Characterization of high molecular weight coffee fractions and their fermentation by human intestinal microbiota

To investigate the structure and fermentability of high M(r) components of coffee brews by human gut bacteria Arabica coffee samples of three different degrees of roast (light, medium, and dark) were used for drip brew preparations and fractionation by ultrafiltration with different M(r) cut-offs. Total carbohydrates of the fractions ranged from 28.6 g/100 g to 56.7 g/100 g. Galactomannans and arabinogalactans were the main polysaccharides and made up between one-fourth and one-half of the respective coffee fraction. After 24 h of incubation with a human fecal suspension the polysaccharides of all fractions were extensively degraded. A decrease in the absorbance values at 405 and 280 nm, respectively, indicated that also chemically noncharacterized UV-active components such as Maillard reaction products, had been partially degraded or modified by the human gut bacteria. The remainder after 24 h of fermentation still showed antioxidant activity. Bacterial cells belonging to the Bacteroides-Prevotella group increased 2- to 40-fold during fermentation depending on the M(r) range of the fraction and the degree of roast. The production of high amounts of acetate and propionate is in accordance with a role of these bacteria in the degradation of high M(r) components from coffee.