Orange and Pineapple Juice are both highly acidic. Make sure the broth you use is not high in acids, i.e. made mainly of carrots, parsnips, broccoli, etc. but NO tomato
That's probably the best way to go.
It might very well be that the cayenne caused the heartburn, as lemon juice does not cause heart burn, it relieves it. (It's actually alkaline) So it might help just mixing some room temperature water with a little bit of lemon juice (no cayenne, no maple syrup).