CONICET | Buscador de Institutos y Recursos Humanos

In this work, we studied the decaffeination of yerba mate using a ncCO2 Soxhlet extractionmethod at 283 K and 4.5 MPa. Chopped yerba mate leaves are processed in a dried form orimpregnated with hydrated ethanol as a cosolvent. A maximum overall extraction yieldof 2.68 wt. % is achieved when the water content in the cosolvent mixture is set at 15.0 wt. %. Thisresulted in a 32.8 wt. % reduction in the caffeine content of yerba mate leaves impregnatedwith a cosolvent-to-feed ratio of 1.0 g g-1. Interestingly, regardless of the percentage of waterin the cosolvent mixture, less than 1.6 % of the total content of two of the main antioxidantcompounds present in yerba mate leaves, caffeic acid and chlorogenic acid, arecoextracted in the process. The overall extraction yield remains close to the maximum whencosolvents with a water percentage between 4.4 and 22.5 wt. % are used. In contrast, overall extraction yields below 1.0 wt. % are obtained when cosolvents with water percentages exceeding 30 wt. % are used. In order to explain this observation, the thermodynamic phase equilibrium at 283 K and 4.5 MPa for a ternary CO2-ethanol-water mixture is modeled using the group contribution plusassociation equation of state (GCA-EoS). The predictions of the model reveal that when the water percentage in the cosolvent is near that of maximal extraction yield, the CO2-ethanolwatermixture forms a single liquid phase even at high CO2 contents, which is expected to favor the extraction process. Under low extraction yield conditions, where the water percentage exceeds 30 wt. %, the GCA-EoS predicts a phase split into a water-rich and a CO2-rich liquid phase at low CO2contents. In this context, it is expected for the CO2-rich liquid phase to exhibit a rather low solvent power, and for the water-rich phase to act as a diffusion barrier, thus hindering the extraction.

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