Manufacturers will give a hydration temperature for their gums that may differ from the generic temperatures you'll read elsewhere. Gum molecules are heterogenous; from any source there will be different versions of the molecules that will hydrate at different temperatures. The gum companies make their formulas by carefully selecting the source and refining for a particular range of molecules for each product.
But the hydration temperature they give is still most likely a recommendation. The locust bean gum I use is supposed to hydrate at 80°C. When I asked the manufacturer what would happen if I only cook it to 75°C°, the rep said that probably 90% of it would hydrate. Which is easy (and maybe even unnecessary) to compensate for. But probably at 50°C it would be completely inneffective.
