Biochemical and molecular characterization of enzyme controlling sugar metabolism during coffee bean development [S19-14]

In green coffee beans, the carbohydrate fraction represents about half of the dry weight, and participates in the extensive chemical changes associated during coffee roasting. Among these carbohydrates, sucrose is considered as the major precursor of coffee flavour and aroma, because it is rapidly degraded during the roasting or by steam treatment. Sucrose breakdown during roasting leads to anhydro-sugars (like 1,6 anhydro-glucose, arabinose, glyoxal), which then react in a number of ways leading to a wide range of compounds (i.e. aliphatic acids, hydroxymethyl furfural and other furans, pyrazine and carbony compounds). Despite these important effects, little is known about sugar metabolism (gene and protein expression/regulation) in coffee, particularly during the long phase of the bean development. Therefore, the aim of the present work was to increase our basic knowledge about sugar metabolism in coffee, mainly to understand the sink-source relationships during the development of coffee bean and their effects on the coffee bean size. To achieve these goals, cDNA sequences of invertase (EC 3.2.1.26), sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) were cloned in our laboratories or identified from the Coffee Genome Project database (http://arara.lbi.ic.unicamp.br/cafe/). The use of this sequences to investigate their expression throughout coffee bean development via northern analysis and RT-PCR experiments is presented. At the biochemical level, kinetic characteristics and preliminary results of invertase and sucrose synthase enzymatic activities detected during the coffee bean development will be also presented and discussed in relation to evolution of tissues and sugar content. In addition, branches bearing fruits were fed with 14CO2 and the radioactivity distribution determined in the different tissues of the fruits. (Texte intégral)