Concentration of Coffee Employing CO2 Gas Hydrates: Exploring Concentration Limits and Aroma Profiles
摘要
CO2 gas hydrate formation was triggered in degassed coffee solutions at 7.5 wt.% in a stirred tank reactor for concentration applications at target conditions of 1 °C and 4.1 MPa. The total solids content (TS) of the hydrate and the concentrate phase was compared to results when triggering gas hydrate formation in 7.5 wt.% sugar solutions (galactose, arabinose, mannose) or non-degassed coffee solutions using the same process parameters. Neither the degassing step nor the change of sample (coffee/sugar) had an influence on the final TS of the concentrate (12–14 wt.%). This emphasizes that the proposed process can be used for concentration regardless of the exact sample composition. However, solid losses in the hydrate phase were higher in the sugar (5 wt.%) than in the coffee solutions (2 wt.%). Additionally, the first ever aroma analysis of coffee concentrated using gas hydrates was conducted by gas chromatography coupled with mass spectrometry. Thirty key coffee aroma compounds were identified in both concentrate and hydrate phase and were found to be unselectively distributed. Furthermore, aroma profiles did not differ substantially from the liquid prior to concentration. This confirms that gas hydrate technology can be used as a gentle way of concentrating liquids, even for fragile compounds. Additionally, gas hydrate formation was triggered in 13 and 21 wt.% coffee solutions to test options for a stepwise concentration technology. The TS of the hydrate and the concentrate phase increased proportionally to the initial TS, reaching a final concentration of 40 wt.%.