ABSTRACT
The flavour of a cup of coffee is the final expression and perceptible result of a long chain of chemical transformations from the seed to the cup. The green bean has only a faint smell but contains all the precursors required to generate coffee aroma during roasting. The aroma of coffee is intrinsically related to the chemical composition of the seeds, which during roasting undergo innumerable chemical modifications, generating a wide variety of volatile compounds. More than 900 volatile compounds were identified to date in roasted coffee beans (Flament, 2002). One of the main aims of research on coffee quality is (i) to establish relationships between the chemical composition of green beans and beverage quality, that is, to identify the key precursors involved in the development of aroma and flavour (and conversely in off-flavours and defects) and (ii) to characterize the main factors that influence their accumulation during bean development. Aroma precursors are synthesized and/or transported in the endosperm (the tissue that constitutes most
of the coffee seed volume) during seed development and maturation. Understanding coffee quality requires the identification of all developmental processes that govern the accumulation of these compounds, that is, biosynthetic genes and enzymes and transcriptional (and post-transcriptional) regulatory processes. Progress in these areas will ultimately help in developing robust genomics/metabolomics fingerprints of coffee bean origin and quality, and in assisting breeding programmes dedicated to coffee quality by providing novel targets and strategies. Indeed, the creation of new varieties, the optimization of agricultural practices and post-harvest technologies, all requires prior knowledge about factors that determine coffee cup quality. The chemical composition of the seeds is directly affected by a wide range of parameters, including coffee species and cultivars, climate, soil, agricultural practices, post-harvest processing, green bean storage, roasting and roasted bean storage. Among them, this chapter aims at summarizing our current knowledge on biosynthetic pathways for key aroma precursors and genetic and environmental factors that influence their accumulation during seed development.
