Coffee pulp contains natural antioxidants like hydroxycinnamic acids, most of which
are covalently linked to the cell wall. These compounds can be released by fermentation or
enzymatic processes. In this study, the antioxidant properties of fermented and nonfermented
coffee pulp have been evaluated. Coffee pulp was fermented by solid-state fermentation
using the fungus Aspergillus tamarii. Fermented and nonfermented samples of
coffee pulp were extracted with aqueous methanol followed by alkaline hydrolysis. In
both cases, the total polyphenol concentration was quantified by Folin-Ciocalteu method,
then hydroxycinnamic acids were concentrated using ethyl acetate and quantified by HPLC.
The antioxidant properties of samples were determined by radical monocation of 2,2’-azinobis-(
3-ethylbenzothiazoline-6-sulphonic acid) [ABTS]·+: the antioxidant activity was determined
by kinetic parameters known as ED50, tED50 and antiradical efficiency (AE). Fermented
extracts containing free hydroxycinnamic acids showed better antiradical activity
against [ABTS]·+ than the other nonfermented ones. There were no significant differences
in the total content of polyphenols in fermented and nonfermented coffee pulp, but the
content of total hydroxycinnamic acids was higher in the nonfermented coffee pulp extracts
(47.1 g/kg) than in the fermented coffee pulp (30.9 g/kg). Nevertheless, the fermentation
process increased the fraction of free hydroxycinnamic acids (47 %) and consequently
decreased those covalently linked to the cell wall. The results of the antioxidant
activity assays could be explained by the presence of free hydroxycinnamic acids. Fermented
coffee pulp assays showed that free hydroxycinnamic acids were metabolised by A. tamarii.
This study shows the potential of using coffee pulp as a natural source of antioxidants.