Up-to-date knowledge on the "potato taste" of the arabica coffee coming from african great lakes region

The potato taste of the coffee coming from the African Great Lakes region, although of low occurrence, represents a serious risk for the coffee sector of this region. Indeed, the coffee from this region is among the best in the world and it is important to avoid this off-flavor from the produced coffee. This off-flavor is due to the presence of the molecule: isopropyl-2-methoxyl-3-pyrazine, produced following the introduction of a bacterium of the family of Enterobacteriaceae into the cherries. The taxonomy of this unknown bacterium is presented in several phylogenetic trees. On a RNA 16S phylogenetic tree, this bacterium is close to Escherichia coli; on a rpoB phylogenetic tree it is near Enterobacter agglomerans and Erwinia psidii. The introduction of this bacterium is facilitated by the stings of the insect Antestiopsis orbitalis. Indeed, it was shown that the protection of the coffee plantations against this insect decreased the occurrence of the "Potato Taste"; on the other hand it was never shown that this insect was a vector of the involved bacterium. This assumption of vector role will have to be tested. The insect causes other damages and its aggregate distribution makes difficult the estimation of the population levels. More work has to be done to remove this threat from the coffee of the African Great Lakes region. Hand sorting of coffee beans is effective in reducing the incidence of the potato taste and there are now modern color sorting machines highly sensitive at different coffee export companies, which detect defective beans before further cupping tests. Nevertheless, the identification of the bacterium with the new tools of molecular biology is essential and will allow a better understanding of the ecology of this bacterium in the African Great Lakes region landscape. (Résumé d'auteur