Spent Coffee Grounds as a Renewable Source of Bioactive Compounds

Spent coffee grounds (SCG) are the main residues from the soluble coffee industry. The objective of this work was to evaluate different extraction methods of oil and diterpenes (kahweol and cafestol) from SCG, such as solid–liquid extraction, supercritical extraction or direct saponification, as well as to determine the phenolic composition and antioxidant capacities (by radical scavenging activity, inhibition of linoleic acid oxidation and β-carotene bleaching method) of SCG and defatted SCG. Among assayed oil extraction methods, the Soxhlet extraction process recovered the highest oil amounts (26.4%). The free fatty acid profile showed a high content of polyunsaturated fatty acids (50%) for the lipid fraction extracted from SCG by each method used, mainly linoleic and palmitic acids (about 45 and 30%, respectively). SCG was found to be an important source of polyphenolic compounds, showing 255 and 273 mg GAE/g dm in ethanolic extracts from SCG and defatted SCG, respectively, and was active as an antioxidant. The method that reached the highest level of diterpenes (214 mg/100 g SCG for kahweol and 466 mg/100 g SCG for cafestol) was direct saponification compared with the saponification of oil extracted by solid–liquid extraction or supercritical extraction. Finally, the presence of bioactive compounds of SCG identified in this study could be of great interest for the food, cosmetic and pharmaceutical industries, giving added value to a residue generated from instant coffee industrial processing, readily available in large quantities.