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- Influence of co-solvents on the supercritical extraction kinetics of spent coffee grounds: experimental and modelling studiesPublication . Coelho, Jose; Filipe, Rui; Robalo, Maria Paula; Boyadzieva, Stanislava S.; Cholakov, Georgi; Stateva, Roumiana P.Coffee is one of the most widely used beverages. An estimated 3.5 billion cups of coffee are drunk worldwide every day. In EU alone, for the period 2011-2013, 2.5 Mt of coffee were consumed. Taking into consideration that the production of coffee in 2015 was approximately 9 Mt and that from each kg of coffee 0.91 kg of solid waste is produced, the importance of a further valorization of this residue becomes obvious. In recent years, the biorefinery concept has been identified as the most promising route for employment of the full potential of a biomass by maximizing its conversion into high value products. Its main bottleneck, however, is how to extract the energy and non- energy compounds from the biomass without damaging one or more of the components, e.g. those which are heat sensitive. Spent coffee grounds (SCGs) contain large amounts of fatty acids, lignin, cellulose, hemicellulose, etc. and can be exploited as an excellent source of value-added energy and non-energy related products (e.g, antioxidants and other functional additives).
- Supercritical CO2 extraction of spent coffee grounds. Influence of co-solvents and characterization of the extractsPublication . Coelho, Jose; Filipe, Rui; Robalo, M. Paula; Boyadzhieva, Stanislava; Cholakov, Georgi; Stateva, RoumianaSpent coffee grounds (SCGs) were extracted with supercritical CO2 at temperatures of 313 K and 333 K, pressures up to 50.0 MPa and different scCO(2) flow rates. The addition of co-solvents isopropanol, ethanol and ethyl lactate decreased the time to achieve the maximum oil yield, to half of that with pure CO2. Analysis of the extracted oils by NMR, showed that caffeine content was (0.56-3.96) % and DUFA and MUFA contents changed within (39.8-42.0) % and (12.9-15.8) %, respectively. The analyses of fatty acids performed by GC-FID revealed the composition of the oils being 76 % of the total constituted by palmitic and linoleic esters. The DPPH antioxidant capacity was improved up to 12.5 times with co-solvents. The kinetics of oil extraction from SCGs with pure scCO(2) was modeled successfully by combining for the first time representation of the oil mixture by a single virtual molecule with group contribution methods.