Bitterness values for traditional tonic plants of southern Africa.

ETHNOPHARMACOLOGICAL RELEVANCE: Bitterness values have been determined for southern African plant species that are traditionally used as tonics (imbizas or 'musa-pelo) to alleviate the symptoms of stress and a variety of ailments related to the digestive system.

AIM OF THE STUDY: To measure and present, for the first time, the bitterness values of 15 of the best-known and most widely used tonic plants in southern Africa in order to find a rationale for their traditional use in improving appetite and treating digestive ailments.

RESULTS: Most of the plants were found to be very bitter, with bitterness values comparable to those reported for internationally well-known bitter tonics such as Artemisia absynthium L. and Gentiana lutea L.

CONCLUSIONS: The relatively high bitterness values obtained for all of the plants indicate that their alleged value in improving digestion and appetite may at least be partly ascribed to the bitter tonic (amarum) effect, i.e., the stimulation of gastric juices via the nervus vagus. It may be interesting to examine the chemical compounds responsible for the bitter taste, as well as the possible links between bitterness and the anecdotal anti-stress properties ascribed to these species.