What could be the basic ingredients that potentiate sourness and bitterness?
About any acid will deliver a sour taste from H+, along with whatever taste the corresponding anion brings along.
Most alkaloids are bitter.The term covers a wide range of different chemicals, mostly including nitrogen qnd oxygen as part of their structure. There are likely quite a few bitter compounds which are not alkaloids, but none spring to mind at the moment. Bitter is a far more complex response than sour or sweet.