Thanks for moving a step further towards the learning on lecithin. Exact degrdation temp could be difficult aspect since it contains a mixture of molecules. Some details that might be relevant to your query:::
Lecithin is composed of various phospholipids (PLs), abundant being phosphatidylcholine (PC) and phosphatidylethanolamine (PE). soybean lecithin is prone to oxidation, sensitive to heat and light, which restricts its application in industries. As known from its structure, the fatty acid composition of lecithin affect/ determines the stability. Some details shows that phospholipids remain unchanged at temperatures up to 100°C, though color changes are known. If triglycerides and PLs are removed, a huge difference in aroma might occur, and probably structural phospholipids are essential for specific aroma.
As per literature, Lecithin is useful for enhancing the heat stability of emulsions, due to interactions between lecithin and proteins. How about using materials like CD (Cyclodextrin) to enhance the stability, by forming an inclusion complex.
Creaming stability might be a way to assess the thermodynamic stability of emulsion prepared. Not to forget the concentration of lecithin, pH, other gums (gellan, gum Arabic) etc are all factors to be considered when expanding this research. In many cases, lecithin is used along with milk or other major constituents, where the interactions of proteins with lecithin help to stabilize the preparation.In the food industry, emulsifiers are usually used with other thickeners, such as xanthan gum, to give better emulsion stability.
A good reference to check on emulsion would be chapter 6 from Food Emulsifiers & their applications book by Hasenhuettl et al.