Rheology modifier

Guar gum is primarily a thickener while xanthan is
both a thickener and stabilizer...The latter is more functional and more effective as rheology modifier in many applications..

I was told xanthan gum tends to foam more. Is that correct?

Xanthan gum.stabilizes emulsion. So it can stabilize foam that is indirectly created from.beveeage components like some traces of protein..
In juices the amount of xantham gum used is little 0.1% so its unlikely the cause of foam formation.
In other liquid concoction having up to 0.5% xanthan gum.,the produced high viscosity can induce foam.formation as the viscous liquid can entrap air if agitated intensively. .

Both works in acid pH.
Precipitations cause: concentrations, interaction with others ingredients.