Résumé
Caffeine is the most popular purine alkaloid, found mainly in teas, guarana, yerba mate, guayusa, cocoas, and coffees. Caffeine content ranges from 0% to >3% and 0% to <1% dmb in African and Indian Ocean Island (IOI) coffee beans, respectively. In Africa, species from the East coast have low to medium caffeine content in their beans, while those from the West and Center have medium to high levels. Despite exceptions in Africa and Madagascar, global trends in caffeine content show a progressive increase from East to West along the geographic distribution of the genus. For African species, the longer the flowering-fructification period, the higher the caffeine content. Yet, caffeine absence is not due to a short flowering-fructification period. IOI species show no correlation: all species of long flowering-fructification periods are caffeine-poor or caffeine-free, while the two medium/rich species have short flowering-fructification periods. Genetics tells us that the recessive allele of one gene controls the absence of caffeine, while the overall caffeine content is under polygenic control with strong genetic effects. Recently, the genomics taught us that the absence of at least one gene involved in the metabolic pathway of caffeine is necessary for the cases of the naturally caffeine free species from Madagascar.