell receptors in our nasal passages. So, if using flour or starch based thickeners, such as a roux or arrow root, in your sauce, you must think that its overall flavour will be diminished. It is, therefore, very important to taste your sauce and rectify, to some extent, its flavour by adding more salt at the end of its cooking process.