Valorization of spent coffee grounds by supramolecular solvent extraction

Abstract

In this study, we assess the potential of supramolecular solvents (SUPRAS) for valorization of spent coffee grounds (SCG). SUPRAS, made up of self-assembled amphiphilic aggregates dispersed in an aqueous or hydro-organic medium, are excellent extractants that provide multiple binding interactions (hydrogen bonds, dispersion, dipole-dipole, etc.) and microenvironments of different polarity due to their special internal architecture. In this work, SUPRAS made up of different amphiphiles (decanoic acid and hexanol) and hydro-organic media (water-ethanol and water-tetrahydrofuran) were investigated for extraction of bioactives from SCG. Extraction was optimized from the yield obtained for caffeine and 5-chlorogenic acid, that were considered as model compounds. Under optimal extraction conditions, the profile of bioactive compounds in the extracts was screened by liquid chromatography tandem mass spectrometry and the total phenolic content was estimated. The antioxidants and antimicrobial properties of the extracts were also evaluated. Bioactive compounds were extracted from wet SCG up to 3.32 mg/g and 4.3 mg/g SCG of caffeine and chlorogenic acid, respectively. Extracts showed antioxidant capacity by different assays (DPPH, TEAC, FRAP) in accordance with their high total phenolic content (60.1 mg CGA per mg of extracted dry SCG). SUPRAS offered advantages in terms of rapidity (extraction for 1 min) and simplicity (the process involved stirring and centrifugation at room temperature), thus avoiding costly processes based on high pressure and temperature. Furthermore, SUPRAS extracts exhibited certain degree of antimicrobial effects against, S. aureus and B. cereus and a high effect against S. enterica and P. putida.