Changes to the content of sugars, sugar alcohols, myo-inositol, carboxylic acids and inorganic anions in developing grains from different varieties of Robusta ( Coffea canephora) and Arabica ( C. arabica) coffees

Abstract

Changes in concentration of mono- and oligosaccharides, sugar alcohols, myo-inositol, carboxylic acids and inorganic anions in coffee grains were analysed during grain development in three cultivars of Coffea arabica L (Arabica) and two of C. canephora L var. Robusta (Robusta) by high performance anion exchange chromatography coupled to pulsed electrochemical detection (HPAE-PED). The majority of the components analysed either decreased in concentration during the first half of the development period or accumulated steadily during the latter half of the period. The profiles are taken to indicate relationships between the perisperm, the principal tissue in the young grain and the endosperm during maturation. While most of the free sugar in the mature grain is accounted for by sucrose, fructose and glucose are both at higher concentrations in the perisperm. Considerable amounts of myo-inositol (3–4% dry weight (DW)) are found in young grains, while only the phosphorylated form phytic acid occurs in mature grains (0.3–0.6% DW). Quinic acid, which is present in very low amounts in mature endosperm, represents between 6 and 16% DW in young grains, this possibly being the major precursor pool for the high amounts of chlorogenic acids (5–10% DW) which are a characteristic of mature coffee grains. Of the other organic acids analysed, citric and malic acids are dominant in the mature grain, with higher concentrations in Arabica than Robusta. The results are discussed with respect to the potential implications for transport mechanisms in developing coffee grains and also the importance of the compounds analysed for industrial quality and flavour.