Antioxidant activities and major antioxidants were investigated in the methanolic extracts of roasted and spent coffee to evaluate the feasibility of spent coffee as a source of functional ingredients. Phenolic compounds, such as gallic acid, protocatechuic acid, and chlorogenic acid, and nitrogenous compounds, including trigonelline and caffeine, were identified. Caffeine was the most abundant compound, followed by chlorogenic acid. Despite the significant reduction of antioxidants, 2,2,-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was retained in more than 95% of roasted coffee. The retentions of superoxide dismutase (SOD)-like activity and ferric reducing antioxidant power (FRAP) were 65-90 and 46-60%, respectively. Gallic acid had a positive correlation with SOD-like activity, whereas protocatechuic acid positively correlated with FRAP, suggesting that the major compounds contributing to each antioxidant activity are different. These results show that spent coffee can be used as an antioxidant source for functional foods and cosmetic products to improve antioxidant properties.
Keywords: Caffeine; Chlorogenic acid; DPPH; FRAP; SOD-like; Spent coffee.