Composition of green coffee fractions and their contribution to the volatile profile formed during roasting

A sequential fractionation method to isolate water-soluble fractions of green Arabica coffee is described. Low- and high-molecular-weight fractions were obtained by treating the dried water extract with aqueous ethanol (80%, v/v). High-performance gel filtration chromatography was used to show some differences in molecular weight distribution between fractions. Flavour precursors were detected in both fractions. Arabinogalactan was the main polysaccharide found in the water-soluble high-molecular-weight fraction, together with large amounts of protein. Important flavour precursors such as sucrose, trigonelline and chlorogenic acid were detected in the low-molecular-weight fraction. A simple and rapid headspace method was developed to obtain the volatile profiles produced by the roasted fractions. Volatiles were immediately collected after roasting in a sealed tube and submitted to gas chromatography. The chromatographic profiles obtained showed considerable differences between fractions and revealed an important contribution to aroma formation.