Antioxidant and prooxidant activity of spent coffee extracts by isothermal calorimetry

Abstract

This work aims to determine the antioxidant and prooxidant activity of spent coffee extracts obtained with (1) a low-pressure (LP) extraction with ethanol and (2) a subcritical fluid (SF) extraction with carbon dioxide and ethanol as co-solvent. The antioxidant capacity of both extracts was measured by two calorimetry-based approaches. The first assessed the capacity of the extracts to inhibit the lipid oxidation of a standard solution of linseed oil. The second measured the capacity of the extracts to inhibit the radical decomposition of AIBN, a free radical generator. Both approaches showed that LP extracts had a higher antioxidant capacity than SF extracts. However, when SF extracts were further purified with ethanol, the resulting sub-fraction showed an antioxidant capacity comparable to that of LP extracts. Conversely, when SF extracts were purified with hexane, the resulting sub-fraction exhibited a prooxidative capacity, either speeding-up the oxidation of linseed oil and the decomposition rate of AIBN. Such prooxidative capacity was explained with the high content of unsaturated fatty acids contained in the hexane sub-fraction. Overall, this work showed that LP technique provided an extract with high antioxidant activity. Moreover, the results indicated that SF extraction could also serve as a technique for the recovery of antioxidants from spent coffee once the extract was furthermore purified and the lipid fraction removed.