Decaffeination of guarana seeds in a microextraction column using water-saturated CO_2

摘要

Experimental data on the reduction of the caffeine content of guarana seeds with water-saturated supercritical carbon dioxide were obtained in order to provide information on the ability of supercritical fluids for the decaffeination of widely consumed caffeine-rich natural products. The extraction was performed using a semi-continuous flow high-pressure micro-extraction apparatus at 40 and 70 deg C and pressures of 100,200 and 400 bar. Carbon dioxide flow rates of 5.7 and 9.4 g min~(-1) were used. The extraction curves obtained showed the existence of thermodynamic solubility dependent, intermediate and diffusion controlled regions. Extraction at 400 bar and 70 deg C using water-saturated supercritical carbon dioxide at a flow rate of 5.7 g min~(-1) allowed the removal of almost 98% of the initial caffeine content in wet ground guarana seeds, in a period of 240 min. When extractoins were performed at lower pressures or temperatures, additional time and larger amounts of carbon dioxide were necessary to achieve the same yield. Increasing carbon dioxide fow rate did not present any economic advantage unless the extraction was limited to the thermodynamic solubility region. For total extraction of caffeine, the use of low flow rates resulted in a similar final product yield but at a much lower solvent consumption. A retrograde behavior for the extraction of caffeine from guarana seeds was also observed at 100 bar for the 40 and 70 deg C isotherms.