COMPOSITION OF GREEN COFFEE FRACTIONS AND THEIR CONTRIBUTION TO THE VOLATILE PROFILE FORMED DURING ROASTING

A sequential fractionation method to isolate water-soluble fractions o f green Arabica coffee is described. Low- and high-molecular-weight fr actions were obtained by treating the dried water extract with aqueous ethanol (80%, v/v). High-performance gel filtration chromatography wa s used to show some differences in molecular weight distribution betwe en fractions. Flavour precursors were detected in both fractions. Arab inogalactan was the main polysaccharide found in the water-soluble hig h-molecular-weight fraction, together with large amounts of protein. I mportant flavour precursors such as sucrose, trigonelline and chloroge nic acid were detected in the low-molecular-weight fraction. A simple and rapid headspace method was developed to obtain the volatile profil es produced by the roasted fractions. Volatiles were immediately colle cted after roasting in a sealed tube and submitted to gas chromatograp hy. The chromatographic profiles obtained showed considerable differen ces between fractions and revealed an important contribution to aroma formation.